375 research outputs found
Formation Of The First Galaxies
The emergence of the first stars and galaxies ended the cosmic dark ages, thus fundamentally transforming the simple initial state of the universe into one of ever increasing complexity. We will review the basic physics governing the formation of the first galaxies. Their properties sensitively depend on the feedback exerted by the first, Population III, stars, which in turn reflects how massive those stars were. The key goal is to derive their observational signature, to be probed with upcoming next-generation facilities, such as the James Webb Space Telescope.Astronom
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GRB Cosmology: Probing The Early Universe
Current observations are about to open up a direct observational window into the final frontier of cosmology: the crucial first billion years in cosmic history when the first stars and galaxies formed. Even before the launch of the James Webb Space Telescope, it would be possible to utilize Gamma-Ray Bursts (GRBs) as unique probes of cosmic star formation and the state of the intergalactic medium up to redshifts of the first stars. The ongoing Swift mission might be the first observatory to detect individual Population III stars, provided that massive metal-free stars were able to trigger GRBs. Swift will empirically constrain the redshift at which Population III star formation was terminated, thus providing crucial input to models of cosmic reionization and metal enrichment.Astronom
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Assembly Of The First Dwarf Galaxies
Understanding the formation and evolution of the first stars and galaxies is crucial to understanding reionization, a key epoch in the history of the Universe. Detailed theoretical studies of the galaxies before and during reionization are now particularly urgent because of the wealth of observational data that will soon be provided by the next generation of telescopes, such as JWST, ALMA, LOFAR, MWA, and others. We simulate the formation of the first galaxies using cosmological smoothed particle hydrodynamics simulations. Zooming in on individual galaxies, we explore how various physical processes affect their assembly and further evolution. A highlight of our study will be the simulation of the radiation-hydrodynamics of galaxy assembly, which we will perform using our multi-frequency radiative transfer method TRAPHIC. Feedback from radiation has long been suspected to play a decisive role in galaxy formation and we will investigate its implications for observable properties of the first galaxies.Astronom
Impact of Cosmic Rays on Population III Star Formation
We explore the implications of a possible cosmic ray (CR) background
generated during the first supernova explosions that end the brief lives of
massive Population III stars. We show that such a CR background could have
significantly influenced the cooling and collapse of primordial gas clouds in
minihaloes around redshifts of z ~ 15 - 20, provided the CR flux was sufficient
to yield an ionization rate greater than about 10^-19 s^-1 near the center of
the minihalo. The presence of CRs with energies less than approximately 10^7 eV
would indirectly enhance the molecular cooling in these regions, and we
estimate that the resulting lower temperatures in these minihaloes would yield
a characteristic stellar mass as low as ~ 10 M_sun. CRs have a less pronounced
effect on the cooling and collapse of primordial gas clouds inside more massive
dark matter haloes with virial masses greater than approximately 10^8 M_sun at
the later stages of cosmological structure formation around z ~ 10 - 15. In
these clouds, even without CR flux the molecular abundance is already
sufficient to allow cooling to the floor set by the temperature of the cosmic
microwave background.Comment: MNRAS in press, 12 pages, 6 figure
The Formation of the First Low-Mass Stars From Gas With Low Carbon and Oxygen Abundances
The first stars in the Universe are predicted to have been much more massive
than the Sun. Gravitational condensation accompanied by cooling of the
primordial gas due to molecular hydrogen, yields a minimum fragmentation scale
of a few hundred solar masses. Numerical simulations indicate that once a gas
clump acquires this mass, it undergoes a slow, quasi-hydrostatic contraction
without further fragmentation. Here we show that as soon as the primordial gas
- left over from the Big Bang - is enriched by supernovae to a carbon or oxygen
abundance as small as ~0.01-0.1% of that found in the Sun, cooling by
singly-ionized carbon or neutral oxygen can lead to the formation of low-mass
stars. This mechanism naturally accommodates the discovery of solar mass stars
with unusually low (10^{-5.3} of the solar value) iron abundance but with a
high (10^{-1.3} solar) carbon abundance. The minimum stellar mass at early
epochs is partially regulated by the temperature of the cosmic microwave
background. The derived critical abundances can be used to identify those
metal-poor stars in our Milky Way galaxy with elemental patterns imprinted by
the first supernovae.Comment: 14 pages, 2 figures (appeared today in Nature
The Contribution of the First Stars to the Cosmic Infrared Background
We calculate the contribution to the cosmic infrared background from very
massive metal-free stars at high redshift. We explore two plausible
star-formation models and two limiting cases for the reprocessing of the
ionizing stellar emission. We find that Population III stars may contribute
significantly to the cosmic near-infrared background if the following
conditions are met: (i) The first stars were massive, with M > ~100 M_sun. (ii)
Molecular hydrogen can cool baryons in low-mass haloes. (iii) Pop III star
formation is ongoing, and not shut off through negative feedback effects. (iv)
Virialized haloes form stars at about 40 per cent efficiency up to the redshift
of reionization, z~7. (v) The escape fraction of the ionizing radiation into
the intergalactic medium is small. (vi) Nearly all of the stars end up in
massive black holes without contributing to the metal enrichment of the
Universe.Comment: 11 pages, 6 figures, expanded discussion, added mid-IR to Fig 6,
MNRAS in pres
Low-Mass Relics of Early Star Formation
The earliest stars to form in the Universe were the first sources of light,
heat and metals after the Big Bang. The products of their evolution will have
had a profound impact on subsequent generations of stars. Recent studies of
primordial star formation have shown that, in the absence of metals (elements
heavier than helium), the formation of stars with masses 100 times that of the
Sun would have been strongly favoured, and that low-mass stars could not have
formed before a minimum level of metal enrichment had been reached. The value
of this minimum level is very uncertain, but is likely to be between 10^{-6}
and 10^{-4} that of the Sun. Here we show that the recent discovery of the most
iron-poor star known indicates the presence of dust in extremely
low-metallicity gas, and that this dust is crucial for the formation of
lower-mass second-generation stars that could survive until today. The dust
provides a pathway for cooling the gas that leads to fragmentation of the
precursor molecular cloud into smaller clumps, which become the lower-mass
stars.Comment: Offprint of Nature 422 (2003), 869-871 (issue 24 April 2003
The First Supernovae: Source Density And Observability Of Pair Instability Supernovae
Theoretical models predict that some of the first stars ended their lives as extremely energetic Pair Instability Supernovae (PISNe). With energies approaching 10(53) erg, these supernovae are expected to be within the detection limits of the upcoming James Webb Space Telescope (JWST) allowing observational constraints to be placed on the properties of the first stars. We estimate the source density of PISNe using a semi-analytic Press-Schecter based approach informed by cosmological simulations, with an upper limit of similar to 0.2 PISNe visible per JWST field of view at any given time. We find that the main obstacle to observing PISNe is their scarcity rather than their faintness. Given this we suggest a mosaic style search strategy for detecting PISNe from the first stars.Astronom
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