Renaissance: Formation of the first light sources in the Universe after the Dark Ages Justin Vandenbroucke, UC Berkeley Physics 290H, February 12, 2008

Timeline of light and dark CMB z ~ 1000: Last Scattering Surface Dark Ages z ~ 6-30: first stars and quasars, reionization begins Reionizaton complete neutral, dark not observed theory + sim’s ionized, light observed ionized, light observed

Were the first light sources quasars (SMBH) or stars? Quasars most distant observed objects But much brighter than stars: observational bias Moreover, first stars would have died by now (lifetime ~1 Myr) Indeed, no stars observed with low enough metallicity WMAP: reionization began z > ~15; farthest quasars z ~6 so stars must have come first? Standard model: –First stars z = –First quasars z = 6-10

First star formation follows naturally from cosmology z = 17 Structure formation simulation: 50 kpc field First stars will form at intersections (bright knots) Bromm 2004

First stars formation Easy initial conditions from cosmology + structure formation –no metals: only light elements from Big Bang Nucleosynthesis –therefore no dust –no radiation or wind from other stars –no ambient B fields Full 3D simulations have been done: adaptive mesh refinement (AMR) or smoothed particle hydrodynamics (SPH) Both methods agree! For formation, characteristic T ~ 200 K, n ~10 4 / cm 3 Formation in most massive of the DM halo mass distribution (~10 6 M sun )

Example simulation of first star (Abel, Bryan & Norman 2002) Assume initial conditions from  =0 CDM cosmology Adaptive mesh refinement (AMR) over 10 orders of magnitude from cosmological to stellar ~100 kpc to ~1 AU First allow cosmological structure formation (hierarchical merging) to z~20 Gas cools, sinks into DM well until self gravitating Dense core ~100 M sun contracts Analytically, expected fragmentation (problem!) but in full simulation, no fragmentation Halos are too cold to collapse by atomic H radiation Must cool by molecular H radiation Need enough molecular H, formed by electron collisions when density is sufficient

First star formation from collapsed molecular cloud Abel et al 2002

First stars from collapse of molecular cloud: Simulation by another group (Bate, Bonnell & Bromm) Movie:

When did first supermassive black holes form? Quasars observed to z = 6  first ones must have formed in first Gyr Challenge: how can you build such massive objects so quickly? Hard to form unless stars already present (more later) Formation likely started at z ~ 10

Possible seeds for SMBH’s 1)Direct collapse from molecular gas 2)Dense clusters of normal stars 3)Relativistic clusters of collisionless particles/stars 4)Self interacting dark matter halos

SMBH from direct collapse of gas cloud Need to suppress star formation in cloud because SNe increase kinetic energy Need to cool via atomic H and not molecular H, due to the temperature of these clouds Possible if stars have already formed! (in other places, not the cloud) Then UV light dissociates molecular H

SMBH from collapse of star clusters stars evolve into mass segregation time radius in cluster heavy stars migrate in light stars migrate out Rasio et al. 2003

SMBH formation from dense star clusters initial state = gas of collisionless particles rings are spherical light flashes Final state = BH rings trapped Shapiro 2004 full GR simulation

SMBH from collapse of star clusters by runaway collisions Condition: cluster must collapse before its massive stars do initial central density velocity dispersion total mass

Conclusions First star and quasar formation limited to theory and simulation (with some observational constraints) Standard model: –stars z ~ –quasars z ~ 6-10 First star formation a natural outcome of standard cosmological structure formation Detailed numerical simulations using very different methods agree First SMBH formation a more difficult problem Direct collapse from molecular clouds vs. collapse of star clusters