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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Stellar evolution</span></span>

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<p><b>Stellar evolution</b> is the process by which a <a href="Star" title="Star">star</a> changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current <a href="Age_of_the_universe" title="Age of the universe">age of the universe</a>. The table shows the lifetimes of stars as a function of their masses.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> All stars are formed from <a href="Gravitational_collapse" title="Gravitational collapse">collapsing</a> clouds of gas and dust, often called <a href="Nebula" title="Nebula">nebulae</a> or <a href="Molecular_cloud" title="Molecular cloud">molecular clouds</a>. Over the course of millions of years, these <a href="Protostar" title="Protostar">protostars</a> settle down into a state of equilibrium, becoming what is known as a <a href="Main_sequence" title="Main sequence">main sequence</a> star.

</p><p><a href="Nuclear_fusion" title="Nuclear fusion">Nuclear fusion</a> powers a star for most of its existence. Initially the energy is generated by the fusion of <a href="Hydrogen_atoms" class="mw-redirect" title="Hydrogen atoms">hydrogen atoms</a> at the <a href="Stellar_core" title="Stellar core">core</a> of the main-sequence star. Later, as the preponderance of atoms at the core becomes <a href="Helium" title="Helium">helium</a>, stars like the <a href="Sun" title="Sun">Sun</a> begin to fuse hydrogen along a spherical shell surrounding the core. This process causes the star to gradually grow in size, passing through the <a href="Subgiant" title="Subgiant">subgiant</a> stage until it reaches the <a href="Red_giant" title="Red giant">red-giant</a> phase. Stars with at least half the mass of the Sun can also begin to generate energy through the fusion of helium at their core, whereas more-massive stars can fuse heavier elements along a series of concentric shells. Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense <a href="White_dwarf" title="White dwarf">white dwarf</a> and the outer layers are expelled as a <a href="Planetary_nebula" title="Planetary nebula">planetary nebula</a>. Stars with around ten or more times the mass of the Sun can explode in a <a href="Supernova" title="Supernova">supernova</a> as their inert iron cores collapse into an extremely dense <a href="Neutron_star" title="Neutron star">neutron star</a> or <a href="Black_hole" title="Black hole">black hole</a>. Although the <a href="Universe" title="Universe">universe</a> is not old enough for any of the smallest <a href="Red_dwarf" title="Red dwarf">red dwarfs</a> to have reached the end of their existence, <a href="Stellar_model" class="mw-redirect" title="Stellar model">stellar models</a> suggest they will slowly become brighter and hotter before running out of hydrogen fuel and becoming low-mass white dwarfs.<sup id="cite_ref-endms_2-0" class="reference"><a href="#cite_note-endms-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime, and by simulating <a href="Stellar_structure" title="Stellar structure">stellar structure</a> using <a href="Computer_model" class="mw-redirect" title="Computer model">computer models</a>.

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<div class="mw-heading mw-heading2"><h2 id="Star_formation">Star formation</h2></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Star_formation" title="Star formation">Star formation</a></div>

<div class="mw-heading mw-heading3"><h3 id="Protostar">Protostar</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Protostar" title="Protostar">Protostar</a></div>

<p>Stellar evolution starts with the <a href="Gravitational_collapse" title="Gravitational collapse">gravitational collapse</a> of a <a href="Giant_molecular_cloud" class="mw-redirect" title="Giant molecular cloud">giant molecular cloud</a>. Typical giant molecular clouds are roughly 100 light-years (9.5<span style="margin:0 .15em 0 .25em">×</span>10<sup>14</sup> km) across and contain up to 6,000,000 <a href="Solar_mass" title="Solar mass">solar masses</a> (1.2<span style="margin:0 .15em 0 .25em">×</span>10<sup>37</sup> <a href="Kilogram" title="Kilogram">kg</a>). As it collapses, a giant molecular cloud breaks into smaller and smaller pieces. In each of these fragments, the collapsing gas releases <a href="Gravitational_potential" title="Gravitational potential">gravitational potential energy</a> as heat. As its temperature and pressure increase, a fragment condenses into a rotating ball of superhot gas known as a <a href="Protostar" title="Protostar">protostar</a>.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Filamentary structures are truly ubiquitous in the molecular cloud. Dense molecular filaments will fragment into gravitationally bound cores, which are the precursors of stars. Continuous accretion of gas, geometrical bending, and magnetic fields may control the detailed fragmentation manner of the filaments. In supercritical filaments, observations have revealed quasi-periodic chains of dense cores with spacing comparable to the filament inner width, and embedded two protostars with gas outflows.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

</p><p>A protostar continues to grow by <a href="Accretion_(astrophysics)" title="Accretion (astrophysics)">accretion</a> of gas and dust from the molecular cloud, becoming a <a href="Pre-main-sequence_star" title="Pre-main-sequence star">pre-main-sequence star</a> as it reaches its final mass. Further development is determined by its mass. Mass is typically compared to the mass of the <a href="Sun" title="Sun">Sun</a>: 1.0 <i>M</i><sub>☉</sub> (2.0<span style="margin:0 .15em 0 .25em">×</span>10<sup>30</sup> kg) means 1 solar mass.

</p><p><a href="Protostar" title="Protostar">Protostars</a> are encompassed in dust, and are thus more readily visible at <a href="Infrared" title="Infrared">infrared</a> wavelengths.

Observations from the <a href="Wide-field_Infrared_Survey_Explorer" title="Wide-field Infrared Survey Explorer">Wide-field Infrared Survey Explorer</a> (WISE) have been especially important for unveiling numerous galactic <a href="Protostar" title="Protostar">protostars</a> and their parent <a href="Star_cluster" title="Star cluster">star clusters</a>.<sup id="cite_ref-wright_5-0" class="reference"><a href="#cite_note-wright-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-ma2013_6-0" class="reference"><a href="#cite_note-ma2013-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Brown_dwarfs_and_sub-stellar_objects">Brown dwarfs and sub-stellar objects</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Brown_dwarf" title="Brown dwarf">Brown dwarf</a></div>

<p>Protostars with masses less than roughly 0.08 <i>M</i><sub>☉</sub> (1.6<span style="margin:0 .15em 0 .25em">×</span>10<sup>29</sup> kg) never reach temperatures high enough for <a href="Nuclear_fusion" title="Nuclear fusion">nuclear fusion</a> of hydrogen to begin. These are known as <a href="Brown_dwarf" title="Brown dwarf">brown dwarfs</a>. The <a href="International_Astronomical_Union" title="International Astronomical Union">International Astronomical Union</a> defines brown dwarfs as stars massive enough to <a href="Deuterium_burning" class="mw-redirect" title="Deuterium burning">fuse deuterium</a> at some point in their lives (13 <a href="Jupiter_mass" title="Jupiter mass">Jupiter masses</a> (<a href="Jupiter_mass" title="Jupiter mass"><var>M</var><sub>J</sub></a>), 2.5 × 10<sup>28</sup> kg, or 0.0125 <var>M</var><sub>☉</sub>). Objects smaller than <span class="nowrap">13</span> <var>M</var><sub>J</sub> are classified as <a href="Sub-brown_dwarf" title="Sub-brown dwarf">sub-brown dwarfs</a> (but if they orbit around another stellar object they are classified as planets).<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> Both types, deuterium-burning and not, shine dimly and fade away slowly, cooling gradually over hundreds of millions of years.

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<div class="mw-heading mw-heading3"><h3 id="Main_sequence_stellar_mass_objects">Main sequence stellar mass objects</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Main_sequence" title="Main sequence">Main sequence</a></div>

</div>

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<div class="thumbcaption">The evolutionary tracks of <a href="Stars" class="mw-redirect" title="Stars">stars</a> with different initial masses on the <a href="Hertzsprung%E2%80%93Russell_diagram" title="Hertzsprung–Russell diagram">Hertzsprung–Russell diagram</a>. The tracks start once the star has evolved to the <a href="Main_sequence" title="Main sequence">main sequence</a> and stop when <a href="Nuclear_fusion" title="Nuclear fusion">fusion</a> stops (for massive stars) and at the end of the <a href="Red-giant_branch" title="Red-giant branch">red-giant branch</a> (for stars 1 <var>M</var><sub>☉</sub> and less).<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><br>A yellow track is shown for the <a href="Sun" title="Sun">Sun</a>, which will become a <a href="Red_giant" title="Red giant">red giant</a> after its main-sequence phase ends before expanding further along the <a href="Asymptotic_giant_branch" title="Asymptotic giant branch">asymptotic giant branch</a>, which will be the last phase in which the Sun undergoes fusion.</div>

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<p>For a more-massive protostar, the core temperature will eventually reach 10 million <a href="Kelvin" title="Kelvin">kelvin</a>, initiating the <a href="Proton%E2%80%93proton_chain_reaction" class="mw-redirect" title="Proton–proton chain reaction">proton–proton chain reaction</a> and allowing <a href="Hydrogen" title="Hydrogen">hydrogen</a> to fuse, first to <a href="Deuterium" title="Deuterium">deuterium</a> and then to <a href="Helium" title="Helium">helium</a>. In stars of slightly over 1 <i>M</i><sub>☉</sub> (2.0<span style="margin:0 .15em 0 .25em">×</span>10<sup>30</sup> kg), the carbon–nitrogen–oxygen fusion reaction (<a href="CNO_cycle" title="CNO cycle">CNO cycle</a>) contributes a large portion of the energy generation. The onset of nuclear fusion leads relatively quickly to a <a href="Hydrostatic_equilibrium" title="Hydrostatic equilibrium">hydrostatic equilibrium</a> in which energy released by the core maintains a high gas pressure, balancing the weight of the star's matter and preventing further gravitational collapse. The star thus evolves rapidly to a stable state, beginning the <a href="Main_sequence" title="Main sequence">main-sequence</a> phase of its evolution.

