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In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926.^[1]

Baade observed that bluer stars were strongly associated with the spiral arms, and yellow stars dominated near the central galactic bulge and within globular star clusters.^[2] Two main divisions were defined as Population I star and population II, with another newer, hypothetical division called population III added in 1978.

Among the population types, significant differences were found with their individual observed stellar spectra. These were later shown to be very important and were possibly related to star formation, observed kinematics,^[3] stellar age, and even galaxy evolution in both spiral and elliptical galaxies. These three simple population classes usefully divided stars by their chemical composition or metallicity.^[4]^[5]^[3]

By definition, each population group shows the trend where lower metal content indicates higher age of stars. Hence, the first stars in the universe (very low metal content) were deemed population III, old stars (low metallicity) as population II, and recent stars (high metallicity) as population I.^[6] The Sun is considered population I, a recent star with a relatively high 1.4% metallicity. Note that astrophysics nomenclature considers any element heavier than helium to be a "metal", including chemical non-metals such as oxygen.^[7]

Stellar development

Observation of stellar spectra has revealed that stars older than the Sun have fewer heavy elements compared with the Sun.^[3] This immediately suggests that metallicity has evolved through the generations of stars by the process of stellar nucleosynthesis.

Formation of the first stars

Under current cosmological models, all matter created in the Big Bang was mostly hydrogen (75%) and helium (25%), with only a very tiny fraction consisting of other light elements such as lithium and beryllium.^[8] When the universe had cooled sufficiently, the first stars were born as population III stars, without any contaminating heavier metals. This is postulated to have affected their structure so that their stellar masses became hundreds of times more than that of the Sun. In turn, these massive stars also evolved very quickly, and their nucleosynthetic processes created the first 26 elements (up to iron in the periodic table).^[9]

Many theoretical stellar models show that most high-mass population III stars rapidly exhausted their fuel and likely exploded in extremely energetic pair-instability supernovae. Those explosions would have thoroughly dispersed their material, ejecting metals into the interstellar medium (ISM), to be incorporated into the later generations of stars. Their destruction suggests that no galactic high-mass population III stars should be observable.^[10] However, some population III stars might be seen in high-redshift galaxies whose light originated during the earlier history of the universe.^[11] Scientists have found evidence of an extremely small ultra metal-poor star, slightly smaller than the Sun, found in a binary system of the spiral arms in the Milky Way. The discovery opens up the possibility of observing even older stars.^[12]

Stars too massive to produce pair-instability supernovae would have likely collapsed into black holes through a process known as photodisintegration. Here some matter may have escaped during this process in the form of relativistic jets, and this could have distributed the first metals into the universe.^[13]^[14]^[a]

Formation of the observed stars

The oldest stars observed thus far,^[10] known as population II, have very low metallicities;^[16]^[6] as subsequent generations of stars were born, they became more metal-enriched, as the gaseous clouds from which they formed received the metal-rich dust manufactured by previous generations of stars from population III.

As those population II stars died, they returned metal-enriched material to the interstellar medium via planetary nebulae and supernovae, enriching further the nebulae, out of which the newer stars formed. These youngest stars, including the Sun, therefore have the highest metal content, and are known as population I stars.

Chemical classification by Walter Baade

Population I stars

Population I star Rigel with reflection nebula IC 2118

Population I stars are young stars with the highest metallicity out of all three populations and are more commonly found in the spiral arms of the Milky Way galaxy. The Sun is considered as an intermediate population I star, while the sun-like $μ$ Arae is much richer in metals.^[17] (The term "metal rich star" is used to describe stars with a significantly higher metallicity than the Sun; higher than can be explained by measurement error.)

Population I stars usually have regular elliptical orbits of the Galactic Center, with a low relative velocity. It was earlier hypothesized that the high metallicity of population I stars makes them more likely to possess planetary systems than the other two populations, because planets, particularly terrestrial planets, are thought to be formed by the accretion of metals.^[18] However, observations of the Kepler Space Telescope data have found smaller planets around stars with a range of metallicities, while only larger, potential gas giant planets are concentrated around stars with relatively higher metallicity – a finding that has implications for theories of gas-giant formation.^[19] Between the intermediate population I and the population II stars comes the intermediate disc population.

