# Stellar age estimation

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Methods for estimating the age of a star

Young star ejecting two jets of energised gas[1]

Various methods and tools are involved in **stellar age estimation**, an attempt to identify within reasonable degrees of confidence what the age of a star is. These methods include stellar [evolutionary models](/source/Stellar_evolution), membership in a given [star cluster](/source/Star_cluster) or [system](/source/Star_system), fitting the star with the standard [spectral and luminosity classification system](/source/Stellar_classification), and the presence of a [protoplanetary disk](/source/Protoplanetary_disk), among others. Nearly all of the methods of determining age require knowledge of the mass of the star, which can be known through various methods. No individual method can provide accurate results for all types of stars.[2]

## Luminosity increase and the Hertzsprung–Russell diagram

As stars grow older, their luminosity increases at an appreciable rate.[3] Given the mass of the star, one can use this rate of increase in luminosity in order to determine the age of the star. This method only works for calculating stellar age on the [main sequence](/source/Main_sequence), because in advanced evolutionary stages of the star, such as the [red giant](/source/Red_giant) stage, the standard relationship for the determination of age no longer holds. However, when one can observe a red giant star with a known mass, one can calculate the main-sequence lifetime,[4] and thus the minimum age of star is known given that it is in an advanced stage of its evolution. As the star spends only about 1% of its total lifetime as a red giant,[5] this is an accurate method of determining age.

## Field stars

[Eta Carinae](/source/Eta_Carinae), a star system that is violently ejecting gas

Various properties of stars can also be used to determine their age. For example, the [Eta Carinae](/source/Eta_Carinae) system is emitting large quantities of gas and dust. These enormous outbursts can be used to infer that the star system is nearing the end of its life, and will explode as a [supernova](/source/Supernova) within a relatively short period of astronomical time.[6] Very large stars like [VY Canis Majoris](/source/VY_Canis_Majoris), one of the [largest stars known](/source/List_of_largest_known_stars), together with [NML Cygni](/source/NML_Cygni), [VX Sagittarii](/source/VX_Sagittarii) and [Trumpler 27-1](/source/Trumpler_27-1) all have radii larger than that of the average orbital radius of [Jupiter](/source/Jupiter) in the [Solar System](/source/Solar_System), thus showing that they are in extremely late evolutionary stages.[7] [Betelgeuse](/source/Betelgeuse) in particular is expected to die in a supernova explosion within the next million years.[8]

As well as the scenarios of supermassive stars violently casting off their outer layers before their deaths, other examples can be found of the properties of stars which illustrate their age. For example, [Cepheid variables](/source/Cepheid_variables) have a characteristic pattern in their [lightcurves](/source/Lightcurve), the rate of repetition of which is dependent on the luminosity of the star.[9] Since Cepheid variables are a relatively short evolutionary stage in the lifecycle of stars, and knowing the mass of the star allows for the star to be tracked in its evolutionary path, one can estimate the age of the Cepheid variable.

Exceptional stellar properties which allow for an estimation of age are not confined to advanced evolutionary stages. When a roughly solar-mass star exhibits [T Tauri variability](/source/T_Tauri_star), astronomers can locate the age of the star as being before the beginning of the [main sequence](/source/Main_sequence) phase of the star's life.[10] Additionally, more massive pre-main-sequence stars could be [Herbig Ae/Be stars](/source/Herbig_Ae%2FBe_star).[11] If a [red dwarf](/source/Red_dwarf) star is emitting immense [stellar flares](/source/Stellar_flare) and [x-rays](/source/X-rays), the star can be calculated to be in an early stage of its main-sequence lifetime, after which it will become less variable and become stable.[12]

## Membership in a star cluster or system

[47 Tucanae](/source/47_Tucanae), a [globular cluster](/source/Globular_cluster)

Membership in a [star cluster](/source/Star_cluster) or [star system](/source/Star_system) permits an assignment of rough ages to a large number of stars present within. When one can determine the age of stars through other methods, such as the ones listed above, one can identify the age of all of the bodies in a system.[13] This is especially useful in clusters of stars which exhibit a large amount of variety in their stellar masses, evolutionary stages, and classifications. While not *entirely* independent of the properties of the stars in the cluster, system, or other reasonably-sized association of stars, an astronomer would only need a representative sample of stars to determine the age of the cluster, rather than painstakingly finding the age of every star in the cluster through other properties.