</p><p>A new star will sit at a specific point on the main sequence of the <a href="Hertzsprung%E2%80%93Russell_diagram" title="Hertzsprung–Russell diagram">Hertzsprung–Russell diagram</a>, with the main-sequence <a href="Spectral_type" class="mw-redirect" title="Spectral type">spectral type</a> depending upon the mass of the star. Small, relatively cold, low-mass <a href="Red_dwarf" title="Red dwarf">red dwarfs</a> fuse hydrogen slowly and will remain on the main sequence for hundreds of billions of years or longer, whereas massive, hot <a href="O-type_main-sequence_star" title="O-type main-sequence star">O-type stars</a> will leave the main sequence after just a few million years. A mid-sized <a href="G-type_main-sequence_star" title="G-type main-sequence star">yellow dwarf</a> star, like the Sun, will remain on the main sequence for about 10 billion years. The Sun is thought to be in the middle of its main sequence lifespan.

</p>

<div class="mw-heading mw-heading3"><h3 id="Planetary_system">Planetary system</h3></div>

<p>A star may gain a <a href="Protoplanetary_disk" title="Protoplanetary disk">protoplanetary disk</a>, which furthermore can develop into a <a href="Planetary_system" title="Planetary system">planetary system</a>.

</p>

<div class="mw-heading mw-heading2"><h2 id="Mature_stars">Mature stars</h2></div>

<p>Eventually the star's core exhausts its supply of hydrogen and the star begins to evolve off the <a href="Main_sequence" title="Main sequence">main sequence</a>. Without the outward <a href="Radiation_pressure" title="Radiation pressure">radiation pressure</a> generated by the fusion of hydrogen to counteract the force of <a href="Gravity" title="Gravity">gravity</a>, the core contracts until either <a href="Electron_degeneracy_pressure" title="Electron degeneracy pressure">electron degeneracy pressure</a> becomes sufficient to oppose gravity or the core becomes hot enough (around 100 MK) for <a href="Helium_fusion" class="mw-redirect" title="Helium fusion">helium fusion</a> to begin. Which of these happens first depends upon the star's mass.

</p>

<div class="mw-heading mw-heading3"><h3 id="Low-mass_stars">Low-mass stars</h3></div>

<p>What happens after a low-mass star ceases to produce energy through fusion has not been directly observed; the <a href="Universe" title="Universe">universe</a> is around 13.8 billion years old, which is less time (by several orders of magnitude, in some cases) than it takes for fusion to cease in such stars.

</p><p>Recent astrophysical models suggest that <a href="Red_dwarf" title="Red dwarf">red dwarfs</a> of 0.1 <var>M</var><sub>☉</sub> may stay on the main sequence for some six to twelve trillion years, gradually increasing in both <a href="Temperature" title="Temperature">temperature</a> and <a href="Luminosity" title="Luminosity">luminosity</a>, and take several hundred billion years more to collapse, slowly, into a <a href="White_dwarf" title="White dwarf">white dwarf</a>.<sup id="cite_ref-S&T_22_9-0" class="reference"><a href="#cite_note-S&T_22-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> Such stars will not become red giants as the whole star is a <a href="Convection_zone" title="Convection zone">convection zone</a> and it will not develop a degenerate helium core with a shell burning hydrogen. Instead, hydrogen fusion will proceed until almost the whole star is helium.

</p><p>Slightly more <a href="Massive_star" class="mw-redirect" title="Massive star">massive stars</a> do expand into <a href="Red_giant" title="Red giant">red giants</a>, but their helium cores are not massive enough to reach the temperatures required for helium fusion so they never reach the tip of the red-giant branch. When hydrogen shell burning finishes, these stars move directly off the red-giant branch like a post-<a href="Asymptotic_giant_branch" title="Asymptotic giant branch">asymptotic-giant-branch</a> (AGB) star, but at lower luminosity, to become a white dwarf.<sup id="cite_ref-endms_2-1" class="reference"><a href="#cite_note-endms-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> A star with an initial mass about 0.6 <var>M</var><sub>☉</sub> will be able to reach temperatures high enough to fuse helium, and these "mid-sized" stars go on to further stages of evolution beyond the red-giant branch.<sup id="cite_ref-lejeune_11-0" class="reference"><a href="#cite_note-lejeune-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Mid-sized_stars">Mid-sized stars</h3></div>

<p>Stars of roughly 0.6–10 <var>M</var><sub>☉</sub> become <a href="Red_giant" title="Red giant">red giants</a>, which are large non-<a href="Main_sequence" title="Main sequence">main-sequence</a> stars of <a href="Stellar_classification" title="Stellar classification">stellar classification</a> K or M. Red giants lie along the right edge of the Hertzsprung–Russell diagram due to their red color and large luminosity. Examples include <a href="Aldebaran" title="Aldebaran">Aldebaran</a> in the constellation <a href="Taurus_(constellation)" title="Taurus (constellation)">Taurus</a> and <a href="Arcturus" title="Arcturus">Arcturus</a> in the constellation of <a href="Bo%C3%B6tes" title="Boötes">Boötes</a>.

</p><p>Mid-sized stars are red giants during two different phases of their post-main-sequence evolution: red-giant-branch stars, with inert cores made of helium and hydrogen-burning shells, and asymptotic-giant-branch stars, with inert cores made of carbon and helium-burning shells inside the hydrogen-burning shells.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Between these two phases, stars spend a period on the <a href="Horizontal_branch" title="Horizontal branch">horizontal branch</a> with a helium-fusing core. Many of these helium-fusing stars cluster towards the cool end of the horizontal branch as K-type giants and are referred to as <a href="Red_clump" title="Red clump">red clump</a> giants.

</p>

<div class="mw-heading mw-heading4"><h4 id="Subgiant_phase">Subgiant phase</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Subgiant" title="Subgiant">Subgiant</a></div>

<p>When a star exhausts the hydrogen in its core, it leaves the main sequence and begins to fuse hydrogen in a shell outside the core. The core increases in mass as the shell produces more helium. Depending on the mass of the helium core, this continues for several million to one or two billion years, with the star expanding and cooling at a similar or slightly lower luminosity to its main sequence state. Eventually either the core becomes degenerate, in stars around the mass of the sun, or the outer layers cool sufficiently to become opaque, in more massive stars. Either of these changes cause the hydrogen shell to increase in temperature and the <a href="Luminosity" title="Luminosity">luminosity</a> of the star to increase, at which point the star expands onto the red-giant branch.<sup id="cite_ref-RyanNorton115_13-0" class="reference"><a href="#cite_note-RyanNorton115-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading4"><h4 id="Red-giant-branch_phase">Red-giant-branch phase</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Red-giant_branch" title="Red-giant branch">Red-giant branch</a></div>

<p>The expanding outer layers of the star are <a href="Convection" title="Convection">convective</a>, with the material being mixed by turbulence from near the fusing regions up to the surface of the star. For all but the lowest-mass stars, the fused material has remained deep in the stellar interior prior to this point, so the convecting envelope makes fusion products visible at the star's surface for the first time. At this stage of evolution, the results are subtle, with the largest effects, alterations to the <a href="Isotopes" class="mw-redirect" title="Isotopes">isotopes</a> of hydrogen and helium, being unobservable. The effects of the <a href="CNO_cycle" title="CNO cycle">CNO cycle</a> appear at the surface during the first <a href="Dredge-up" title="Dredge-up">dredge-up</a>, with lower <sup>12</sup>C/<sup>13</sup>C ratios and altered proportions of carbon and nitrogen. These are detectable with <a href="Spectroscopy" title="Spectroscopy">spectroscopy</a> and have been measured for many evolved stars.

</p><p>The helium core continues to grow on the red-giant branch. It is no longer in thermal equilibrium, either degenerate or above the <a href="Sch%C3%B6nberg%E2%80%93Chandrasekhar_limit" title="Schönberg–Chandrasekhar limit">Schönberg–Chandrasekhar limit</a>, so it increases in temperature which causes the rate of fusion in the hydrogen shell to increase. The star increases in luminosity towards the <a href="Tip_of_the_red-giant_branch" title="Tip of the red-giant branch">tip of the red-giant branch</a>. Red-giant-branch stars with a degenerate helium core all reach the tip with very similar core masses and very similar luminosities, although the more massive of the red giants become hot enough to ignite helium fusion before that point.

</p>

<div class="mw-heading mw-heading4"><h4 id="Horizontal_branch">Horizontal branch</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Main articles: <a href="Horizontal_branch" title="Horizontal branch">Horizontal branch</a> and <a href="Red_clump" title="Red clump">Red clump</a></div>

<p>In the helium cores of stars in the 0.6 to 2.0 solar mass range, which are largely supported by <a href="Electron_degeneracy_pressure" title="Electron degeneracy pressure">electron degeneracy pressure</a>, helium fusion will ignite on a timescale of days in a <a href="Helium_flash" title="Helium flash">helium flash</a>. In the nondegenerate cores of more massive stars, the ignition of helium fusion occurs relatively slowly with no flash.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> The nuclear power released during the helium flash is very large, on the order of 10<sup>8</sup> times the <a href="Solar_luminosity" title="Solar luminosity">luminosity of the Sun</a> for a few days<sup id="cite_ref-RyanNorton115_13-1" class="reference"><a href="#cite_note-RyanNorton115-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> and 10<sup>11</sup> times the luminosity of the Sun (roughly the luminosity of the <a href="Milky_Way_Galaxy" class="mw-redirect" title="Milky Way Galaxy">Milky Way Galaxy</a>) for a few seconds.<sup id="cite_ref-Prialnik151_15-0" class="reference"><a href="#cite_note-Prialnik151-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> However, the energy is consumed by the thermal expansion of the initially degenerate core and thus cannot be seen from outside the star.<sup id="cite_ref-RyanNorton115_13-2" class="reference"><a href="#cite_note-RyanNorton115-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Prialnik151_15-1" class="reference"><a href="#cite_note-Prialnik151-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Deupree1996_16-0" class="reference"><a href="#cite_note-Deupree1996-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> Due to the expansion of the core, the hydrogen fusion in the overlying layers slows and total energy generation decreases. The star contracts, although not all the way to the main sequence, and it migrates to the <a href="Horizontal_branch" title="Horizontal branch">horizontal branch</a> on the Hertzsprung–Russell diagram, gradually shrinking in radius and increasing its surface temperature.