Population II stars

Population II, or metal-poor, stars are those with relatively little of the elements heavier than helium. These objects were formed during an earlier time of the universe. Intermediate population II stars are common in the bulge near the centre of the Milky Way, whereas population II stars found in the galactic halo are older and thus more metal-deficient. Globular clusters also contain high numbers of population II stars.^[20]

A characteristic of population II stars is that despite their lower overall metallicity, they often have a higher ratio of "alpha elements" (elements produced by the alpha process, like oxygen and neon) relative to iron (Fe) as compared with population I stars; current theory suggests that this is the result of type II supernovas being more important contributors to the interstellar medium at the time of their formation, whereas type Ia supernova metal-enrichment came at a later stage in the universe's development.^[21]

Scientists have targeted these oldest stars in several different surveys, including the HK objective-prism survey of Timothy C. Beers et al.^[22] and the Hamburg-ESO survey of Norbert Christlieb et al.,^[23] originally started for faint quasars. Thus far, they have uncovered and studied in detail about ten ultra-metal-poor (UMP) stars (such as Sneden's Star, Cayrel's Star, BD +17° 3248) and three of the oldest stars known to date: HE 0107-5240, HE 1327-2326 and HE 1523-0901. Caffau's star was identified as the most metal-poor star yet when it was found in 2012 using Sloan Digital Sky Survey data. However, in February 2014 the discovery of an even lower-metallicity star was announced, SMSS J031300.36-670839.3 located with the aid of SkyMapper astronomical survey data. Less extreme in their metal deficiency, but nearer and brighter and hence longer known, are HD 122563 (a red giant) and HD 140283 (a subgiant).

Population III stars

Population III stars^[24] are a hypothetical population of extremely massive, luminous and hot stars with virtually no "metals", except possibly for intermixing ejecta from other nearby, early population III supernovae. The term was first introduced by Neville J. Woolf in 1965.^[25]^[26] Such stars are likely to have existed in the very early universe (i.e., at high redshift) and may have started the production of chemical elements heavier than hydrogen, which are needed for the later formation of planets and life as we know it.^[27]^[28]

The existence of population III stars is inferred from physical cosmology, but they have not yet been observed directly. Indirect evidence for their existence has been found in a gravitationally lensed galaxy in a very distant part of the universe.^[29] Their existence may account for the fact that heavy elements – which could not have been created in the Big Bang – are observed in quasar emission spectra.^[9] They are also thought to be components of faint blue galaxies. These stars likely triggered the universe's period of reionization, a major phase transition of the hydrogen gas composing most of the interstellar medium. Observations of the galaxy UDFy-38135539 suggest that it may have played a role in this reionization process. The European Southern Observatory discovered a bright pocket of early population stars in the very bright galaxy Cosmos Redshift 7 from the reionization period around 800 million years after the Big Bang, at $z = 6.60$ . The rest of the galaxy has some later redder population II stars.^[27]^[30] Some theories hold that there were two generations of population III stars.^[31]

Artist's impression of the first stars, 400 million years after the Big Bang

Current theory is divided on whether the first stars were very massive or not. One possibility is that these stars were much larger than current stars: several hundred solar masses, and possibly up to 1,000 solar masses. Such stars would be very short-lived and last only 2–5 million years.^[32] Such large stars may have been possible due to the lack of heavy elements and a much warmer interstellar medium from the Big Bang.^{[citation needed]} Conversely, theories proposed in 2009 and 2011 suggest that the first star groups might have consisted of a massive star surrounded by several smaller stars.^[33]^[34]^[35] The smaller stars, if they remained in the birth cluster, would accumulate more gas and could not survive to the present day, but a 2017 study concluded that if a star of 0.8 solar masses (M_☉) or less was ejected from its birth cluster before it accumulated more mass, it could survive to the present day, possibly even in our Milky Way galaxy.^[36]

