167 research outputs found
Distribution of binary mergers around galaxies
We use a stellar binary population synthesis code to find the lifetimes and
velocities of several types of possible GRB progenitors: double neutron stars,
black hole neutron stars, black hole white dwarfs, helium star mergers.
Assuming that they are born in different types of galaxies we compute their
spatial distribution and compare it with the observed locations of GRB
afterglows within their hosts. We discuss constraints on the compact object
merger model of GRBs imposed by this comparison and find that the observations
of afterglows and their host galaxies appear inconsistent with the GRB compact
object merger model.Comment: 5 pages, 2 figures, Latex with aipproc.sty, Proc. of the 5th
Huntsville Gamma Ray Burst Symposium, Oct. 1999, ed. R.M. Kippen, AI
IC10~X-1/NGC300~X-1: the very immediate progenitors of BH-BH binaries
We investigate the future evolution of two extragalactic X-ray binaries: IC10
X-1 and NGC300 X-1. Each of them consists of a high mass BH (\sim 20-30
\msun) accreting from a massive WR star companion (\gtrsim 20 \msun), and
both are located in low metallicity galaxies. We analyze the current state of
the systems and demonstrate that both systems will very quickly (
Myr) form close BH-BH binaries with the short coalescence time ( Gyr)
and large chirp mass (\sim 15 \msun). The formation of BH-BH system seems
unavoidable, as {\em (i)} WR companions are well within their Roche lobes and
they do not expand so no Roche lobe overflow is expected, {\em (ii)} even
intense WR wind mass loss does not remove sufficient mass to prohibit the
formation of the second BH, {\em (ii)} even if BH receives the large natal
kick, the systems are very closely bound and are almost impossible to disrupt.
As there are two such immediate BH-BH progenitor systems within 2 Mpc and as
the current gravitational wave instruments LIGO/VIRGO (initial stage) can
detect such massive BH-BH mergers out to Mpc, the empirically
estimated detection rate of such inspirals is at the
99% confidence level. If there is no detection in the current LIGO/VIRGO data
(unreleased year of run), the existence of these two massive BH systems
poses an interesting challenge. Either the gravitational radiation search is
not sensitive to massive inspirals or there is some fundamental
misunderstanding of stellar evolution physics leading directly to the formation
of BH-BH binaries.Comment: 9 pages, resubmitted to ApJ with major extensio
Looking for GRB progenitors
Using stellar binary population synthesis code we calculate the production
rates and lifetimes of several types of possible GRB progenitors. We consider
mergers of double neutron stars, black hole neutron stars, black hole white
dwarfs and helium star mergers. We calibrate the results with the measured star
formation rate history. We discuss the viability of each GRB model, and
alternatively assuming that all bursts are connected with one model we
constrain the required collimation of GRBs. We also show the importance of
widely used evolutionary parameters on the merger rates of calculated binary
populations.Comment: 5 pages, 2 figures, Latex with aipproc.sty, Proc. of the 5th
Huntsville Gamma Ray Burst Symposium, Oct. 1999, ed. R.M. Kippen, AI
The influence of the distribution of cosmic star formation at different metallicities on the properties of merging double compact objects
Binaries that merge within the local Universe originate from progenitor
systems that formed at different times and in various environments. The
efficiency of formation of double compact objects is highly sensitive to
metallicity of the star formation. Therefore, to confront the theoretical
predictions with observational limits resulting from gravitational waves
observations one has to account for the formation and evolution of progenitor
stars in the chemically evolving Universe. In particular, this requires
knowledge of the distribution of cosmic star formation rate at different
metallicities and times, probed by redshift (SFR(Z,z)). We investigate the
effect of the assumed SFR(Z,z) on the properties of merging double compact
objects, in particular on their merger rate densities. Using a set of binary
evolution models from Chruslinska et al. (2018) we demonstrate that the
reported tension between the merger rates of different types of double compact
objects and current observational limits in some cases can be resolved if a
SFR(Z,z) closer to that expected based on observations of local star-forming
galaxies is used, without the need for changing the assumptions about the
evolution of progenitor stars of different masses. This highlights the
importance of finding tighter constraints on SFR(Z,z) and understanding the
associated uncertainties.Comment: 6 pages, 4 figures, resubmitted to MNRAS after minor revisio
Stellar Mergers Are Common
The observed Galactic rate of stellar mergers or the initiation of common
envelope phases brighter than M_V=-3 (M_I=-4) is of order 0.5 (0.3)/year with
90% confidence statistical uncertainties of 0.24-1.1 (0.14-0.65) and factor of
2 systematic uncertainties. The (peak) luminosity function is roughly dN/dL
L^(-1.4+/-0.3), so the rates for events more luminous than V1309 Sco (M_V=-7
mag) or V838Mon (M_V=-10 mag) are lower at r~0.1/year and 0.03/year,
respectively. The peak luminosity is a steep function of progenitor mass, L
M^(2-3). This very roughly parallels the scaling of luminosity with mass on the
main sequence, but the transients are ~2000-4000 times more luminous at peak.
Combining these, the mass function of the progenitors, dN/dM M^(-2.0+/-0.8), is
consistent with the initial mass function, albeit with broad uncertainties.
These observational results are also broadly consistent with the estimates of
binary population synthesis models. While extragalactic variability surveys can
better define the rates and properties of the high luminosity events,
systematic, moderate depth (I>16 mag) surveys of the Galactic plane are needed
to characterize the low luminosity events. The existing Galactic samples are
only ~20% complete and Galactic surveys are (at best) reaching a typical
magnitude limit of <13 mag.Comment: Submitted to MNRAS (13 pages, 6 figures, 3 tables
- …