Years of formation of universe, early stars, galaxies and quasars
Formation of Universe:
Universe is thought to be formed about 13.8 ± 0.2 billion years ago at the Hubble constant H0 = 67.3 ± 1.2 km/s/Mpc, and a high value of the matter density parameter, Ωm = 0.315±0.017.
Formation of metals:
Scientists are of the opinion that only elements up to 4He and traces of Li, Be, B were formed in the early universe during Big Bang Nucleosynthesis (BBN), while heavier elements were formed by stellar nucleosynthesis and dispersed in the interstellar space by the supernova explosions.
Researchers are of the opinion that probably star formation started earlier than the formation of quasars. Those early stars produced supernovae and gave the metals to the space around them.
Astronomers are of the opinion that although the star formation started much earlier, i.e. redshift of about 30 (z∼30) but huge number of stars and galaxies have been formed very recently showing the redshifts of the order unity zform ≤ 10. Some stars are as old as the age of the universe (or older than the age of the universe) and some of the examples of those stars are present in our Milky Way. Some examples of those stars are presented below:
- A star in the galactic halo, HE 1523-0901, is about 13.2 billion years old
- The age of BD+17o 3248 is estimated to be 13.8 ± 4 billion years
- The age of the star HD 140 283 is 14.46 ± 0.31 billion years
Researchers are of the opinion that the age of these stars (whose value is exceeding the age of the universe) could be pregalactic stars that were captured by the galaxy later and they behaved as cold dark matter.
Galaxies and clusters of galaxies are thought to be formed at z = 2 − 3, i.e. about 3.27-2.14 billion years after the formation of universe. However, some of the galaxies are thought to be formed at high redshifts as there is an example of a galaxy, i.e. cluster MACS J1149+2223, at the redshift z ∼ 9.6 corresponding to the age of about 500 million years after the formation of universe and there is another example of a galaxy at redshift z ∼ 11 corresponding to the universe age of 410 million years.
Quasars are compact objects in space, usually with a large red shift indicating extreme remoteness, that emit huge amounts of energy, sometimes equal to the energy output of an entire galaxy. They are also supposed to be supermassive blackholes.
They are also among the early formed objects in the universe. The maximum redshift of an observed quasar is 7.085 corresponding to the age of about 750 million years after universe formation.
It has been found that about 30% of all baryons – a subatomic particle belonging to a group that undergo strong interactions, have a mass greater than or equal to that of the proton, and consist of three quarks – are present in stars and in intergalactic gas in clusters of galaxies. Researchers have found that “a fraction 10−3 of all baryons may have formed luminous objects by z = 30”. This redshift shows the time when the age of the universe was about hundred million years at the Hubble constant of 67.3 km/s/Mpc and the matter density parameter of 0.315.
It has also been reported that about 10−6 of all baryons are present in stars at redshift z ∼ 24−19 and the stellar fraction in baryons 10−3 is reached later, at z ∼ 15 − 14. These numbers showed that the fraction of baryonic matter in early stars was very low.
Black holes are objects in space thought to contain some celestial object with such a strong gravitational pull that no matter or energy can escape from it. Black holes are believed to form when stars collapse in upon themselves.
Scientists are of the opinion that black holes are present in almost every large galaxy and in some relatively smaller galaxies.
Usually, the mass of black holes is smaller in spiral galaxies and is correlated with the bulge mass. Mass of black holes may vary from ten billion solar masses in giant elliptical and compact lenticular galaxies to a few million solar masses in spiral galaxies such as Milky Way (MW). Although the mass of the black hole is considered to be about 0.1% of the mass of the stellar bulge of the galaxy but rare chances are there as for example NGC 1277 has the central black hole of 1.7×1010 solar masses or about 60% of its bulge mass.
A. D. Dolgov, & S. I. Blinnikov (2013). Stars and Black Holes from the very Early Universe arXiv arXiv: 1309.3395v1