Analysis of data of extremely low-metallicity population II stars such as HE 0107-5240, which are thought to contain the metals produced by population III stars, suggest that these metal-free stars had masses of 20~130 solar masses.^[37] On the other hand, analysis of globular clusters associated with elliptical galaxies suggests pair-instability supernovae, which are typically associated with very massive stars, were responsible for their metallic composition.^[38] This also explains why there have been no low-mass stars with zero metallicity observed, despite models constructed for smaller population III stars.^[39]^[40] Clusters containing zero-metallicity red dwarfs or brown dwarfs (possibly created by pair-instability supernovae^[16]) have been proposed as dark matter candidates,^[41]^[42] but searches for these types of MACHOs through gravitational microlensing have produced negative results.^{[citation needed]}

Population III stars are considered seeds of black holes in the early universe. Unlike high-mass black hole seeds, such as direct collapse black holes, they would have produced light ones. If they could have grown to larger than expected masses, then they could have been quasi-stars, other hypothetical seeds of heavy black holes which would have existed in the early development of the Universe before hydrogen and helium were contaminated by heavier elements.

Detection of population III stars is a goal of NASA's James Webb Space Telescope.^[43]

On 8 December 2022, astronomers reported the possible detection of Population III stars, in a high-redshift galaxy called RX J2129–z8He II.^[44]^[45]

Notes

^ It has been proposed that recent supernovae SN 2006gy and SN 2007bi may have been pair-instability supernovae where such super-massive population III stars exploded. Clark (2010) speculates that these stars could have formed relatively recently in dwarf galaxies, since they contain mainly primordial, metal-free interstellar matter. Past supernovae in these small galaxies could have ejected their metal-rich contents at speeds high enough for them to escape the galaxy, keeping the small galaxies' metal content very low.^[15]