In addition, knowing the age of one member of a star system can help determine the age of that system. In a star system, stars almost always form at the same time as each other, and given the age of one star, the age of all of the others can be known.[14]

However, this method does not work for [galaxies](/source/Galaxies). These units are much larger, and are not merely a one-off creation of stars which allows their age to be determined in this fashion. The creation of stars in a galaxy takes place over billions of years,[15] even though star production may long since have ceased (see [elliptical galaxy](/source/Elliptical_galaxy)). The oldest stars in a galaxy can only set a minimum age for the galaxy (when star formation began) but by no means determine the actual age.[16]

## Presence of a protoplanetary disk

See also: [Protoplanetary disk](/source/Protoplanetary_disk)

Along with other factors, the presence of a [protoplanetary disk](/source/Protoplanetary_disk) sets a maximum limit on the age of stars. Stars with protoplanetary disks are typically young, having moved onto the main sequence only a relatively short time ago.[17] Over time, this disk would coalesce to form [planets](/source/Planets), with leftover material being deposited into various [asteroid belts](/source/Asteroid_belt) and other similar locations. However, the presence of [pulsar planets](/source/Pulsar_planet) complicates this method as a determinant of age.

## Gyrochronology

Main article: [Gyrochronology](/source/Gyrochronology)

Gyro-chronology is a method used to determine the age of [field stars](https://en.wikipedia.org/w/index.php?title=Field_stars&action=edit&redlink=1) by measuring their rotation rate, and then comparing this rate with the rotation rate of the Sun, which serves as a precalibrated clock for this measurement.[18] This method has been seen as a more accurate method for the determination of stellar ages than other methods for field stars.[18]

## See also

- [Gyrochronology](/source/Gyrochronology)

- [Stellar evolution](/source/Stellar_evolution)

## References

1. **[^](#cite_ref-1)** ["A cosmic lightsabre"](http://www.spacetelescope.org/images/heic1526a/). Retrieved 21 December 2015.

1. **[^](#cite_ref-astroreview_2-0)** Soderblom, David R. (2010). "The Ages of Stars". *Annual Review of Astronomy and Astrophysics*. **48**: 581–629. [arXiv](/source/ArXiv_(identifier)):[1003.6074](https://arxiv.org/abs/1003.6074). [Bibcode](/source/Bibcode_(identifier)):[2010ARA&A..48..581S](https://ui.adsabs.harvard.edu/abs/2010ARA&A..48..581S). [doi](/source/Doi_(identifier)):[10.1146/annurev-astro-081309-130806](https://doi.org/10.1146%2Fannurev-astro-081309-130806). [S2CID](/source/S2CID_(identifier)) [119102781](https://api.semanticscholar.org/CorpusID:119102781).

1. **[^](#cite_ref-theuniverse-2011_3-0)** [Brownlee, Donald](/source/Donald_Brownlee) (29 November 2011). ["Worst Days on Planet Earth"](https://www.history.com/shows/the-universe/season-6/episode-5). [*The Universe*](/source/The_Universe_(TV_series)). Season 6. Episode 5. Event occurs at 41:46. History. Retrieved 15 July 2018. The sun gets brighter about 10% every billion years.

1. **[^](#cite_ref-swin-main-seq_4-0)** ["Main Sequence Lifetime"](http://astronomy.swin.edu.au/cosmos/M/Main+Sequence+Lifetime). *Swinburne Astronomy Online*. [Swinburne University of Technology](/source/Swinburne_University_of_Technology). Retrieved 7 March 2012.