</p>

<p>Core helium flash stars evolve to the red end of the horizontal branch but do not migrate to higher temperatures before they gain a degenerate carbon-oxygen core and start helium shell burning. These stars are often observed as a <a href="Red_clump" title="Red clump">red clump</a> of stars in the colour-magnitude diagram of a cluster, hotter and less luminous than the red giants. Higher-mass stars with larger helium cores move along the horizontal branch to higher temperatures, some becoming unstable pulsating stars in the yellow <a href="Instability_strip" title="Instability strip">instability strip</a> (<a href="RR_Lyrae_variables" class="mw-redirect" title="RR Lyrae variables">RR Lyrae variables</a>), whereas some become even hotter and can form a blue tail or blue hook to the horizontal branch. The morphology of the horizontal branch depends on parameters such as metallicity, age, and helium content, but the exact details are still being modelled.<sup id="cite_ref-parameters_17-0" class="reference"><a href="#cite_note-parameters-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading4"><h4 id="Asymptotic-giant-branch_phase">Asymptotic-giant-branch phase</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Asymptotic_giant_branch" title="Asymptotic giant branch">Asymptotic giant branch</a></div>

<p>After a star has consumed the helium at the core, hydrogen and helium fusion continues in shells around a hot core of <a href="Carbon" title="Carbon">carbon</a> and <a href="Oxygen" title="Oxygen">oxygen</a>. The star follows the <a href="Asymptotic_giant_branch" title="Asymptotic giant branch">asymptotic giant branch</a> on the Hertzsprung–Russell diagram, paralleling the original red-giant evolution, but with even faster energy generation (which lasts for a shorter time).<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> Although helium is being burnt in a shell, the majority of the energy is produced by hydrogen burning in a shell further from the core of the star. Helium from these hydrogen burning shells drops towards the center of the star and periodically the energy output from the helium shell increases dramatically. This is known as a <a href="Thermal_pulse" class="mw-redirect" title="Thermal pulse">thermal pulse</a> and they occur towards the end of the asymptotic-giant-branch phase, sometimes even into the post-asymptotic-giant-branch phase. Depending on mass and composition, there may be several to hundreds of thermal pulses.

</p><p>There is a phase on the ascent of the asymptotic-giant-branch where a deep convective zone forms and can bring carbon from the core to the surface. This is known as the second dredge up, and in some stars there may even be a third dredge up. In this way a <a href="Carbon_star" title="Carbon star">carbon star</a> is formed, very cool and strongly reddened stars showing strong carbon lines in their spectra. A process known as hot bottom burning may convert carbon into oxygen and nitrogen before it can be dredged to the surface, and the interaction between these processes determines the observed luminosities and spectra of carbon stars in particular clusters.<sup id="cite_ref-hbb_19-0" class="reference"><a href="#cite_note-hbb-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup>

</p><p>Another well known class of asymptotic-giant-branch stars is the <a href="Mira_variable" title="Mira variable">Mira variables</a>, which pulsate with well-defined periods of tens to hundreds of days and large amplitudes up to about 10 magnitudes (in the visual, total luminosity changes by a much smaller amount). In more-massive stars the stars become more luminous and the pulsation period is longer, leading to enhanced mass loss, and the stars become heavily obscured at visual wavelengths. These stars can be observed as <a href="OH/IR_star" title="OH/IR star">OH/IR stars</a>, pulsating in the infrared and showing OH <a href="Maser" title="Maser">maser</a> activity. These stars are clearly oxygen rich, in contrast to the carbon stars, but both must be produced by dredge ups.

</p>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Post-AGB" class="mw-redirect" title="Post-AGB">Post-AGB</a></div>

<p>These mid-range stars ultimately reach the tip of the asymptotic-giant-branch and run out of fuel for shell burning. They are not sufficiently massive to start full-scale carbon fusion, so they contract again, going through a period of post-asymptotic-giant-branch superwind to produce a planetary nebula with an extremely hot central star. The central star then cools to a white dwarf. The expelled gas is relatively rich in heavy elements created within the star and may be particularly <a href="Oxygen" title="Oxygen">oxygen</a> or <a href="Carbon" title="Carbon">carbon</a> enriched, depending on the type of the star. The gas builds up in an expanding shell called a <a href="Circumstellar_envelope" title="Circumstellar envelope">circumstellar envelope</a> and cools as it moves away from the star, allowing <a href="Circumstellar_dust" title="Circumstellar dust">dust particles</a> and molecules to form. With the high infrared energy input from the central star, ideal conditions are formed in these circumstellar envelopes for <a href="Astrophysical_maser" title="Astrophysical maser">maser</a> excitation.

</p><p>It is possible for thermal pulses to be produced once post-asymptotic-giant-branch evolution has begun, producing a variety of unusual and poorly understood stars known as born-again asymptotic-giant-branch stars.<sup id="cite_ref-bornagain_20-0" class="reference"><a href="#cite_note-bornagain-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> These may result in extreme <a href="Horizontal-branch" class="mw-redirect" title="Horizontal-branch">horizontal-branch</a> stars (<a href="Subdwarf_B_star" title="Subdwarf B star">subdwarf B stars</a>), hydrogen deficient post-asymptotic-giant-branch stars, variable planetary nebula central stars, and <a href="R_Coronae_Borealis_variable" title="R Coronae Borealis variable">R Coronae Borealis variables</a>.

</p>

<div class="mw-heading mw-heading3"><h3 id="Massive_stars">Massive stars</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Supergiant" title="Supergiant">Supergiant</a></div>

<p>In massive stars, the core is already large enough at the onset of the hydrogen burning shell that helium ignition will occur before electron degeneracy pressure has a chance to become prevalent. Thus, when these stars expand and cool, they do not brighten as dramatically as lower-mass stars; however, they were more luminous on the main sequence and they evolve to highly luminous supergiants. Their cores become massive enough that they cannot support themselves by <a href="Electron_degeneracy" class="mw-redirect" title="Electron degeneracy">electron degeneracy</a> and will eventually collapse to produce a <a href="Neutron_star" title="Neutron star">neutron star</a> or <a href="Black_hole" title="Black hole">black hole</a>.

</p>

<div class="mw-heading mw-heading4"><h4 id="Supergiant_evolution">Supergiant evolution</h4></div>

<p>Extremely massive stars (more than approximately 40 <var>M</var><sub>☉</sub>), which are very luminous and thus have very rapid stellar winds, lose mass so rapidly due to radiation pressure that they tend to strip off their own envelopes before they can expand to become <a href="Red_supergiant" title="Red supergiant">red supergiants</a>, and thus retain extremely high surface temperatures (and blue-white color) from their main-sequence time onwards. The largest stars of the current generation are about 100–150 <var>M</var><sub>☉</sub> because the outer layers would be expelled by the extreme radiation. Although lower-mass stars normally do not burn off their outer layers so rapidly, they can likewise avoid becoming red giants or red supergiants if they are in binary systems close enough so that the companion star strips off the envelope as it expands, or if they rotate rapidly enough so that convection extends all the way from the core to the surface, resulting in the absence of a separate core and envelope due to thorough mixing.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup>

</p>

<p>The core of a massive star, defined as the region depleted of hydrogen, grows hotter and denser as it accretes material from the fusion of hydrogen outside the core. In sufficiently massive stars, the core reaches temperatures and densities high enough to fuse carbon and heavier elements via the <a href="Alpha_process" title="Alpha process">alpha process</a>. At the end of helium fusion, the core of a star consists primarily of carbon and oxygen. In stars heavier than about 8 <var>M</var><sub>☉</sub>, the carbon ignites and <a href="Carbon-burning_process" title="Carbon-burning process">fuses</a> to form neon, sodium, and magnesium. Stars somewhat less massive may partially ignite carbon, but they are unable to fully fuse the carbon before <a href="Electron_degeneracy" class="mw-redirect" title="Electron degeneracy">electron degeneracy</a> sets in, and these stars will eventually leave an oxygen-neon-magnesium <a href="White_dwarf" title="White dwarf">white dwarf</a>.<sup id="cite_ref-jones_22-0" class="reference"><a href="#cite_note-jones-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-woosley_23-0" class="reference"><a href="#cite_note-woosley-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup>

</p><p>The exact mass limit for full carbon burning depends on several factors such as metallicity and the detailed mass lost on the <a href="Asymptotic_giant_branch" title="Asymptotic giant branch">asymptotic giant branch</a>, but is approximately 8–9 <var>M</var><sub>☉</sub>.<sup id="cite_ref-jones_22-1" class="reference"><a href="#cite_note-jones-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> After carbon burning is complete, the core of these stars reaches about 2.5 <var>M</var><sub>☉</sub> and becomes hot enough for heavier elements to fuse. Before oxygen starts to <a href="Oxygen-burning_process" title="Oxygen-burning process">fuse</a>, neon begins to <a href="Electron_capture" title="Electron capture">capture electrons</a> which triggers <a href="Neon-burning_process" title="Neon-burning process">neon burning</a>. For a range of stars of approximately 8-12 <var>M</var><sub>☉</sub>, this process is unstable and creates runaway fusion resulting in an <a href="Electron_capture_supernova" class="mw-redirect" title="Electron capture supernova">electron capture supernova</a>.<sup id="cite_ref-nomoto1987_24-0" class="reference"><a href="#cite_note-nomoto1987-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-woosley_23-1" class="reference"><a href="#cite_note-woosley-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup>