References

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@@ Line 6: / Line 6: @@
 In the abstract of the article by Baade, he recognizes that [[Jan Oort]] originally conceived this type of classification in [[1926]].<ref name=Baade-1944/>
-Baade observed that bluer stars were strongly associated with the spiral arms, and yellow stars dominated near the central [[Spiral galaxy#Structure#Galactic bulge|galactic bulge]] and within [[globular cluster|globular star clusters]].<ref name=Shapley-1977/> Two main divisions were defined as '''[[Population I star|population&nbsp;I]]''' and '''population&nbsp;II''', with another newer, hypothetical division called '''population&nbsp;III''' added in 1978.
+Baade observed that bluer stars were strongly associated with the spiral arms, and yellow stars dominated near the central [[Spiral galaxy#Structure#Galactic bulge|galactic bulge]] and within [[globular cluster|globular star clusters]].<ref name=Shapley-1977/> Two main divisions were defined as '''Population I star''' and '''population&nbsp;II''', with another newer, hypothetical division called '''population&nbsp;III''' added in 1978.
 Among the population types, significant differences were found with their individual observed stellar spectra. These were later shown to be very important and were possibly related to star formation, observed [[kinematics]],<ref name=Gibson-etal-2013/> stellar age, and even [[Galaxy formation and evolution|galaxy evolution]] in both [[Spiral galaxy|spiral]] and [[Elliptical galaxy|elliptical]] galaxies. These three simple population classes usefully divided stars by their chemical composition or [[metallicity]].<ref name=Kunth-Östlin-2000/><ref name=schonrich2009/><ref name=Gibson-etal-2013/>
-By definition, each population group shows the trend where decreasing metal content indicates increasing age of stars. Hence, the first stars in the universe (very low metal content) were deemed population&nbsp;III, old stars (low metallicity) as population&nbsp;II, and recent stars (high metallicity) as population&nbsp;I.<ref name=Byant-2005/> The [[Sun]] is considered population&nbsp;I, a recent star with a relatively high 1.4% metallicity. Note that astrophysics nomenclature considers any element heavier than [[helium]] to be a "metal", including chemical [[non-metals]] such as oxygen.<ref name=metal/>
+By definition, each population group shows the trend where lower metal content indicates higher age of stars. Hence, the first stars in the universe (very low metal content) were deemed population&nbsp;III, old stars (low metallicity) as population&nbsp;II, and recent stars (high metallicity) as population&nbsp;I.<ref name=Byant-2005/> The [[Sun]] is considered population&nbsp;I, a recent star with a relatively high 1.4% metallicity. Note that astrophysics nomenclature considers any element heavier than [[helium]] to be a "metal", including chemical [[non-metals]] such as oxygen.<ref name=metal/>
 ==Stellar development==
@@ Line 28: / Line 28: @@
 As those population&nbsp;II stars died, they returned metal-enriched material to the [[interstellar medium]] via [[planetary nebula]]e and supernovae, enriching further the nebulae, out of which the newer stars formed. These youngest stars, including the [[Sun]], therefore have the highest metal content, and are known as population&nbsp;I stars.
-==Chemical classification by Baade==
+==Chemical classification by Walter Baade==
 ===Population I stars===
@@ Line 34: / Line 34: @@
 [[File:Treasures3.jpg|thumb|right|Population I star [[Rigel]] with [[reflection nebula]] [[IC&nbsp;2118]]]]
-Population&nbsp;I, or metal-rich, stars are young stars with the highest metallicity out of all three populations and are more commonly found in the [[spiral arm]]s of the [[Milky Way]] galaxy. The [[Sun]] is an example of a metal-rich star and is considered as an intermediate population&nbsp;I star, while the sun-like [[Mu Arae|{{mvar|μ}} Arae]] is much richer in metals.<ref name=Soriano-Vauclair-2009/>
