The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and ...galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.
Recent theoretical studies have revealed the possibly important role of the capture and annihilation process of weakly interacting massive particles (WIMPs) for the first stars. Using new ...evolutionary models of metal-free massive stars, we investigate the impact of such 'dark matter burning' for the first stars in different environments of dark matter (DM) halos, in terms of the ambient WIMP density. We find that, in agreement with existing literature, stellar lifetimes can be significantly prolonged for a certain range of image (i.e., image with the current upper limit for the spin- dependent elastic scattering cross section image). This greatly enhances the role of rotationally induced chemical mixing in rotating stars, in favor of abundant production of primary nitrogen, massive helium stars, and long gamma-ray bursts, from the first stars. We also find that stars with image may not undergo nuclear burning stages, confirming the previous work, and that ionizing photon fluxes from such DM supported stars are very weak. Delayed metal enrichment and slow reionization in the early universe would have resulted if most of the first stars had been born in DM halos with such high image, unless it had been lowered significantly below the threshold for efficient DM burning on a short timescale.
The James Webb Space Telescope (JWST) is unveiling astounding results about the first few hundred million years of life of the Universe, delivering images of galaxies at very high redshifts. Here, we ...develop a UV luminosity function model for high-redshift galaxies, considering parameters such as the stellar formation rate, dust extinction, and halo mass function. Calibration of this luminosity function model using UV luminosity data at redshifts z = 4-7 yields optimal parameter values. Testing the model against data at higher redshifts reveals successful accommodation of the data at z = 8-9, but challenges emerge at z~13. Our findings suggest a negligible role of dust extinction at the highest redshifts, prompting a modification of the stellar formation rate to incorporate a larger fraction of luminous objects per massive halo, consistently with similar recent studies. This effect could be attributed to mundane explanations such as unknown evolution of standard astrophysics at high redshift or to the existence of exotic objects at high redshift. We comment on this latter possibility.
We perform a new estimate of the high energy neutrinos expected from GRBs associated with the first generation of stars in light of new models and constraints on the epoch of reionization and a more ...detailed evaluation of the neutrino emission yields. In disagreement with most optimistic results in previous literature, we find that high energy neutrinos from Population III stars will not be observable with current or near future neutrino telescopes. This rules them out as a viable diagnostic tool for these still elusive metal-free stars. We also perform an estimate of the flux at Earth of neutrinos from Dark Matter annihilation in the recently proposed 'Dark Stars' obtaining equally negative results; in particular the very low peak-energies of this flux buries it several orders of magnitude below the atmospheric ones. Similar considerations (with different backgrounds) apply to the gamma-ray background by DM annihilation.
Turbulence in the First Stars Iocco, Fabio
First Stars III (AIP Conference Proceedings Volume 990),
01/2008, Volume:
990
Journal Article
Peer reviewed
We present preliminary results of 2-D simulations of the effects of turbulence in the mixing of Pair Instability Supenovae. We make use of the FLASH code to evolve initial 1-D models of post-bounce ...PISNe and seed turbulence in form of velocity perturbations. We identify the energetic and spatial scale for the turbulence to have mixing effects on the metal shells inside the star. Under the conditions we examine, we observe some mixing but the onion structure of the metal distribution is not disrupted.
The first stars in the history of the universe are likely to form in the dense central regions of similar to 10(5)-10(6) M-circle dot cold dark matter halos at z approximate to 10-50. The ...annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive, and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that all dark stars with masses up to 10(3) M-circle dot are intrinsically too faint to be detected by JWST at z > 6. However, by exploiting foreground galaxy clusters as gravitational telescopes do, certain varieties of cool (T-eff <= 30,000 K) dark stars should be within reach at redshifts up to z approximate to 10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least similar to 1% of the total stellar mass in such objects.
We investigate the scenario in which primordial black holes (PBHs) with
masses Mpbh < 10^9 g undergo Hawking evaporation, around the Big-Bang
nucleosynthesis (BBN) epoch. The evaporation process ...modifies the Universe's
expansion rate and the baryon-to-photon ratio, leading to an alteration of the
primordial abundance of light nuclei. We present numerical solutions for the
set of equations describing this physics, considering different values of PBH
masses and abundances at their formation, showing how their evaporation impacts
the abundances of light nuclei, obtained by incorporating the non-standard
Hubble rate and baryon-to-photon ratio into the BBN code PArthENoPE. The
results are then used to place upper bounds for the PBH relative abundance at
formation in the range 10^8 g < Mpbh < 10^9 g, providing the strongest
constraints existing to-date in this mass range.
We present here a quantitative, accurate estimate of the impact of uncertainties of astrophysical nature on the determination of the dark matter distribution within our Galaxy, the Milky Way. Based ...on an update of a previous analysis, this work is motivated by recent new determinations of astrophysical quantities of relevance -- such as the Galactic parameters (R0,V0) -- from the GRAVITY collaboration and the GAIA satellite, respectively. We find that even with these state-of-the-art determination and a range of uncertainties -- both statistical and systematic -- much narrowed with respect to previous work, the uncertainties on the dark matter distribution and their impact on searches of physics beyond the standard model stays sizable.
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