Enlightenment of the universe: the interplay between dark energy, the first stars and black holes

PhD ceremony: Ms. A. Aykutalp, 14.30 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Enlightenment of the universe: the interplay between dark energy, the first stars and black holes

Promotor(s): prof. M. Spaans

Faculty: Mathematics and Natural Sciences

In her thesis Aycin Aykutalp studies the nature of dark energy, effects of ultraviolet background and X-ray radiation on the formation of the first stars and galaxies with the supermassive black holes (SMBHs) in their centers.

The recent time acceleration in the expansion of the universe is often referred to as Dark energy (DE). DE constitutes 73% of the universe however the nature of it is still to be understood. I study the proposed connection between the DE density and the total number of black holes (BHs) in the universe and found that the DE density increases by a factor of 5 from redshift z=3-1 with the increase in the total number of macroscopic BHs in the universe.

The first stars have masses of 10-100 Msolar, whereas the present day stellar mass scale is ~1 Msolar. In order to understand this transition I ran simulations and found that the metal-poor star-forming ISM is fragile to UV radiation, and inclusion of a constant radiation background (F_0), raises the critical metallicity value for this transition from Z_cr~10^{-3.5} Z_solar to Z_cr~10^{-2} Z_solar when F_0> 10^{-5}$ erg s^{-1} cm^{-2}.

Observations of high z>6 quasars suggest that they are powered by SMBHs with masses on the order of 10^9 M_solar. I investigate the possible hosts of these SMBHs by performing cosmological simulations and found that, in the singular collapse seed BH scenario, under the influence of high UV background radiation, the central BH cannot yield the progenitors of z>6 SMBHs.