+Population&nbsp;I stars are young stars with the highest metallicity out of all three populations and are more commonly found in the [[spiral arm]]s of the [[Milky Way]] galaxy. The [[Sun]] is considered as an intermediate population&nbsp;I star, while the sun-like [[Mu Arae|{{mvar|μ}} Arae]] is much richer in metals.<ref name=Soriano-Vauclair-2009/> (The term "metal rich star" is used to describe stars with a significantly higher metallicity than the Sun; higher than can be explained by measurement error.)
 Population&nbsp;I stars usually have regular [[elliptical orbit]]s of the [[Galactic Center]], with a low [[relative velocity]]. It was earlier hypothesized that the high metallicity of population&nbsp;I stars makes them more likely to possess [[planetary system]]s than the other two populations, because [[planet]]s, particularly [[terrestrial planet]]s, are thought to be formed by the [[accretion (astrophysics)|accretion]] of metals.<ref name=Lineweaver-2000/> However, observations of the [[Kepler Space Telescope]] data have found smaller planets around stars with a range of metallicities, while only larger, potential gas giant planets are concentrated around stars with relatively higher metallicity – a finding that has implications for theories of gas-giant formation.<ref name=Buchhave-etal-2012/> Between the intermediate population&nbsp;I and the population&nbsp;II stars comes the intermediate disc population.
@@ Line 41: / Line 41: @@
 {{anchor|Population II stars}}
-[[File:Milky way profile.svg|right|thumb|upright=1.2|Schematic profile of the Milky Way. Population&nbsp;II stars appear in the galactic bulge and within the globular clusters.]]
+[[File:Milky way profile.svg|right|thumb|upright=1.2|The Milky Way. Population&nbsp;II stars are in the galactic bulge and globular clusters.]]
-[[File:Massive,_Population_III_Star_in_the_Early_Universe.jpg|right|thumb|upright=1.2|This artist’s impression shows a field of population&nbsp;III stars as they would have appeared a mere 100&nbsp;million years after the [[Big Bang]].]]
+[[File:Massive,_Population_III_Star_in_the_Early_Universe.jpg|right|thumb|upright=1.2|Artist’s impression of a field of population&nbsp;III stars 100&nbsp;million years after the [[Big Bang]].]]
 Population&nbsp;II, or metal-poor, stars are those with relatively little of the elements heavier than helium. These objects were formed during an earlier time of the universe. Intermediate population&nbsp;II stars are common in the [[bulge (astronomy)|bulge]] near the centre of the [[Milky Way]], whereas population&nbsp;II stars found in the [[Galactic spheroid#Galactic spheroid|galactic halo]] are older and thus more metal-deficient. [[Globular clusters]] also contain high numbers of population&nbsp;II stars.<ref name=va1973/>
@@ Line 54: / Line 54: @@
 [[File:Ssc2005-22a1.jpg|thumb|right|upright=1.4|Possible glow of population&nbsp;III stars imaged by [[NASA]]'s [[Spitzer Space Telescope]]]]
-Population&nbsp;III stars<ref name=Tominga-etal-2007/> are a hypothetical population of extremely massive, luminous and hot stars with virtually no [[metallicity|"metals"]], except possibly for intermixing ejecta from other nearby, early population&nbsp;III supernovae. The term was first introduced by Neville J. Woolf in 1965.<ref>{{cite journal |last1=Green |first1=Louis |title=Observational Aspects of Cosmology |journal=Sky and Telescope |date=April 1966 |volume=31 |page=199 |bibcode=1966S&T....31..199G |url=https://ui.adsabs.harvard.edu/abs/1966S%26T....31..199G/abstract}}</ref><ref>{{cite journal |last1=Thornton |first1=Page |title=Observational Aspects of Cosmology |journal=Science |date=March 1966 |volume=151 |issue=3716 |pages=1411-1414,1416-1418 |bibcode=1966Sci...151.1411P |url=https://ui.adsabs.harvard.edu/abs/1966Sci...151.1411P/abstract}}</ref> Such stars are likely to have existed in the very early universe (i.e., at high redshift) and may have started the production of [[chemical element]]s heavier than [[hydrogen]], which are needed for the later formation of [[planet]]s and [[life]] as we know it.<ref name=Sobral-etal-2015-06/><ref name=NYT-2015-06-17/>