</p><p>In more massive stars, the fusion of neon proceeds without a runaway deflagration. This is followed in turn by complete oxygen burning and <a href="Silicon-burning_process" title="Silicon-burning process">silicon burning</a>, producing a core consisting largely of <a href="Iron-peak_element" class="mw-redirect" title="Iron-peak element">iron-peak elements</a>. Surrounding the core are shells of lighter elements still undergoing fusion. The timescale for complete fusion of a carbon core to an iron core is so short, just a few hundred years, that the outer layers of the star are unable to react and the appearance of the star is largely unchanged. The iron core grows until it reaches an <i>effective Chandrasekhar mass</i>, higher than the formal <a href="Chandrasekhar_mass" class="mw-redirect" title="Chandrasekhar mass">Chandrasekhar mass</a> due to various corrections for the relativistic effects, entropy, charge, and the surrounding envelope. The effective Chandrasekhar mass for an iron core varies from about 1.34 <var>M</var><sub>☉</sub> in the least massive red supergiants to more than 1.8 <var>M</var><sub>☉</sub> in more massive stars. Once this mass is reached, electrons begin to be captured into the iron-peak nuclei and the core becomes unable to support itself. The core collapses and the star is destroyed, either in a <a href="Supernova" title="Supernova">supernova</a> or direct collapse to a <a href="Black_hole" title="Black hole">black hole</a>.<sup id="cite_ref-woosley_23-2" class="reference"><a href="#cite_note-woosley-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading4"><h4 id="Supernova">Supernova</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Supernova" title="Supernova">Supernova</a></div>

<p>When the core of a massive star collapses, it will form a <a href="Neutron_star" title="Neutron star">neutron star</a>, or in the case of cores that exceed the <a href="Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit" title="Tolman–Oppenheimer–Volkoff limit">Tolman–Oppenheimer–Volkoff limit</a>, a <a href="Black_hole" title="Black hole">black hole</a>. Through a process that is not completely understood, some of the <a href="Gravitational_potential_energy" class="mw-redirect" title="Gravitational potential energy">gravitational potential energy</a> released by this core collapse is converted into a Type Ib, Type Ic, or Type II <a href="Supernova" title="Supernova">supernova</a>. It is known that the core collapse produces a massive surge of <a href="Neutrino" title="Neutrino">neutrinos</a>, as observed with supernova <a href="SN_1987A" title="SN 1987A">SN 1987A</a>. The extremely energetic <a href="Neutrinos" class="mw-redirect" title="Neutrinos">neutrinos</a> fragment some nuclei; some of their energy is consumed in releasing <a href="Nucleons" class="mw-redirect" title="Nucleons">nucleons</a>, including <a href="Neutrons" class="mw-redirect" title="Neutrons">neutrons</a>, and some of their energy is transformed into heat and <a href="Kinetic_energy" title="Kinetic energy">kinetic energy</a>, thus augmenting the <a href="Shock_wave" title="Shock wave">shock wave</a> started by rebound of some of the infalling material from the collapse of the core. Electron capture in very dense parts of the infalling matter may produce additional neutrons. Because some of the rebounding matter is bombarded by the neutrons, some of its nuclei capture them, creating a spectrum of heavier-than-iron material including the radioactive elements up to (and likely beyond) <a href="Uranium" title="Uranium">uranium</a>.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> Although non-exploding red giants can produce significant quantities of elements heavier than iron using neutrons released in side reactions of earlier <a href="Nuclear_reactions" class="mw-redirect" title="Nuclear reactions">nuclear reactions</a>, the abundance of elements heavier than <a href="Iron" title="Iron">iron</a> (and in particular, of certain isotopes of elements that have multiple stable or long-lived isotopes) produced in such reactions is quite different from that produced in a supernova. Neither abundance alone matches that found in the <a href="Solar_System" title="Solar System">Solar System</a>, so both supernovae, <a href="Neutron_star_merger" title="Neutron star merger">neutron star mergers</a><sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> and ejection of elements from red giants are required to explain the observed abundance of heavy elements and <a href="Isotopes" class="mw-redirect" title="Isotopes">isotopes</a> thereof.

</p><p>The energy transferred from collapse of the core to rebounding material not only generates heavy elements, but provides for their acceleration well beyond <a href="Escape_velocity" title="Escape velocity">escape velocity</a>, thus causing a Type Ib, Type Ic, or Type II supernova. Current understanding of this energy transfer is still not satisfactory; although current computer models of Type Ib, Type Ic, and Type II supernovae account for part of the energy transfer, they are not able to account for enough energy transfer to produce the observed ejection of material.<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> However, neutrino oscillations may play an important role in the energy transfer problem as they not only affect the energy available in a particular flavour of neutrinos but also through other general-relativistic effects on neutrinos.<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup>

</p><p>Some evidence gained from analysis of the mass and orbital parameters of binary neutron stars (which require two such supernovae) hints that the collapse of an oxygen-neon-magnesium core may produce a supernova that differs observably (in ways other than size) from a supernova produced by the collapse of an iron core.<sup id="cite_ref-30" class="reference"><a href="#cite_note-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup>

</p><p>The most massive stars that exist today may be completely destroyed by a supernova with an energy greatly exceeding its <a href="Gravitational_binding_energy" title="Gravitational binding energy">gravitational binding energy</a>. This rare event, caused by <a href="Pair-instability_supernova" title="Pair-instability supernova">pair-instability</a>, leaves behind no black hole remnant.<sup id="cite_ref-Hammer_31-0" class="reference"><a href="#cite_note-Hammer-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> In the past history of the universe, some stars were even larger than the largest that exists today, and they would immediately collapse into a black hole at the end of their lives, due to <a href="Photodisintegration" title="Photodisintegration">photodisintegration</a>.

</p>

<div class="mw-heading mw-heading2"><h2 id="Stellar_remnants">Stellar remnants</h2></div>

<p>After a star has burned out its fuel supply, its remnants can take one of three forms, depending on the mass during its lifetime.

</p>

<div class="mw-heading mw-heading3"><h3 id="White_and_black_dwarfs">White and black dwarfs</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main articles: <a href="White_dwarf" title="White dwarf">White dwarf</a> and <a href="Black_dwarf" title="Black dwarf">Black dwarf</a></div>

<p>For a star of 1 <var>M</var><sub>☉</sub>, the resulting white dwarf is of about 0.6 <var>M</var><sub>☉</sub>, compressed into approximately the volume of the Earth. White dwarfs are stable because the inward pull of gravity is balanced by the <a href="Degeneracy_pressure" class="mw-redirect" title="Degeneracy pressure">degeneracy pressure</a> of the star's electrons, a consequence of the <a href="Pauli_exclusion_principle" title="Pauli exclusion principle">Pauli exclusion principle</a>. Electron degeneracy pressure provides a rather soft limit against further compression; therefore, for a given chemical composition, white dwarfs of higher mass have a smaller volume. With no fuel left to burn, the star radiates its remaining heat into space for billions of years.

</p><p>A white dwarf is very hot when it first forms, more than 100,000 K at the surface and even hotter in its interior. It is so hot that a lot of its energy is lost in the form of neutrinos for the first 10 million years of its existence and will have lost most of its energy after a billion years.<sup id="cite_ref-32" class="reference"><a href="#cite_note-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup>

</p><p>The chemical composition of the white dwarf depends upon its mass. A star that has a mass of about 8-12 solar masses will ignite <a href="Carbon_burning_process" class="mw-redirect" title="Carbon burning process">carbon fusion</a> to form magnesium, neon, and smaller amounts of other elements, resulting in a white dwarf composed chiefly of oxygen, neon, and magnesium, provided that it can lose enough mass to get below the <a href="Chandrasekhar_limit" title="Chandrasekhar limit">Chandrasekhar limit</a> (see below), and provided that the ignition of carbon is not so violent as to blow the star apart in a supernova.<sup id="cite_ref-33" class="reference"><a href="#cite_note-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> A star of mass on the order of magnitude of the Sun will be unable to ignite carbon fusion, and will produce a white dwarf composed chiefly of carbon and oxygen, and of mass too low to collapse unless matter is added to it later (see below). A star of less than about half the mass of the Sun will be unable to ignite helium fusion (as noted earlier), and will produce a white dwarf composed chiefly of helium.

</p><p>In the end, all that remains is a cold dark mass sometimes called a <a href="Black_dwarf" title="Black dwarf">black dwarf</a>. However, the universe is not old enough for any black dwarfs to exist yet.

</p><p>If the white dwarf's mass increases above the <a href="Chandrasekhar_limit" title="Chandrasekhar limit">Chandrasekhar limit</a>, which is 1.4 <var>M</var><sub>☉</sub> for a white dwarf composed chiefly of carbon, oxygen, neon, and/or magnesium, then electron degeneracy pressure fails due to <a href="Electron_capture" title="Electron capture">electron capture</a> and the star collapses. Depending upon the chemical composition and pre-collapse temperature in the center, this will lead either to collapse into a <a href="Neutron_star" title="Neutron star">neutron star</a> or runaway ignition of carbon and oxygen. Heavier elements favor continued core collapse, because they require a higher temperature to ignite, because electron capture onto these elements and their fusion products is easier; higher core temperatures favor runaway nuclear reaction, which halts core collapse and leads to a <a href="Type_Ia_supernova" title="Type Ia supernova">Type Ia supernova</a>.<sup id="cite_ref-34" class="reference"><a href="#cite_note-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> These supernovae may be many times brighter than the Type II supernova marking the death of a massive star, even though the latter has the greater total energy release. This instability to collapse means that no white dwarf more massive than approximately 1.4 <var>M</var><sub>☉</sub> can exist (with a possible minor exception for very rapidly spinning white dwarfs, whose <a href="Centrifugal_force" title="Centrifugal force">centrifugal force</a> due to rotation partially counteracts the weight of their matter). Mass transfer in a <a href="Binary_system_(astronomy)" class="mw-redirect" title="Binary system (astronomy)">binary system</a> may cause an initially stable white dwarf to surpass the Chandrasekhar limit.

</p><p>If a white dwarf forms a close binary system with another star, hydrogen from the larger companion may accrete around and onto a white dwarf until it gets hot enough to fuse in a runaway reaction at its surface, although the white dwarf remains below the Chandrasekhar limit. Such an explosion is termed a <a href="Nova" title="Nova">nova</a>.

