Stellar populations ( English stellar populations ) - types of stellar composition of galaxies . They differ in chemical composition, spatial distribution, position on the Hertzsprung-Russell diagram , intrinsic velocities and other criteria. Classification by two populations was proposed by Baade in 1944 [1] and supplemented by another group in the late 1970s [2] [3] [4] .
Content
The division of the population of galaxies into types is rather arbitrary. Each population consists of several subtypes that have their own characteristics. There is also no consensus on the existence of stellar population III; some researchers believe that the first stars in the Universe belong to a special subcategory of population II.
Classification
Population I is characterized by a noticeable content in the spectrum of elements heavier than helium (astronomers call them "metals"). Heavy elements formed in earlier stars and spread through supernova explosions . The sun , like most stars in the galactic disk, is a typical representative of population I.
In the stars of population II, the content of heavy elements is several orders of magnitude lower. These are old stars that formed shortly after the Big Bang , older than 10 billion years. In spiral galaxies, population II consists of globular clusters in the galactic halo .
The hypothetical population III should be the first generation of stars after the Big Bang [5] . It is assumed that these are very heavy stars with a short lifetime, which did not survive to this day. The large mass is due to the lack of carbon necessary for the catalytic CNO cycle of hydrogen combustion - in such stars only the proton-proton thermonuclear cycle could occur, requiring high temperatures. There are several works of the 2010s describing galaxies, probably consisting of such stars [6] .
The stars of population III, as very massive, evolved very quickly, and their life expectancy was about a million years. For this reason, they are currently not visible in our Galaxy. The oldest known star is SMSS J031300.36-670839.3 , which was made from material from a single supernova explosion. Probably, this star was created in the transition period between the age of the population of the III star and the population of II.
Planned new far infrared space missions, such as the James Webb Space Telescope , are designed to help explain the nature of the stars of the third population.
See also
- Metallicity
Notes
- ↑ W. Baade. The Resolution of Messier 32, NGC 205, and the Central Region of the Andromeda Nebula. (Eng.) // The Astrophysical Journal : journal. - IOP Publishing , 1944. - Vol. 100 . - P. 121-146 . - DOI : 10.1086 / 144650 . - .
- ↑ MJ Rees. Origin of pregalactic microwave background (Eng.) // Nature. - 1978. - Vol. 275 . - P. 35-37 . - DOI : 10.1038 / 275035a0 . - .
- ↑ SDM White; MJ Rees. Core condensation in heavy halos - A two-stage theory for galaxy formation and clustering (Eng.) // Monthly Notices Royal Astronomical Society: journal. - 1978. - Vol. 183 . - P. 341-358 . - DOI : 10.1093 / mnras / 183.3.341 . - .
- ↑ JL Puget; J. Heyvaerts. Population III stars and the shape of the cosmological black body radiation (Eng.) // Astronomy and Astrophysics : journal. - 1980. - Vol. 83 . - P. L10 — L12 . - .
- ↑ Bromm, Volker; Larson, Richard B. THE FIRST STARS (Eng.) // Annual Review of Astronomy and Astrophysics : journal. - 2004. - Vol. 42 . - P. 79-118 . - DOI : 10.1146 / annurev.astro.42.053102.134034 . - . - arXiv : astro-ph / 0311019 .
- ↑ "Evidence for PopIII-like stellar populations in the most luminous Lyman-α emitters at the epoch of re-ionization: spectroscopic confirmation", D. Sobral, et al. // The Astrophysical Journal. 2015, Arxiv: 1504.01734 preprint
The brightest distant galaxy CR7 with population stars III was discovered with the VLT telescope on June 17, 2015.
Literature
- Rosemary FG Wyse, Stellar Populations / Planets, Stars and Stellar Systems 2013, pp 1-19 doi: 10.1007 / 978-94-007-5612-0_1 ISBN 978-94-007-5611-3
Links
- Stars - Stellar Populations // Astronomy Online