+Population&nbsp;III stars<ref name=Tominga-etal-2007/> are a hypothetical population of extremely massive, luminous and hot stars with virtually no [[metallicity|"metals"]], except possibly for intermixing ejecta from other nearby, early population&nbsp;III supernovae. The term was first introduced by Neville J. Woolf in 1965.<ref>{{cite journal |last1=Green |first1=Louis |title=Observational Aspects of Cosmology |journal=Sky and Telescope |date=April 1966 |volume=31 |page=199 |bibcode=1966S&T....31..199G |url=https://ui.adsabs.harvard.edu/abs/1966S%26T....31..199G/abstract}}</ref><ref>{{cite journal |last1=Thornton |first1=Page |title=Observational Aspects of Cosmology |journal=Science |date=March 1966 |volume=151 |issue=3716 |pages=1411-1414,1416-1418 |doi=10.1126/science.151.3716.1411 |pmid=17817304 |bibcode=1966Sci...151.1411P |url=https://ui.adsabs.harvard.edu/abs/1966Sci...151.1411P/abstract}}</ref> Such stars are likely to have existed in the very early universe (i.e., at high redshift) and may have started the production of [[chemical element]]s heavier than [[hydrogen]], which are needed for the later formation of [[planet]]s and [[life]] as we know it.<ref name=Sobral-etal-2015-06/><ref name=NYT-2015-06-17/>
 The existence of population&nbsp;III stars is inferred from [[physical cosmology]], but they have not yet been observed directly. Indirect evidence for their existence has been found in a [[gravitationally lensed galaxy]] in a very distant part of the universe.<ref name=Fosbury-etal-2003/> Their existence may account for the fact that heavy elements – which could not have been created in the [[Big Bang]] – are observed in [[quasar]] [[emission spectrum|emission spectra]].<ref name=Heger-Woosley-2002/> They are also thought to be components of [[faint blue galaxy|faint blue galaxies]]. These stars likely triggered the universe's period of [[reionization]], a major [[phase transition]] of the hydrogen gas composing most of the interstellar medium. Observations of the galaxy [[UDFy-38135539]] suggest that it may have played a role in this reionization process. The [[European Southern Observatory]] discovered a bright pocket of early population stars in the very bright galaxy [[Cosmos Redshift&nbsp;7]] from the reionization period around 800&nbsp;million years after the Big Bang, at {{math|''z'' {{=}} 6.60}}. The rest of the galaxy has some later redder population&nbsp;II stars.<ref name=Sobral-etal-2015-06/><ref name=Astronomy-2017-06-17-ESO/> Some theories hold that there were two generations of population&nbsp;III stars.<ref name=Bromm/>
@@ Line 61: / Line 61: @@
 Current theory is divided on whether the first stars were very massive or not. One possibility is that these stars were much larger than current stars: several hundred [[solar mass]]es, and possibly up to 1,000&nbsp;solar masses. Such stars would be very short-lived and last only 2–5&nbsp;million years.<ref name=Ohkubo-etal-2009/> Such large stars may have been possible due to the lack of heavy elements and a much warmer [[interstellar medium]] from the Big Bang.{{Citation needed|date=June 2017}} Conversely, theories proposed in 2009 and 2011 suggest that the first star groups might have consisted of a massive star surrounded by several smaller stars.<ref name=Space_FS/><ref name=Space_MS/><ref name=Carr-essay/> The smaller stars, if they remained in the birth cluster, would accumulate more gas and could not survive to the present day, but a 2017 study concluded that if a star of 0.8&nbsp;solar masses ({{solar mass}}) or less was ejected from its birth cluster before it accumulated more mass, it could survive to the present day, possibly even in our Milky Way galaxy.<ref name=Dutta-etal-2017/>
-Analysis of data of extremely low-[[metallicity]] population&nbsp;II stars such as [[HE&nbsp;0107-5240]], which are thought to contain the metals produced by population&nbsp;III stars, suggest that these metal-free stars had masses of 20~130&nbsp;solar masses.<ref name=Umeda-Nomoto-2003/> On the other hand, analysis of [[globular cluster]]s associated with [[elliptical galaxies]] suggests [[pair-instability supernova]]e, which are typically associated with very massive stars, were responsible for their [[metallicity|metallic]] composition.<ref name=Puzia-etal-2006/> This also explains why there have been no low-mass stars with zero [[metallicity]] observed, although models have been constructed for smaller population&nbsp;III stars.<ref name=Siess-Livio-Lattanzio-2002/><ref name=gibson2012/> Clusters containing zero-metallicity [[red dwarfs]] or [[brown dwarfs]] (possibly created by pair-instability supernovae<ref name=Salvaterra-Ferrara-Schneider-2004/>) have been proposed as [[dark matter]] candidates,<ref name=Kerins-1997/><ref name=Sanchez-1997/> but searches for these types of [[Massive compact halo object|MACHO]]s through [[gravitational microlensing]] have produced negative results.{{Citation needed|date=February 2019}}