</p>

<div class="mw-heading mw-heading3"><h3 id="Neutron_stars">Neutron stars</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Neutron_star" title="Neutron star">Neutron star</a></div>

<p>Ordinarily, atoms are mostly electron clouds by volume, with very compact nuclei at the center (proportionally, if atoms were the size of a football stadium, their nuclei would be the size of dust mites). When a stellar core collapses, the pressure causes electrons and protons to fuse by <a href="Electron_capture" title="Electron capture">electron capture</a>. Without electrons, which keep nuclei apart, the neutrons collapse into a dense ball (in some ways like a giant <a href="Atomic_nucleus" title="Atomic nucleus">atomic nucleus</a>), with a thin overlying layer of <a href="Degenerate_matter" title="Degenerate matter">degenerate matter</a> (chiefly iron unless matter of different composition is added later). The neutrons resist further compression by the <a href="Pauli_exclusion_principle" title="Pauli exclusion principle">Pauli exclusion principle</a>, in a way analogous to electron degeneracy pressure, but stronger.

</p><p>These stars, known as neutron stars, are extremely small—on the order of radius 10 km, no bigger than the size of a large city—and are phenomenally dense. Their period of rotation shortens dramatically as the stars shrink (due to <a href="Conservation_of_angular_momentum" class="mw-redirect" title="Conservation of angular momentum">conservation of angular momentum</a>); observed rotational periods of neutron stars range from about 1.5 milliseconds (over 600 revolutions per second) to several seconds.<sup id="cite_ref-35" class="reference"><a href="#cite_note-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> When these rapidly rotating stars' magnetic poles are aligned with the Earth, we detect a pulse of radiation each revolution. Such neutron stars are called <a href="Pulsar" title="Pulsar">pulsars</a>, and were the first neutron stars to be discovered. Though electromagnetic radiation detected from pulsars is most often in the form of radio waves, pulsars have also been detected at visible, X-ray, and gamma ray wavelengths.<sup id="cite_ref-36" class="reference"><a href="#cite_note-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Black_holes">Black holes</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Black_hole" title="Black hole">Black hole</a></div>

<p>If the mass of the stellar remnant is high enough, the neutron degeneracy pressure will be insufficient to prevent collapse below the <a href="Schwarzschild_radius" title="Schwarzschild radius">Schwarzschild radius</a>. The stellar remnant thus becomes a black hole. The mass at which this occurs is not known with certainty, but is currently estimated at between 2 and 3 <var>M</var><sub>☉</sub>.

</p><p>Black holes are predicted by the theory of <a href="General_relativity" title="General relativity">general relativity</a>. According to classical general relativity, no matter or information can flow from the interior of a black hole to an outside observer, although <a href="Quantum_mechanics" title="Quantum mechanics">quantum effects</a> may allow deviations from this strict rule. The existence of black holes in the universe is well supported, both theoretically and by astronomical observation.

</p><p>Because the core-collapse mechanism of a supernova is, at present, only partially understood, it is still not known whether it is possible for a star to collapse directly to a black hole without producing a visible supernova, or whether some supernovae initially form unstable neutron stars which then collapse into black holes; the exact relation between the initial mass of the star and the final remnant is also not completely certain. Resolution of these uncertainties requires the analysis of more supernovae and supernova remnants.

</p>

<div class="mw-heading mw-heading2"><h2 id="Models">Models</h2></div>

<p>A stellar evolutionary model is a <a href="Mathematical_model" title="Mathematical model">mathematical model</a> that can be used to compute the evolutionary phases of a star from its formation until it becomes a remnant. The mass and chemical composition of the star are used as the inputs, and the luminosity and surface temperature are the only constraints. The model formulae are based upon the physical understanding of the star, usually under the assumption of hydrostatic equilibrium. Extensive computer calculations are then run to determine the changing state of the star over time, yielding a table of data that can be used to determine the <a href="Evolutionary_track" class="mw-redirect" title="Evolutionary track">evolutionary track</a> of the star across the <a href="Hertzsprung%E2%80%93Russell_diagram" title="Hertzsprung–Russell diagram">Hertzsprung–Russell diagram</a>, along with other evolving properties.<sup id="cite_ref-aass316_1_31_37-0" class="reference"><a href="#cite_note-aass316_1_31-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> Accurate models can be used to estimate the current age of a star by comparing its physical properties with those of stars along a matching evolutionary track.<sup id="cite_ref-ryan_norton2010_38-0" class="reference"><a href="#cite_note-ryan_norton2010-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup>

</p>

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<ul><li><a href="Compact_star" class="mw-redirect" title="Compact star">Compact star</a> – Classification of very high density object in astronomy</li>

<li><a href="Galaxy_formation_and_evolution" title="Galaxy formation and evolution">Galaxy formation and evolution</a> – Subfield of cosmology</li>

<li><a href="Chronology_of_the_universe" title="Chronology of the universe">Chronology of the universe</a> – History and future of the universe</li>

<li><a href="Nucleosynthesis" title="Nucleosynthesis">Nucleosynthesis</a> – Process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons</li>

<li><a href="Standard_solar_model" title="Standard solar model">Standard solar model</a> – Theoretical framework detailing the sun's structure, composition and energetics</li>

<li><a href="Stellar_population" title="Stellar population">Stellar population</a> – Grouping of stars by similar metallicity (<a href="Metallicity" title="Metallicity">metallicity</a>)</li>

<li><a href="Stellar_rotation#After_formation" title="Stellar rotation">Stellar rotation § After formation</a> – Angular motion of a star about its axis – Rotations slow as stars age</li>

<li><a href="Timeline_of_stellar_astronomy" title="Timeline of stellar astronomy">Timeline of stellar astronomy</a></li></ul>

</div>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<annotation encoding="application/x-tex">{\displaystyle (UBV)_{\mathsf {J}}(RI)_{\mathsf {C}}JHKLL'M}</annotation>

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<li id="cite_note-nomoto1987-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-nomoto1987_24-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFKen'ichi_Nomoto1987" class="citation journal cs1">Ken'ichi Nomoto (1987). "Evolution of 8–10 <var>M</var><sub>☉</sub> stars toward electron capture supernovae. II – Collapse of an O + Ne + Mg core". <i>Astrophysical Journal</i>. <b>322</b>: <span class="nowrap">206–</span>214. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1987ApJ...322..206N">1987ApJ...322..206N</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F165716">10.1086/165716</a>.</cite></span>

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<li id="cite_note-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-29">^</a></b></span> <span class="reference-text"><cite id="CITEREFYangKneller2017" class="citation journal cs1">Yang, Yue; Kneller, James P (2017). "GR effects in supernova neutrino flavor transformations". <i>Physical Review D</i>. <b>96</b> (2): 023009. <a href="ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/1705.09723">1705.09723</a></span>. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2017PhRvD..96b3009Y">2017PhRvD..96b3009Y</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1103%2FPhysRevD.96.023009">10.1103/PhysRevD.96.023009</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:119190550">119190550</a>.</cite></span>

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<li id="cite_note-30"><span class="mw-cite-backlink"><b><a href="#cite_ref-30">^</a></b></span> <span class="reference-text"><cite id="CITEREFE._P._J._van_den_Heuvel2004" class="citation journal cs1">E. P. J. van den Heuvel (2004). "X-Ray Binaries and Their Descendants: Binary Radio Pulsars; Evidence for Three Classes of Neutron Stars?". <i>Proceedings of the 5th INTEGRAL Workshop on the INTEGRAL Universe (ESA SP-552)</i>. <b>552</b>: <span class="nowrap">185–</span>194. <a href="ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/astro-ph/0407451">astro-ph/0407451</a></span>. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2004ESASP.552..185V">2004ESASP.552..185V</a>.</cite></span>

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<li id="cite_note-Hammer-31"><span class="mw-cite-backlink"><b><a href="#cite_ref-Hammer_31-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.mpa-garching.mpg.de/~hammer/lager/pair.pdf">Pair Instability Supernovae and Hypernovae.</a>, Nicolay J. Hammer, (2003), accessed May 7, 2007. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120608135141/http://www.mpa-garching.mpg.de/~hammer/lager/pair.pdf">Archived</a> June 8, 2012, at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a></span>

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<li id="cite_note-32"><span class="mw-cite-backlink"><b><a href="#cite_ref-32">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.vectorsite.net/tastgal_05.html">"Fossil Stars (1): White Dwarfs"</a>.</cite></span>

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<li id="cite_note-33"><span class="mw-cite-backlink"><b><a href="#cite_ref-33">^</a></b></span> <span class="reference-text"><cite id="CITEREFKen'ichi_Nomoto1984" class="citation journal cs1">Ken'ichi Nomoto (1984). <a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F161749">"Evolution of 8–10 <var>M</var><sub>☉</sub> stars toward electron capture supernovae. I – Formation of electron-degenerate O + Ne + Mg cores"</a>. <i>Astrophysical Journal</i>. <b>277</b>: <span class="nowrap">791–</span>805. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1984ApJ...277..791N">1984ApJ...277..791N</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F161749">10.1086/161749</a></span>.</cite></span>

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<li id="cite_note-34"><span class="mw-cite-backlink"><b><a href="#cite_ref-34">^</a></b></span> <span class="reference-text"><cite id="CITEREFKen'ichi_NomotoYoji_Kondo1991" class="citation journal cs1">Ken'ichi Nomoto & Yoji Kondo (1991). "Conditions for accretion-induced collapse of white dwarfs". <i>Astrophysical Journal</i>. <b>367</b>: <span class="nowrap">L19 –</span> <span class="nowrap">L22</span>. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1991ApJ...367L..19N">1991ApJ...367L..19N</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F185922">10.1086/185922</a>.</cite></span>