1. **[^](#cite_ref-swin-red-giant_5-0)** ["Red giant stars"](http://astronomy.swin.edu.au/cosmos/R/Red+giant+stars). *Swinburne Astronomy Online*. Swinburne University of Technology. Retrieved 7 March 2012.

1. **[^](#cite_ref-apod-2006_6-0)** Nemiroff, R.; Bonnell, J., eds. (26 March 2006). ["Doomed Star Eta Carinae"](https://apod.nasa.gov/apod/ap060326.html). *[Astronomy Picture of the Day](/source/Astronomy_Picture_of_the_Day)*. [NASA](/source/NASA). Retrieved 7 March 2012.

1. **[^](#cite_ref-vy-cm_7-0)** Cain, Fraser. ["VY Canis Majoris"](http://www.universetoday.com/65650/vy-canis-majoris/). [Universe Today](/source/Universe_Today). Retrieved 7 March 2012.

1. **[^](#cite_ref-oneill-betelgeuse_8-0)** Ian, O'Neill. ["DON'T PANIC: Betelgeuse Won't Explode in 2012"](http://news.discovery.com/space/dont-panic-betelgeuse-wont-explode-in-2012.html). Discovery News. Retrieved 7 March 2012.

1. **[^](#cite_ref-soper-cepheid_9-0)** Soper, Davidson E. ["Cepheid Variable Stars"](http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html). *ASTR 123*. Retrieved 7 March 2012.

1. **[^](#cite_ref-cain-622009_10-0)** Cain, Fraser (6 February 2009). ["T Tauri Star"](http://www.universetoday.com/24802/t-tauri-star/). Universe Today. Retrieved 7 March 2012.

1. **[^](#cite_ref-11)** [Herbig Ae/Be stars](https://web.archive.org/web/20060917092653/http://astro.berkeley.edu/ay216/NOTES/Lecture27.pdf)

1. **[^](#cite_ref-schirber-2009_12-0)** Schirber, Michael (9 April 2009). ["Can Life Thrive Around a Red Dwarf Star?"](http://www.space.com/6560-life-thrive-red-dwarf-star.html). [Space.com](/source/Space.com).

1. **[^](#cite_ref-jiminez-1998_13-0)** Jiminez, Raul (6 January 1998). ["Globular cluster ages"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC34183). *Proceedings of the National Academy of Sciences*. **95** (1): 13–17. [Bibcode](/source/Bibcode_(identifier)):[1998PNAS...95...13J](https://ui.adsabs.harvard.edu/abs/1998PNAS...95...13J). [doi](/source/Doi_(identifier)):[10.1073/pnas.95.1.13](https://doi.org/10.1073%2Fpnas.95.1.13). [PMC](/source/PMC_(identifier)) [34183](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC34183). [PMID](/source/PMID_(identifier)) [9419317](https://pubmed.ncbi.nlm.nih.gov/9419317).

1. **[^](#cite_ref-astro-161_14-0)** ["Binary Star Systems Versus Planetary System"](http://csep10.phys.utk.edu/astr161/lect/solarsys/binary.html). *Astronomy 161 lectures*. Retrieved 7 March 2012.

1. **[^](#cite_ref-utoday-08_15-0)** Wethington, Nicholos. ["Age of the Milky Way"](http://www.universetoday.com/21822/age-of-the-milky-way/). *Universe Today*. Retrieved 7 March 2012.

1. **[^](#cite_ref-wethington-2008-2_16-0)** Wethington, Nicholos. ["Facts about the Milky Way"](http://www.universetoday.com/22285/facts-about-the-milky-way/). *Universe Today*. Retrieved 7 March 2012.

1. **[^](#cite_ref-17)** Mamajek, E.E.; Usuda, Tomonori; Tamura, Motohide; Ishii, Miki (2009). "Initial Conditions of Planet Formation: Lifetimes of Primordial Disks". *AIP Conference Proceedings*. **1158**: 3–10. [arXiv](/source/ArXiv_(identifier)):[0906.5011](https://arxiv.org/abs/0906.5011). [Bibcode](/source/Bibcode_(identifier)):[2009AIPC.1158....3M](https://ui.adsabs.harvard.edu/abs/2009AIPC.1158....3M). [doi](/source/Doi_(identifier)):[10.1063/1.3215910](https://doi.org/10.1063%2F1.3215910). [S2CID](/source/S2CID_(identifier)) [16660243](https://api.semanticscholar.org/CorpusID:16660243).