+Analysis of data of extremely low-[[metallicity]] population&nbsp;II stars such as [[HE&nbsp;0107-5240]], which are thought to contain the metals produced by population&nbsp;III stars, suggest that these metal-free stars had masses of 20~130&nbsp;solar masses.<ref name=Umeda-Nomoto-2003/> On the other hand, analysis of [[globular cluster]]s associated with [[elliptical galaxies]] suggests [[pair-instability supernova]]e, which are typically associated with very massive stars, were responsible for their [[metallicity|metallic]] composition.<ref name=Puzia-etal-2006/> This also explains why there have been no low-mass stars with zero [[metallicity]] observed, despite models constructed for smaller population&nbsp;III stars.<ref name=Siess-Livio-Lattanzio-2002/><ref name=gibson2012/> Clusters containing zero-metallicity [[red dwarfs]] or [[brown dwarfs]] (possibly created by pair-instability supernovae<ref name=Salvaterra-Ferrara-Schneider-2004/>) have been proposed as [[dark matter]] candidates,<ref name=Kerins-1997/><ref name=Sanchez-1997/> but searches for these types of [[Massive compact halo object|MACHO]]s through [[gravitational microlensing]] have produced negative results.{{Citation needed|date=February 2019}}
-Population&nbsp;II stars are considered seeds of black holes in the early universe but unlike high-mass [[black hole]] seeds like [[Direct collapse black hole|direct collapse black holes]] they would have produced light ones, if they could have grown to larger than expected masses then they could have been [[Quasi-star|quasi-stars]], other hypothetical seeds of heavy black holes which would have existed in the early development of the Universe before hydrogen and helium were contaminated by heavier elements.
+Population&nbsp;III stars are considered seeds of black holes in the early universe. Unlike high-mass [[black hole]] seeds, such as [[Direct collapse black hole|direct collapse black holes]], they would have produced light ones. If they could have grown to larger than expected masses, then they could have been [[Quasi-star|quasi-stars]], other hypothetical seeds of heavy black holes which would have existed in the early development of the Universe before hydrogen and helium were contaminated by heavier elements.
-Detection of population&nbsp;III stars is a goal of NASA's [[James Webb Space Telescope]].<ref name=JW_PIII/> New [[Spectroscopy|spectroscopic]] surveys, such as [[SEGUE]] or [[Sloan Digital Sky Survey#SDSS-II|SDSS-II]], may also locate population&nbsp;III stars.{{citation needed|date=January 2015}}
+Detection of population&nbsp;III stars is a goal of NASA's [[James Webb Space Telescope]].<ref name=JW_PIII/>
-On 8 December 2022, astronomers reported the possible detection of Population III stars.<ref name="ARX-20221208">{{cite arXiv |author=Wang, Xin |display-authors=et al. |title=A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars? |date=8 December 2022 |class=astro-ph.GA |eprint=2212.04476 }}</ref><ref name="QUANT-20230130">{{cite news |last=Callaghan |first=Jonathan |title=Astronomers Say They Have Spotted the Universe's First Stars - Theory has it that "Population III" stars brought light to the cosmos. The James Webb Space Telescope may have just glimpsed them. |url=https://www.quantamagazine.org/astronomers-say-they-have-spotted-the-universes-first-stars-20230130/ |date=30 January 2023 |work=[[Quanta Magazine]] |accessdate=31 January 2023 }}</ref>