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<li id="cite_note-35"><span class="mw-cite-backlink"><b><a href="#cite_ref-35">^</a></b></span> <span class="reference-text"><cite id="CITEREFD'Amico,_N.Stappers,_B._W.Bailes,_M.Martin,_C._E.1998" class="citation journal cs1">D'Amico, N.; Stappers, B. W.; Bailes, M.; Martin, C. E.; Bell, J. F.; Lyne, A. G.; Manchester, R. N. (1998). <a rel="nofollow" class="external text" href="https://doi.org/10.1046%2Fj.1365-8711.1998.01397.x">"The Parkes Southern Pulsar Survey - III. Timing of long-period pulsars"</a>. <i>Monthly Notices of the Royal Astronomical Society</i>. <b>297</b> (1): <span class="nowrap">28–</span>40. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1998MNRAS.297...28D">1998MNRAS.297...28D</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1046%2Fj.1365-8711.1998.01397.x">10.1046/j.1365-8711.1998.01397.x</a></span>.</cite></span>

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</li>

<li id="cite_note-aass316_1_31-37"><span class="mw-cite-backlink"><b><a href="#cite_ref-aass316_1_31_37-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFDemarqueGuentherLiMazumdar2008" class="citation journal cs1">Demarque, P.; Guenther, D. B.; Li, L. H.; Mazumdar, A.; Straka, C. W. (August 2008). "YREC: the Yale rotating stellar evolution code". <i>Astrophysics and Space Science</i>. <b>316</b> (<span class="nowrap">1–</span>4): <span class="nowrap">31–</span>41. <a href="ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/0710.4003">0710.4003</a></span>. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2008Ap&SS.316...31D">2008Ap&SS.316...31D</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2Fs10509-007-9698-y">10.1007/s10509-007-9698-y</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9781402094408</bdi>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:14254892">14254892</a>.</cite></span>

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<li id="cite_note-ryan_norton2010-38"><span class="mw-cite-backlink"><b><a href="#cite_ref-ryan_norton2010_38-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFRyanNorton2010">Ryan & Norton (2010</a>, p. 79, "Assigning ages from hydrogen-burning timescales")</span>

</li>

</ol></div>

<ul><li><cite id="CITEREFHansenKawalerTrimble2004" class="citation book cs1">Hansen, Carl J.; Kawaler, Steven D.; Trimble, Virginia (2004). <i>Stellar interiors: physical principles, structure, and evolution</i> (2nd ed.). Springer-Verlag. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-387-20089-4</bdi>.</cite></li>

<li><cite id="CITEREFPrialnik2000" class="citation book cs1">Prialnik, Dina (2000). <i>An Introduction to the Theory of Stellar Structure and Evolution</i>. Cambridge University Press. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-521-65065-8</bdi>.</cite></li>

<li><cite id="CITEREFRyanNorton2010" class="citation book cs1">Ryan, Sean G.; Norton, Andrew J. (2010). <i>Stellar Evolution and Nucleosynthesis</i>. Cambridge University Press. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-521-13320-3</bdi>.</cite></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2></div>

<ul><li><cite id="CITEREFEkströmGeorgyEggenbergerMeynet2012" class="citation journal cs1">Ekström, S.; Georgy, C.; Eggenberger, P.; Meynet, G.; Mowlavi, N.; Wyttenbach, A.; Granada, A.; Decressin, T.; Hirschi, R.; Frischknecht, U.; Charbonnel, C.; Maeder, A. (2012). "Grids of stellar models with rotation". <i>Astronomy & Astrophysics</i>. <b>537</b>: A146. <a href="ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/1110.5049">1110.5049</a></span>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1051%2F0004-6361%2F201117751">10.1051/0004-6361/201117751</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:85458919">85458919</a>.</cite></li>

<li><a rel="nofollow" class="external text" href="http://www.astro.umd.edu/~miller/teaching/astr606/">Astronomy 606 (Stellar Structure and Evolution) lecture notes</a>, Cole Miller, Department of Astronomy, <a href="University_of_Maryland%2C_College_Park" title="University of Maryland, College Park">University of Maryland</a></li>

<li><a rel="nofollow" class="external text" href="http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/">Astronomy 162, Unit 2 (The Structure & Evolution of Stars) lecture notes</a>, Richard W. Pogge, Department of Astronomy, <a href="Ohio_State_University" title="Ohio State University">Ohio State University</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://spiff.rit.edu/classes/phys230/lectures/star_age/evol_hr.swf">Stellar evolution simulator</a></li>

<li><a rel="nofollow" class="external text" href="http://astro.df.unipi.it/stellar-models/">Pisa Stellar Models</a></li>

<li><a rel="nofollow" class="external text" href="https://mesa.sourceforge.net/">MESA stellar evolution codes (Modules for Experiments in Stellar Astrophysics)</a></li>

<li><a rel="nofollow" class="external text" href="https://www.bbc.co.uk/programmes/p00548w8">"The Life of Stars"</a>, BBC Radio 4 discussion with Paul Murdin, Janna Levin and Phil Charles (<i>In Our Time</i>, Mar. 27, 2003)</li>

<li>Life cycle of a star <a rel="nofollow" class="external autonumber" href="https://starinabox.lco.global/#">[1]</a> <a rel="nofollow" class="external autonumber" href="https://rainman.astro.illinois.edu/ddr/stellar/intermediate.html">[2]</a></li></ul>

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</style><div id="Stars520" style="font-size:114%;margin:0 4em"><a href="Star" title="Star">Stars</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Star_formation" title="Star formation">Formation</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Accretion_(astrophysics)" title="Accretion (astrophysics)">Accretion</a></li>

<li><a href="Molecular_cloud" title="Molecular cloud">Molecular cloud</a></li>

<li><a href="Bok_globule" title="Bok globule">Bok globule</a></li>

<li><a href="Young_stellar_object" title="Young stellar object">Young stellar object</a>

<ul><li><a href="Protostar" title="Protostar">Protostar</a></li>

<li><a href="Pre-main-sequence_star" title="Pre-main-sequence star">Pre-main-sequence</a></li>

<li><a href="Herbig_Ae/Be_star" title="Herbig Ae/Be star">Herbig Ae/Be</a></li>

<li><a href="T_Tauri_star" title="T Tauri star">T Tauri</a></li></ul></li>

<li><a href="Herbig%E2%80%93Haro_object" title="Herbig–Haro object">Herbig–Haro object</a></li>

<li><a href="Hayashi_track" title="Hayashi track">Hayashi track</a></li>

<li><a href="Henyey_track" title="Henyey track">Henyey track</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Main_sequence" title="Main sequence">Main sequence</a></li>

<li><a href="Red-giant_branch" title="Red-giant branch">Red-giant branch</a></li>

<li><a href="Horizontal_branch" title="Horizontal branch">Horizontal branch</a>

<ul><li><a href="Red_clump" title="Red clump">Red clump</a></li></ul></li>

<li><a href="Asymptotic_giant_branch" title="Asymptotic giant branch">Asymptotic giant branch</a>

<li><a href="Super-AGB_star" title="Super-AGB star">super-AGB</a></li></ul></li>

<li><a href="Planetary_nebula" title="Planetary nebula">Planetary nebula</a>

<ul><li><a href="Protoplanetary_nebula" title="Protoplanetary nebula">Protoplanetary</a></li></ul></li>

<li><a href="Wolf%E2%80%93Rayet_nebula" title="Wolf–Rayet nebula">Wolf–Rayet nebula</a></li>

<li><a href="Dredge-up" title="Dredge-up">Dredge-up</a></li>

<li><a href="Instability_strip" title="Instability strip">Instability strip</a></li>

<li><a href="Luminous_blue_variable" title="Luminous blue variable">Luminous blue variable</a></li>

<li><a href="Stellar_population" title="Stellar population">Stellar population</a></li>

<li><a href="Supernova" title="Supernova">Supernova</a>

<ul><li><a href="Superluminous_supernova" title="Superluminous supernova">Superluminous</a></li>

<li><a href="Hypernova" title="Hypernova">Hypernova</a></li></ul></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Stellar_classification" title="Stellar classification">Classification</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Early-type_star" class="mw-redirect" title="Early-type star">Early</a></li>

<li>Main sequence

<li><a href="Subdwarf" title="Subdwarf">Subdwarf</a>

<li><a href="Subgiant" title="Subgiant">Subgiant</a></li>

<li><a href="Giant_star" title="Giant star">Giant</a>

<li><a href="Yellow_giant" class="mw-redirect" title="Yellow giant">Yellow</a></li></ul></li>

<li><a href="Bright_giant" class="mw-redirect" title="Bright giant">Bright giant</a></li>

<li><a href="Supergiant" title="Supergiant">Supergiant</a>

<li><a href="Yellow_supergiant" title="Yellow supergiant">Yellow</a></li></ul></li>

<li><a href="Hypergiant" title="Hypergiant">Hypergiant</a>

<ul><li><a href="Yellow_hypergiant" title="Yellow hypergiant">Yellow</a></li></ul></li>

<li><a href="Carbon_star" title="Carbon star">Carbon</a>

<li><a href="White_dwarf" title="White dwarf">White dwarf</a></li>

<li><a href="Chemically_peculiar_star" title="Chemically peculiar star">Chemically peculiar</a>

<li><a href="Barium_star" title="Barium star">Barium</a></li>

<li><a href="Lambda_Bo%C3%B6tis_star" title="Lambda Boötis star">Lambda Boötis</a></li>

<li><a href="Technetium_star" title="Technetium star">Technetium</a></li></ul></li>

<ul><li><a href="Shell_star" title="Shell star">Shell</a></li></ul></li>

<li><a href="Helium_star" title="Helium star">Helium</a>

<ul><li><a href="Extreme_helium_star" title="Extreme helium star">Extreme</a></li></ul></li>

<li><a href="Blue_straggler" title="Blue straggler">Blue straggler</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Compact_star" class="mw-redirect" title="Compact star">Remnants</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Compact_star" class="mw-redirect" title="Compact star">Compact star</a></li>

<li><a href="IRAS_00500%2B6713" title="IRAS 00500+6713">Parker's star</a></li>

<li><a href="White_dwarf" title="White dwarf">White dwarf</a>

<ul><li><a href="Helium_planet" title="Helium planet">Helium planet</a></li></ul></li>

