* Astronomy

Planck telescope puts new datestamp on first stars

Scientists working on Europe's Planck satellite say the first stars in the Universe lit up later than was previously thought.
The team has made the most precise map of the "oldest light" in the cosmos.
Earlier observations of this radiation had suggested that the first generation of stars burst into life about 420 million years after the Big Bang.
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Title: Dust Production Factories in the Early Universe: Formation of Carbon Grains in Red-supergiant Winds of Very Massive Population III Stars
Author: Takaya Nozawa, Sung-Chul Yoon, Keiichi Maeda, Takashi Kozasa, Ken'ichi Nomoto, Norbert Langer

We investigate the formation of dust in a stellar wind during the red-supergiant (RSG) phase of a very massive Population III star with the zero-age main sequence mass of 500 M_sun. We show that, in a carbon-rich wind with a constant velocity, carbon grains can form with a lognormal-like size distribution, and that all of the carbon available for dust formation finally condense into dust for wide ranges of the mass-loss rate ((0.1-3) x 10^{-3} solar masses yr^{-1}) and wind velocity (1-100 km s^{-1}). We also find that the acceleration of the wind driven by newly formed dust suppresses the grain growth but still allows more than half of gas-phase carbon to be finally locked up in dust grains. These results indicate that at most 1.7 solar masses of carbon grains can form in total during the RSG phase of 500 solar masses Population III stars. Such a high dust yield could place very massive primordial stars as important sources of dust at the very early epoch of the universe if the initial mass function of Population III stars was top-heavy. We also briefly discuss a new formation scenario of carbon-rich ultra-metal-poor stars considering the feedback from very massive Population III stars.

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Title: Formation of the First Stars
Authors: Volker Bromm

Understanding the formation of the first stars is one of the frontier topics in modern astrophysics and cosmology. Their emergence signalled the end of the cosmic dark ages, a few hundred million years after the Big Bang, leading to a fundamental transformation of the early Universe through the production of ionising photons and the initial enrichment with heavy chemical elements. We here review the state of our knowledge, separating the well understood elements of our emerging picture from those where more work is required. Primordial star formation is unique in that its initial conditions can be directly inferred from the Lambda Cold Dark Matter (LCDM) model of cosmological structure formation. Combined with gas cooling that is mediated via molecular hydrogen, one can robustly identify the regions of primordial star formation, the so-called minihalos, having total masses of ~10^6 solar masses and collapsing at redshifts z~20-30. Within this framework, a number of studies have defined a preliminary standard model, with the main result that the first stars were predominantly massive. This model has recently been modified to include a ubiquitous mode of fragmentation in the protostellar disks, such that the typical outcome of primordial star formation may be the formation of a binary or small multiple stellar system. We will also discuss extensions to this standard picture due to the presence of dynamically significant magnetic fields, of heating from self-annihilating WIMP dark matter, or cosmic rays. We conclude by discussing possible strategies to empirically test our theoretical models.

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Title: The Biggest Explosions in the Universe
Authors: Jarrett L. Johnson (LANL), Daniel J. Whalen (LANL, Heidelberg ITA), Wesley Even (LANL), Chris L. Fryer (LANL), Alex Heger (Monash), Joseph Smidt (LANL), Ke-Jung Chen (Minnesota)

Supermassive primordial stars are expected to form in a small fraction of massive protogalaxies in the early universe, and are generally conceived of as the progenitors of the seeds of supermassive black holes (BHs) at high redshift. Supermassive stars with masses of ~ 55,000 solar masses, however, have been found to explode and completely disrupt in a supernova (SN) with an energy of up to ~ 10^55 erg, instead of collapsing to a BH. Such events, roughly 10,000 times more energetic than typical SNe today, would be among the biggest explosions in the history of the universe. We carry out a simulation of such a supermassive star SN in two stages. Using the RAGE radiation hydrodynamics code we first evolve the explosion from the earliest stages, through the breakout of the shock from the surface of the star until the blast wave has propagated out to several parsecs from the explosion site, which lies deep within an atomic cooling dark matter (DM) halo at z ~ 15. Then, using the GADGET cosmological hydrodynamics code we evolve the explosion out to several kiloparsecs from the explosion site, far into the low-density intergalactic medium. The host DM halo, with a total mass of 4 x 10^7 solar masses, much more massive than typical primordial star-forming halos, is completely evacuated of high density gas after < 10 Myr, although dense metal-enriched gas recollapses into the halo, where it will likely form second-generation stars after > 70 Myr. The ~ 20,000 solar masses in metals that are released in the explosion are widely distributed, and enrich the dense recollapsing gas to an average metallicity of ~ 0.05 Z_Sun. Such a high level of enrichment suggests that the chemical signature of these supermassive star explosions may have been missed in previous surveys of metal-poor stars.

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