+On 8 December 2022, astronomers reported the possible detection of Population III stars, in a high-[[redshift]] galaxy called RX J2129–z8He II.<ref name="ARX-20221208">{{cite arXiv |author=Wang, Xin |display-authors=et al. |title=A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars? |date=8 December 2022 |class=astro-ph.GA |eprint=2212.04476 }}</ref><ref name="QUANT-20230130">{{cite news |last=Callaghan |first=Jonathan |title=Astronomers Say They Have Spotted the Universe's First Stars - Theory has it that "Population III" stars brought light to the cosmos. The James Webb Space Telescope may have just glimpsed them. |url=https://www.quantamagazine.org/astronomers-say-they-have-spotted-the-universes-first-stars-20230130/ |date=30 January 2023 |work=[[Quanta Magazine]] |accessdate=31 January 2023 }}</ref>
 == See also ==
@@ Line 119: / Line 119: @@
 </ref>
-<ref name=Byant-2005>
+<ref name=Byant-2005>{{cite web
+ |first=Lauren J.
-{{cite web
- |first=Lauren J. |last=Bryant
+ |last=Bryant
  |title=What makes stars tick
  |series=Research & Creative Activity
- |volume=27  |issue=1
+ |volume=27
+ |issue=1
  |publisher=[[Indiana University]]
  |url=http://www.indiana.edu/~rcapub/v27n1/tick.shtml
  |access-date=September 7, 2005
+ |archive-date=May 16, 2016
-}}
+ |archive-url=https://web.archive.org/web/20160516085737/http://www.indiana.edu/~rcapub/v27n1/tick.shtml
-</ref>
+ |url-status=dead
+ }}</ref>
 <ref name=Buchhave-etal-2012>
@@ Line 193: / Line 196: @@
 </ref>
-<ref name=Gibson-etal-2013>
+<ref name=Gibson-etal-2013>{{cite journal
+ |first1       = B.K.
-{{cite journal
- |first1=B.K. |last1=Gibson
+ |last1        = Gibson
- |first2=Y.   |last2=Fenner
+ |first2       = Y.
- |first3=A.   |last3=Renda
+ |last2        = Fenner
- |first4=D.   |last4=Kawata
+ |first3       = A.
+ |last3        = Renda
- |first5=L.   |last5=Hyun-chul
+ |first4       = D.
- |year=2013
+ |last4        = Kawata
- |title=Review: Galactic chemical evolution
+ |first5       = L.
- |journal=Publications of the Astronomical Society of Australia
+ |last5        = Hyun-chul
- |volume=20  |issue=4  |pages=401–415
+ |year         = 2013
- |publisher=CSIRO publishing
+ |title        = Review: Galactic chemical evolution
- |doi=10.1071/AS03052  |bibcode=2003PASA...20..401G
+ |journal      = Publications of the Astronomical Society of Australia
- |arxiv=astro-ph/0312255
+ |volume       = 20
- |s2cid=12253299
+ |issue        = 4
- |url=http://astro.wsu.edu/hclee/pasa_review_GCE.pdf
+ |pages        = 401–415
- |access-date=17 April 2018
+ |publisher    = CSIRO publishing
-}}
+ |doi          = 10.1071/AS03052
-</ref>
+ |bibcode      = 2003PASA...20..401G
+ |arxiv        = astro-ph/0312255
+ |s2cid        = 12253299
+ |url          = http://astro.wsu.edu/hclee/pasa_review_GCE.pdf
+ |access-date  = 17 April 2018
+ |archive-date = 20 January 2021
+ |archive-url  = https://web.archive.org/web/20210120224726/http://astro.wsu.edu/hclee/pasa_review_GCE.pdf
+ |url-status   = dead
+}}</ref>
 <ref name=Heger-Woosley-2002>
@@ Line 238: / Line 250: @@
  |volume=429  |issue=4  |pages=3658–3664
  | bibcode=2013MNRAS.429.3658R |doi=10.1093/mnras/sts653
+ |doi-access=free
  |arxiv=1206.0007
 }}
@@ Line 312: / Line 325: @@
 {{cite journal
  |last1=Puzia          |first1=Thomas H.
- |last2=Kissler‐Patig  |first2=Markus
+ |last2=Kissler-Patig  |first2=Markus
  |last3=Goudfrooij     |first3=Paul
  |year=2006
- |title=Extremely α‐enriched globular clusters in early‐type galaxies: A step toward the dawn of stellar populations?
+ |title=Extremely α-enriched globular clusters in early-type galaxies: A step toward the dawn of stellar populations?
  |journal=[[The Astrophysical Journal]]
  |volume=648  |issue=1  |pages=383–388
@@ Line 591: / Line 604: @@
 ==Further reading==
 * {{cite journal
- |last1=Gibson |first1=B.&nbsp;K.
+ |last1=Gibson
+ |first1=B.&nbsp;K.
  |display-authors=etal
  |title=Review: Galactic Chemical Evolution
@@ Line 598: / Line 612: @@
  |url=http://astro.wsu.edu/hclee/pasa_review_GCE.pdf
  |access-date=17 April 2018
+ |archive-date=20 January 2021
-}}
+ |archive-url=https://web.archive.org/web/20210120224726/http://astro.wsu.edu/hclee/pasa_review_GCE.pdf
+ |url-status=dead
+ }}
 * {{cite book
  |last=Ferris  |first=Timothy
@@ Line 619: / Line 636: @@
 {{Star}}
 {{Portal bar|Astronomy|Spaceflight|Outer space|Solar System|Science}}
+[[Category:Physical cosmological concepts]]
 [[Category:Stellar astronomy|Population]]