1. ^ [***a***](#cite_ref-astrobio_18-0) [***b***](#cite_ref-astrobio_18-1) ["Gyrochronology"](https://web.archive.org/web/20101104023758/http://www.astrobio.net/pressrelease/2315/gyrochronology). *Astrobiology Magazine*. Archived from [the original](http://www.astrobio.net/pressrelease/2315/gyrochronology) on 4 November 2010. Retrieved March 18, 2012.

## External links

- [Red Dwarf Stars from UniverseToday](http://www.universetoday.com/24670/red-dwarf-stars/)

- [What is a Binary Star? from UniverseToday](http://www.universetoday.com/24203/what-is-a-binary-star/)

- [Review Article:Protoplanetary Disks and their Evolution from Astrobites](http://astrobites.com/2011/03/11/review-article-protoplanetary-disks-and-their-evolution/)

v t e Stars List Formation Accretion Molecular cloud Bok globule Young stellar object Protostar Pre-main-sequence Herbig Ae/Be T Tauri Herbig–Haro object Hayashi track Henyey track Evolution Main sequence Red-giant branch Horizontal branch Red clump Asymptotic giant branch post-AGB super-AGB Blue loop Planetary nebula Protoplanetary Wolf–Rayet nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Stellar population Supernova Superluminous Hypernova Classification Early Late Main sequence O B A F G K M Subdwarf O B WR OB Subgiant Hertzsprung gap Giant Blue Red Yellow Bright giant Supergiant Blue Red Yellow Hypergiant Yellow Carbon S CN CH White dwarf Chemically peculiar Am Ap/Bp CEMP HgMn He-weak Barium Lambda Boötis Lead Technetium Be Shell B[e] Helium Extreme Blue straggler Remnants Compact star White dwarf Helium planet Neutron Radio-quiet Pulsar Binary X-ray Magnetar Black hole Stellar black hole Supermassive black hole X-ray binary Burster SGR Hypothetical Blue dwarf Black dwarf Exotic Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Quasi-star Gravastar Thorne–Żytkow object Iron Blitzar White hole Nucleosynthesis Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process C burning Ne burning O burning Si burning s-process r-process p-process Nova Symbiotic Remnant Luminous red nova Recurrent Micronova Supernova Structure Core Convection zone Microturbulence Oscillations Radiation zone Atmosphere Photosphere Starspot Chromosphere Stellar corona Alfvén surface Stellar wind Bubble Bipolar outflow Accretion disk Protoplanetary disk Proplyd Asteroseismology Helioseismology Circumstellar dust Cosmic dust Circumstellar envelope Eddington luminosity Kelvin–Helmholtz mechanism Properties Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Loss Metallicity Rotation Gravity darkening Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram Strömgren sphere Kraft break Star systems Binary Contact Common envelope Eclipsing Symbiotic Multiple Cluster Open Globular Super Planetary system Earth-centric observations Sun Solar eclipse Solar radio emission Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard Lists Proper names Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest Historical brightest Most luminous Nearest bright Most distant With resolved images With multiple exoplanets Brown dwarfs Red dwarfs White dwarfs Milky Way novae Supernovae Candidates Remnants Planetary nebulae Timeline of stellar astronomy Related Substellar object Brown dwarf Desert Sub Planet Galactic year Galaxy Guest Gravity Intergalactic Neutron star merger Planet-hosting stars Stellar collision Stellar engulfment Tidal disruption event Category Stars portal

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Adapted from the Wikipedia article [Stellar age estimation](https://en.wikipedia.org/wiki/Stellar_age_estimation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Stellar_age_estimation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.