879 research outputs found
Black hole demography at the dawn of gravitational-wave astronomy: State-of-The art and future perspectives
No full textThe first four LIGO detections have confirmed the existence of massive black holes (BHs), with mass 30-40 Mo. Such BHs might originate from massive metal-poor stars (Z < 0:3 Zo) or from gravitational instabilities in the early Universe. The formation channels of merging BHs are still poorly constrained. The measure of mass, spin and redshift distribution of merging BHs will give us fundamental clues to distinguish between different models. In parallel, a better understanding of several astrophysical processes (e.g. common envelope, core-collapse SNe, and dynamical evolution of BHs) is decisive, to shed light on the formation channels of merging BHs
X-ray binaries powered by massive stellar black holes
No full textThe mass of stellar black holes (BHs) is currently thought to be in the 3-20 M_☉ range, but is highly uncertain: recent observations indicate the existence of at least one BH with mass 〉20 M_☉. The metallicity of the progenitor star strongly influences the mass of the remnant, as only metal-poor stars can have a final mass higher than ̃{}40 M_☉, and are expected to directly collapse into BHs with mass 〉25 M_☉. By means of N-body simulations, we investigate the formation and evolution of massive stellar BHs (MSBHs, with mass 〉25 M_☉) in young dense star clusters. We study the effects of MSBHs on the population of X-ray sources
Relic Signatures of Reionization Sources
Full text linkWe have exploited the recent determination of the radial distribution of BSS in
four GCs, in order to investigate which mechanism of BSS formation prevails in these stellar
systems. Our conclusion is that the two main formation paths proposed so far, i.e. masstransfer
in PBs and merging of MS stars due to collisions in the cluster core, must coexist
and have similar efficiency both in a low density cluster (M3) and in much denser clusters,
like 47 Tuc and NGC 6752.
In particular, in M3, 47 Tuc, and NGC 6752 the COL-BSS sum to around 50 - 60% of
the total and mostly reside in the central region of the cluster. The MT-BSS are slightly
less abundant than the COL-BSS, but populate all the GC. The density of BSS reaches a minimum in a so-called zone of avoidance, which separates the portion of the GC mostly
occupied by COL-BSS from the cluster outskirts, where the MT-BSS dominate. The location
of the zone of avoidance is explained by accounting for the effects of the dynamical
friction on the PBs which were massive enough for generating the observed BSS.
The picture described above can also be applied to ! Cen; but in this case the lack
of a central peak in the BSS radial distribution requires that the large majority of the BSS
derive from PBs. The very low rate of production of COL-BSS could be in turn attributed
to the fact that mass segregation has not yet driven a sizeable number of PBs to the central
region of the cluster to produce BSS.
A very interesting further development of this research will be to perform a comparison
between the location of a significant sample of BSS in a GC and their spectroscopic
properties. According to the findings of this work, the position in the GC might represent
a strong dynamical clue for the formation mechanism of a given BSS. If it is located outside
the zone of avoidance, the BSS almost certainly results from evolution of a PB; if it
is harbored in the cluster core, the BSS has most likely a collisional origin. On the other
hand, indication about the origin of the same BSS can be independently obtained from high
resolution spectroscopy. Indeed the chemical signature of the MT-BSS formation process
has been recently discovered in 47 Tuc (Ferraro et al. 2006b). The acquisition of similar
sets of data in clusters with different structural parameters and/or in different regions of
the same cluster will provide an unprecedented tool for conforming the scenario presented
here and to finally address the BSS formation processes and their complex interplay with
the dynamical evolution of the cluster
The progenitors of compact-object binaries: impact of metallicity, common envelope and natal kicks
No full textThe cosmic merger rate of neutron stars and black holes
No full textSix gravitational wave detections have been reported so far, providing crucial insights on the merger rate of double compact objects. We investigate the cosmic merger rate of double neutron stars (DNSs), neutron star black hole binaries (NSBHs), and black hole binaries (BHBs) by means of population-synthesis simulations coupled with the Illustris cosmological simulation. We have performed six different simulations, considering different assumptions for the efficiency of common envelope (CE) ejection and exploring two distributions for the supernova (SN) kicks. The current BHB merger rate derived from our simulations spans from ~150 to ~240 Gpc-3 yr-1 and is only mildly dependent on CE efficiency. In contrast, the current merger rates of DNSs (ranging from ~20 to ~600 Gpc-3 yr-1) and NSBHs (ranging from~10 to~100 Gpc-3 yr-1) strongly depend on the assumptions on CE and natal kicks. The merger rate of DNSs is consistent with the one inferred from the detection of GW170817 only if a high ..
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