661 research outputs found
Event Rates for Binary Inspiral
Double compact objects (neutron stars and black holes) found in binaries with
small orbital separations are known to spiral in and are expected to coalesce
eventually because of the emission of gravitational waves. Such inspiral and
merger events are thought to be primary sources for ground based
gravitational-wave interferometric detectors (such as LIGO). Here, we present a
brief review of estimates of coalescence rates and we examine the origin and
relative importance of uncertainties associated with the rate estimates. For
the case of double neutron star systems, we compare the most recent rate
estimates to upper limits derived in a number of different ways. We also
discuss the implications of the formation of close binaries with two
non-recycled pulsars.Comment: 12 pages, to appear in AIP proceedings ``Astrophysical Sources of
Gravitational Radiation for Ground-Based Detectors.'
Constraining Binary Evolution with Gravitational Wave Measurements of Chirp Masses
Using the StarTrack binary population synthesis code we investigate the
properties of population of compact object binaries. Taking into account the
selection effects we calculate the expected properties of the observed
binaries.We analyze possible constraints on the stellar evolution models and
find that an observed sample of about one hundred mergers will yield strong
constraints on the binary evolution scenarios.Comment: Invited talk at "The Astrophysics of Gravitational Wave Sources"
Workshop; April 24-26, 2003, U. Maryland; 10 page
The distribution of mass ratios in compact object binaries
Using the StarTrack population synthesis code we compute the distribution of
masses of merging compact object (black hole or neutron star) binaries. The
shape of the mass distribution is sensitive to some of the parameters governing
the stellar binary evolution. We discuss the possibility of constraining
stellar evolution models using mass measurements obtained from the detection of
compact object inspiral with the upcoming gravitational-wave observatories.Comment: 10 pages, uses spie.cls, Proc of the SPIE Conference "Astronomical
Telescopes and Instrumentation
Merger rates of double neutron stars and stellar origin black holes: The Impact of Initial Conditions on Binary Evolution Predictions
The initial mass function (IMF), binary fraction and distributions of binary
parameters (mass ratios, separations and eccentricities) are indispensable
input for simulations of stellar populations. It is often claimed that these
are poorly constrained significantly affecting evolutionary predictions.
Recently, dedicated observing campaigns provided new constraints on the initial
conditions for massive stars. Findings include a larger close binary fraction
and a stronger preference for very tight systems. We investigate the impact on
the predicted merger rates of neutron stars and black holes.
Despite the changes with previous assumptions, we only find an increase of
less than a factor 2 (insignificant compared with evolutionary uncertainties of
typically a factor 10-100). We further show that the uncertainties in the new
initial binary properties do not significantly affect (within a factor of 2)
our predictions of double compact object merger rates. An exception is the
uncertainty in IMF (variations by a factor of 6 up and down). No significant
changes in the distributions of final component masses, mass ratios, chirp
masses and delay times are found.
We conclude that the predictions are, for practical purposes, robust against
uncertainties in the initial conditions concerning binary parameters with
exception of the IMF. This eliminates an important layer of the many uncertain
assumptions affecting the predictions of merger detection rates with the
gravitational wave detectors aLIGO/aVirgo.Comment: Accepted for publication in Ap
Bounds on Expected Black Hole Spins in Inspiraling Binaries
As a first step towards understanding the angular momentum evolution history
of black holes in merging black-hole/neutron-star binaries, we perform
population synthesis calculations to track the distribution of accretion
histories of compact objects in such binaries. We find that there are three
distinct processes which can possibly contribute to the black-hole spin
magnitude: a birth spin for the black hole, imparted at either (i) the collapse
of a massive progenitor star to a black hole or (ii) the accretion-induced
collapse of a neutron star to a black hole; and (iii) an accretion spin-up when
the already formed black hole [via (i) or (ii)] goes through an accretion
episode (through an accretion disk or a common-envelope phase). Our results
show that, with regard to accretion-induced spinup in merging BH-NS binaries
[method (iii) above], only
{\em accretion episodes associated with common-envelope phases and
hypercritical accretion rates} occur in the formation history of merging black
hole/neutron star binaries. Lacking unambiguous experimental information about
BH birth spins [i.e., regarding the results of processes (i) and (ii)], we
choose two fiducial values for the BH birth angular momentum parameter a=J/M^2,
consistent with observations of (i) NS birth spins (a roughly 0) and (ii) X-ray
binaries (a=0.5). Using these two fiducial values and a conservative upper
bound on the specific angular momentum of accreted matter, we discuss the
expected range of black hole spins in the binaries of interest. We conclude
with comments on the significance of these results for ground-based
gravitational-wave searches of inspiral signals from black hole binaries.Comment: Submitted to ApJ. (v1) Uses emulateapj.cls. 5 figures. (v2):
corrected reference list and uses smaller figures (v3): Includes changes in
response to referee comments, including new discussion of XRBs. Figures
merged, so only 3 figures (v4) Minor typo correction, plus updated abstract
posted onlin
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