1,720,988 research outputs found
SIGNATURES OF PLANETS AND PROTOPLANETS IN THE GALACTIC CENTER: A CLUE TO UNDERSTANDING THE G2 CLOUD?
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Adaptive mesh refinement simulations of collisional ring galaxies: effects of the interaction geometry.
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Dynamics of stellar black holes in young star clusters with different metallicities - I. Implications for X-ray binaries.
Full text linkWe present N-body simulations of intermediate-mass (3000-4000M⊙) young star clusters (SCs) with three different metallicities (Z = 0.01, 0.1 and 1 Z⊙), including metal-dependent stellar evolution recipes and binary evolution. Following recent theoretical models of wind mass-loss and core-collapse supernovae, we assume that the mass of the stellar remnants depends on the metallicity of the progenitor stars. In particular, massive metal-poor stars (Z = 0.3 Z⊙) are enabled to form massive stellar black holes (MSBHs, with mass=25M⊙) through direct collapse. We find that three-body encounters, and especially dynamical exchanges, dominate the evolution of the MSBHs formed in our simulations. In SCs with Z = 0.01 and 0.1 Z⊙, about 75 per cent of simulated MSBHs form from single stars and become members of binaries through dynamical exchanges in the first 100 Myr of the SC life. This is a factor of ⊙3 more efficient than in the case of low-mass (<25M⊙) stellar black holes. A small but non-negligible fraction of MSBHs power wind-accreting (10-20 per cent) and Roche lobe overflow (RLO, 5-10 per cent) binary systems. The vast majority of MSBH binaries that undergo wind accretion and/or RLO were born from dynamical exchange. This result indicates that MSBHs can power X-ray binaries in low-metallicity young SCs, and is very promising to explain the association of many ultraluminous X-ray sources with low-metallicity and actively star-forming environments. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Impact of dark matter decays and annihilations on structure formation
Full text linkWe derived the influence of dark matter (DM) decays and annihilations on structure formation. The energy deposited by DM decays and annihilations into metal free halos both increases the gas temperature and enhances the formation of molecules. Within the primordial halos the temperature increase generally dominates over the molecular cooling, slightly delaying the collapse. In fact, the critical mass for collapse is generally higher than in the unperturbed case, when we consider the energy input from DM. In presence of DM decays and/or annihilations the fraction of baryons inside collapsed metal free halos should be slightly less (≈ 0.4) than the expected cosmological value
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