<li><a href="Neutron_star" title="Neutron star">Neutron</a>

<ul><li><a href="Radio-quiet_neutron_star" title="Radio-quiet neutron star">Radio-quiet</a></li>

<li><a href="Pulsar" title="Pulsar">Pulsar</a>

<ul><li><a href="Binary_pulsar" title="Binary pulsar">Binary</a></li>

<li><a href="Magnetar" title="Magnetar">Magnetar</a></li></ul></li>

<li><a href="Stellar_black_hole" title="Stellar black hole">Stellar black hole</a></li>

<li><a href="X-ray_binary" title="X-ray binary">X-ray binary</a>

<ul><li><a href="X-ray_burster" title="X-ray burster">Burster</a></li></ul></li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Hypothetical_star" title="Hypothetical star">Hypothetical</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Blue_dwarf_(red-dwarf_stage)" title="Blue dwarf (red-dwarf stage)">Blue dwarf</a></li>

<li><a href="Black_dwarf" title="Black dwarf">Black dwarf</a></li>

<li><a href="Exotic_star" title="Exotic star">Exotic</a>

<ul><li><a href="Boson_star" class="mw-redirect" title="Boson star">Boson</a></li>

<li><a href="Electroweak_star" class="mw-redirect" title="Electroweak star">Electroweak</a></li>

<li><a href="Strange_star" title="Strange star">Strange</a></li>

<li><a href="Preon_star" class="mw-redirect" title="Preon star">Preon</a></li>

<li><a href="Planck_star" title="Planck star">Planck</a></li>

<li><a href="Dark-energy_star" title="Dark-energy star">Dark-energy</a></li>

<li><a href="Quark_star" title="Quark star">Quark</a></li>

<li>Black hole star

<ul><li><a href="Black_star_(semiclassical_gravity)" title="Black star (semiclassical gravity)">Black</a></li>

<li>Hawking</li>

<li><a href="Quasi-star" title="Quasi-star">Quasi-star</a></li></ul></li>

<li><a href="Gravastar" title="Gravastar">Gravastar</a></li>

<li><a href="Thorne%E2%80%93%C5%BBytkow_object" title="Thorne–Żytkow object">Thorne–Żytkow object</a></li>

<li><a href="Blitzar" title="Blitzar">Blitzar</a></li>

<li><a href="White_hole" title="White hole">White hole</a></li></ul>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Stellar_nucleosynthesis" title="Stellar nucleosynthesis">Nucleosynthesis</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Deuterium_fusion" title="Deuterium fusion">Deuterium burning</a></li>

<li><a href="Lithium_burning" title="Lithium burning">Lithium burning</a></li>

<li><a href="Proton%E2%80%93proton_chain" title="Proton–proton chain">Proton–proton chain</a></li>

<li><a href="CNO_cycle" title="CNO cycle">CNO cycle</a></li>

<li><a href="Helium_flash" title="Helium flash">Helium flash</a></li>

<li><a href="Triple-alpha_process" title="Triple-alpha process">Triple-alpha process</a></li>

<li><a href="Alpha_process" title="Alpha process">Alpha process</a></li>

<li><a href="Carbon-burning_process" title="Carbon-burning process">C burning</a></li>

<li><a href="Neon-burning_process" title="Neon-burning process">Ne burning</a></li>

<li><a href="Oxygen-burning_process" title="Oxygen-burning process">O burning</a></li>

<li><a href="Silicon-burning_process" title="Silicon-burning process">Si burning</a></li>

<li><a href="S-process" title="S-process">s-process</a></li>

<li><a href="R-process" title="R-process">r-process</a></li>

<li><a href="P-process" title="P-process">p-process</a></li>

<ul><li><a href="Symbiotic_nova" title="Symbiotic nova">Symbiotic</a></li>

<li><a href="Nova_remnant" title="Nova remnant">Remnant</a></li>

<li><a href="Luminous_red_nova" title="Luminous red nova">Luminous red nova</a></li>

<li><a href="Nova#Recurrent_novae" title="Nova">Recurrent</a></li>

<li><a href="Micronova" title="Micronova">Micronova</a></li></ul></li>

<li><a href="Supernova_nucleosynthesis" title="Supernova nucleosynthesis">Supernova</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Stellar_structure" title="Stellar structure">Structure</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="Convection_zone" title="Convection zone">Convection zone</a>

<ul><li><a href="Microturbulence" title="Microturbulence">Microturbulence</a></li>

<li><a href="Solar-like_oscillations" title="Solar-like oscillations">Oscillations</a></li></ul></li>

<li><a href="Radiation_zone" class="mw-redirect" title="Radiation zone">Radiation zone</a></li>

<li><a href="Stellar_atmosphere" title="Stellar atmosphere">Atmosphere</a>

<ul><li><a href="Photosphere" title="Photosphere">Photosphere</a></li>

<li><a href="Starspot" title="Starspot">Starspot</a></li>

<li><a href="Chromosphere" title="Chromosphere">Chromosphere</a></li>

<li><a href="Stellar_corona" title="Stellar corona">Stellar corona</a></li>

<li><a href="Alfv%C3%A9n_surface" title="Alfvén surface">Alfvén surface</a></li></ul></li>

<li><a href="Stellar_wind" title="Stellar wind">Stellar wind</a>

<ul><li><a href="Stellar-wind_bubble" title="Stellar-wind bubble">Bubble</a></li>

<li><a href="Bipolar_outflow" title="Bipolar outflow">Bipolar outflow</a></li></ul></li>

<li><a href="Accretion_disk" title="Accretion disk">Accretion disk</a>

<ul><li><a href="Protoplanetary_disk" title="Protoplanetary disk">Protoplanetary disk</a></li>

<li><a href="Proplyd" title="Proplyd">Proplyd</a></li></ul></li>

<li><a href="Asteroseismology" title="Asteroseismology">Asteroseismology</a>

<ul><li><a href="Helioseismology" title="Helioseismology">Helioseismology</a></li></ul></li>

<li><a href="Circumstellar_dust" title="Circumstellar dust">Circumstellar dust</a></li>

<li><a href="Cosmic_dust" title="Cosmic dust">Cosmic dust</a></li>

<li><a href="Circumstellar_envelope" title="Circumstellar envelope">Circumstellar envelope</a></li>

<li><a href="Eddington_luminosity" title="Eddington luminosity">Eddington luminosity</a></li>

<li><a href="Kelvin%E2%80%93Helmholtz_mechanism" title="Kelvin–Helmholtz mechanism">Kelvin–Helmholtz mechanism</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Properties</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Stellar_designations_and_names" title="Stellar designations and names">Designation</a></li>

<li><a href="Stellar_dynamics" title="Stellar dynamics">Dynamics</a></li>

<li><a href="Effective_temperature" title="Effective temperature">Effective temperature</a></li>

<li><a href="Luminosity" title="Luminosity">Luminosity</a></li>

<li><a href="Stellar_kinematics" title="Stellar kinematics">Kinematics</a></li>

<li><a href="Stellar_magnetic_field" title="Stellar magnetic field">Magnetic field</a></li>

<li><a href="Absolute_magnitude" title="Absolute magnitude">Absolute magnitude</a></li>

<li><a href="Metallicity" title="Metallicity">Metallicity</a></li>

<li><a href="Stellar_rotation" title="Stellar rotation">Rotation</a>

<ul><li><a href="Gravity_darkening" title="Gravity darkening">Gravity darkening</a></li></ul></li>

<li><a href="Starlight" title="Starlight">Starlight</a></li>

<li><a href="Variable_star" title="Variable star">Variable</a></li>

<li><a href="Photometric_system" title="Photometric system">Photometric system</a></li>

<li><a href="Color_index" title="Color index">Color index</a></li>

<li><a href="Hertzsprung%E2%80%93Russell_diagram" title="Hertzsprung–Russell diagram">Hertzsprung–Russell diagram</a></li>

<li><a href="Color%E2%80%93color_diagram" title="Color–color diagram">Color–color diagram</a></li>

<li><a href="Str%C3%B6mgren_sphere" title="Strömgren sphere">Strömgren sphere</a></li>

<li><a href="Kraft_break" title="Kraft break">Kraft break</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Star_system" title="Star system">Star systems</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Binary_star" title="Binary star">Binary</a>

<ul><li><a href="Contact_binary" title="Contact binary">Contact</a></li>

<li><a href="Common_envelope" title="Common envelope">Common envelope</a></li>

<li><a href="Eclipsing_binary" class="mw-redirect" title="Eclipsing binary">Eclipsing</a></li>

<li><a href="Symbiotic_binary" title="Symbiotic binary">Symbiotic</a></li></ul></li>

<li><a href="Star_system#Multiple_star_systems" title="Star system">Multiple</a></li>

<li><a href="Star_cluster" title="Star cluster">Cluster</a>

<li><a href="Globular_cluster" title="Globular cluster">Globular</a></li>

<li><a href="Super_star_cluster" title="Super star cluster">Super</a></li></ul></li>

<li><a href="Planetary_system" title="Planetary system">Planetary system</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Earth-centric<br>observations</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Solar_eclipse" title="Solar eclipse">Solar eclipse</a></li>

<li><a href="Solar_radio_emission" title="Solar radio emission">Solar radio emission</a></li>

<li><a href="Solar_System" title="Solar System">Solar System</a></li>

<li><a href="Sunlight" title="Sunlight">Sunlight</a></li></ul></li>

<li><a href="Circumpolar_star" title="Circumpolar star">Circumpolar</a></li>

<li><a href="Constellation" title="Constellation">Constellation</a></li>

<li><a href="Asterism_(astronomy)" title="Asterism (astronomy)">Asterism</a></li>

<li><a href="Magnitude_(astronomy)" title="Magnitude (astronomy)">Magnitude</a>

<ul><li><a href="Apparent_magnitude" title="Apparent magnitude">Apparent</a></li>

