Katharina Wollenberg

Katharina Wollenberg (Germany)

K.Wollenberg @ stud.uni-heidelberg.de

Modelling First Star Formation 

About 200 Myr after the big bang, the formation of the first stars (Population III, or Pop III stars) ended the cosmic epoch of the Dark Ages and cosmological reionization began: Our universe was gradually transformed into the hot and transparent cosmic web structure of galaxies we observe today.
Modern multidimensional simulations suggest that the first stars formed between redshift z ~ 20-30 in minihalos, which are small pre-galactic structures of mass > 10^5 M_sun. Depending on particular formation settings and relevant physical processes, such as accretion, fragmentation, mergers, radiation feedback or magnetic fields, primordial stars appear to have been created both solitarily and in binary or multiple stellar systems. Individual Pop III stars might have masses of several tens up to several thousand solar.
Pop III stars were also the first great nucleosynthetic engines of our universe, enriching the cosmos with the first heavy elements and radically altering the properties of later generations of stars. Besides, these first stars may also be the origin of the supermassive black holes found at the centres of most massive galaxies today.
However, in spite of their importance to structure formation in the early universe, little is known for certain about the first stars, and for now we must rely mostly on numerical simulations to understand their properties.
The aim of my PhD thesis is to perform numerical simulations on the formation of the first stars with the ZEUS-MP and Enzo codes to achieve a better understanding of their properties. I am developing numerical models of UV breakout from Pop III protostellar disks to see when ionizing radiation from nascent stars terminates accretion and determines their final masses. I am also investigating the effect of primeval magnetic fields on the stability of these disks to determine if they promote or suppress fragmentation and the formation of multiple stars.  With colleagues at UC Santa Cruz, we are additionally developing simulations of second generation star formation in the debris of the first supernova explosions to understand the properties of stars in primitive galaxies.

Supervisors: Simon Glover / Ralf Klessen (ITA)

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