<li><a href="Extinction_(astronomy)" title="Extinction (astronomy)">Extinction</a></li>

<li><a href="Photographic_magnitude" title="Photographic magnitude">Photographic</a></li></ul></li>

<li><a href="Radial_velocity" title="Radial velocity">Radial velocity</a></li>

<li><a href="Proper_motion" title="Proper motion">Proper motion</a></li>

<li><a href="Stellar_parallax" title="Stellar parallax">Parallax</a></li>

<li><a href="Photometric-standard_star" title="Photometric-standard star">Photometric-standard</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Lists_of_stars" title="Lists of stars">Lists</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="List_of_proper_names_of_stars" title="List of proper names of stars">Proper names</a>

<ul><li><a href="List_of_Arabic_star_names" title="List of Arabic star names">Arabic</a></li>

<li><a href="Chinese_star_names" class="mw-redirect" title="Chinese star names">Chinese</a></li></ul></li>

<li><a href="List_of_star_extremes" title="List of star extremes">Extremes</a>

<ul><li><a href="List_of_most_massive_stars" title="List of most massive stars">Most massive</a></li>

<li><a href="List_of_hottest_stars" title="List of hottest stars">Highest temperature</a></li>

<li><a href="List_of_coolest_stars" title="List of coolest stars">Lowest temperature</a></li>

<li><a href="List_of_largest_stars" title="List of largest stars">Largest volume</a></li>

<li><a href="List_of_smallest_known_stars" title="List of smallest known stars">Smallest volume</a></li>

<li><a href="List_of_brightest_stars" title="List of brightest stars">Brightest</a></li>

<li><a href="Historical_brightest_stars" title="Historical brightest stars">Historical brightest</a></li>

<li><a href="List_of_most_luminous_stars" title="List of most luminous stars">Most luminous</a></li>

<li><a href="List_of_nearest_stars" title="List of nearest stars">Nearest</a>

<ul><li><a href="List_of_nearest_bright_stars" title="List of nearest bright stars">bright</a></li></ul></li></ul></li>

<li><a href="List_of_most_distant_stars" title="List of most distant stars">Most distant</a></li>

<li><a href="List_of_stars_with_resolved_images" title="List of stars with resolved images">With resolved images</a></li>

<li><a href="List_of_multiplanetary_systems" title="List of multiplanetary systems">With multiple exoplanets</a></li>

<li><a href="List_of_brown_dwarfs" title="List of brown dwarfs">Brown dwarfs</a></li>

<li><a href="List_of_red_dwarfs" title="List of red dwarfs">Red dwarfs</a></li>

<li><a href="List_of_white_dwarfs" title="List of white dwarfs">White dwarfs</a></li>

<li><a href="List_of_novae_in_the_Milky_Way_galaxy" title="List of novae in the Milky Way galaxy">Milky Way novae</a></li>

<li><a href="List_of_supernovae" title="List of supernovae">Supernovae</a>

<ul><li><a href="List_of_supernova_candidates" title="List of supernova candidates">Candidates</a></li>

<li><a href="List_of_supernova_remnants" title="List of supernova remnants">Remnants</a></li></ul></li>

<li><a href="List_of_planetary_nebulae" title="List of planetary nebulae">Planetary nebulae</a></li>

<li><a href="Timeline_of_stellar_astronomy" title="Timeline of stellar astronomy">Timeline of stellar astronomy</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Substellar_object" title="Substellar object">Substellar object</a>

<ul><li><a href="Brown_dwarf" title="Brown dwarf">Brown dwarf</a>

<ul><li><a href="Brown-dwarf_desert" title="Brown-dwarf desert">Desert</a></li>

<li><a href="Planet" title="Planet">Planet</a></li></ul></li>

<li><a href="Galactic_year" title="Galactic year">Galactic year</a></li>

<li><a href="Galaxy" title="Galaxy">Galaxy</a></li>

<li><a href="Guest_star_(astronomy)" title="Guest star (astronomy)">Guest</a></li>

<li><a href="Gravity" title="Gravity">Gravity</a></li>

<li><a href="Intergalactic_star" title="Intergalactic star">Intergalactic</a></li>

<li><a href="Neutron_star_merger" title="Neutron star merger">Neutron star merger</a></li>

<li><a href="Planet-hosting_stars" class="mw-redirect" title="Planet-hosting stars">Planet-hosting stars</a></li>

<li><a href="Stellar_collision" title="Stellar collision">Stellar collision</a></li>

<li><a href="Stellar_engulfment" title="Stellar engulfment">Stellar engulfment</a></li>

<li><a href="Tidal_disruption_event" title="Tidal disruption event">Tidal disruption event</a></li></ul>

</div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div>

<ul><li><span class="noviewer" typeof="mw:File"><span title="Category"></span></span> Category</li>

<li><span class="nowrap"><span class="noviewer" typeof="mw:File"></span> </span><a href="Portal%3AStars" title="Portal:Stars">Stars portal</a></li></ul>

</div></td></tr></tbody></table></div>

<div class="navbox-styles"></div><div role="navigation" class="navbox" aria-labelledby="Big_History90" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2" style="text-align:center;"><div id="Big_History90" style="font-size:114%;margin:0 4em"><a href="Big_History" title="Big History">Big History</a></div></th></tr><tr><th scope="row" class="navbox-group" style="text-align:center;;width:1%">Themes and subjects</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Chronology_of_the_universe" title="Chronology of the universe">Chronology of the universe</a></li>

<li><a href="Physical_cosmology" title="Physical cosmology">Cosmic evolution</a></li>

<li><a href="Geologic_time_scale" title="Geologic time scale">Time scales</a></li>

<li><a href="Goldilocks_principle" title="Goldilocks principle">Goldilocks principle</a></li>

<li><a href="Modernity" title="Modernity">Modernity</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="text-align:center;;width:1%">Eight thresholds</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li>1: <b>Creation</b> - <a href="Big_Bang" title="Big Bang">Big Bang</a> and <a href="Cosmogony" title="Cosmogony">cosmogony</a></li>

<li>2: <b>Stars</b> - <a href="Star#Formation_and_evolution" title="Star">creation of stars</a></li>

<li>3: <b>Elements</b> - <a href="Stellar_nucleosynthesis" title="Stellar nucleosynthesis">creation of chemical elements</a> inside </li>

<li>4: <b>Planets</b> - <a href="Nebular_hypothesis" title="Nebular hypothesis">formation of planets</a></li>

<li>5: <b>Life</b> - <a href="Abiogenesis" title="Abiogenesis">abiogenesis</a> and <a href="Evolution" title="Evolution">evolution of life</a></li>

<li>6: <b>Humans</b> - development of <i><a href="Human_evolution" title="Human evolution">Homo sapiens</a></i>

<ul><li><a href="Prehistory" title="Prehistory">Stone Age</a></li></ul></li>

<li>7: <b>Agriculture</b> - <a href="Neolithic_Revolution" title="Neolithic Revolution">Agricultural Revolution</a></li>

<li>8: <b>Modernity</b> - <a href="Modern_history" class="mw-redirect" title="Modern history">modern era</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="text-align:center;;width:1%">Web-based education</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="OER_Project" title="OER Project">Big History Project</a></li>

<li><a href="ChronoZoom" title="ChronoZoom">ChronoZoom</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="text-align:center;;width:1%">Notable people</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Walter_Alvarez" title="Walter Alvarez">Walter Alvarez</a></li>

<li><a href="Cynthia_Stokes_Brown" title="Cynthia Stokes Brown">Cynthia Stokes Brown</a></li>

<li><a href="Eric_Chaisson" title="Eric Chaisson">Eric Chaisson</a></li>

<li><a href="David_Christian_(historian)" title="David Christian (historian)">David Christian</a></li>

<li><a href="Carl_Sagan" title="Carl Sagan">Carl Sagan</a></li>

<li><a href="Graeme_Snooks" title="Graeme Snooks">Graeme Snooks</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="text-align:center;;width:1%">Related</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="Big_History_(TV_series)" title="Big History (TV series)">Big History</a></i> (2013 series)</li></ul>

</div></td></tr></tbody></table></div>

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</style></div><div role="navigation" class="navbox authority-control" aria-labelledby="Authority_control_databases_frameless&#124;text-top&#124;10px&#124;alt=Edit_this_at_Wikidata&#124;link=https&#58;//www.wikidata.org/wiki/Q6472#identifiers&#124;class=noprint&#124;Edit_this_at_Wikidata1295" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Authority_control_databases_frameless&#124;text-top&#124;10px&#124;alt=Edit_this_at_Wikidata&#124;link=https&#58;//www.wikidata.org/wiki/Q6472#identifiers&#124;class=noprint&#124;Edit_this_at_Wikidata1295" style="font-size:114%;margin:0 4em">Authority control databases </div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">National</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"><ul><li><span class="uid"><span class="rt-commentedText tooltip tooltip-dotted" title="Sternentwicklung"><a rel="nofollow" class="external text" href="https://d-nb.info/gnd/4057365-5">Germany</a></span></span></li><li><span class="uid"><span class="rt-commentedText tooltip tooltip-dotted" title="Stars--Evolution"><a rel="nofollow" class="external text" href="https://id.loc.gov/authorities/sh85127430">United States</a></span></span></li><li><span class="uid"><span class="rt-commentedText tooltip tooltip-dotted" title="Zvaigžņu evolūcija"><a rel="nofollow" class="external text" href="https://kopkatalogs.lv/F?func=direct&local_base=lnc10&doc_number=000150010&P_CON_LNG=ENG">Latvia</a></span></span></li><li><span class="uid"><a rel="nofollow" class="external text" href="https://www.nli.org.il/en/authorities/987007531590905171">Israel</a></span></li></ul></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"><ul><li><span class="uid"><a rel="nofollow" class="external text" href="https://lux.collections.yale.edu/view/concept/8e1b5fd7-f39d-430d-8ba6-d5b99f762604">Yale LUX</a></span></li></ul></div></td></tr></tbody></table></div></div><div><div class="zim-footer">

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