176 research outputs found
Gravitational wave background from coalescing compact stars in eccentric orbits
Stochastic gravitational wave background produced by a stationary coalescing
population of binary neutron stars in the Galaxy is calculated. This background
is found to constitute a confusion limit within the LISA frequency band up to a
limiting frequency \NUlim{}\sim 10^{-3} Hz, leaving the frequency window
-- Hz open for the potential detection of cosmological
stochastic gravitational waves and of signals involving massive black holes out
to cosmological distances.Comment: 6 pages, 7 figure
Rapidly rotating neutron star progenitors
Rotating proto-neutron stars can be important sources of gravitational waves
to be searched for by present-day and future interferometric detectors. It was
demonstrated by Imshennik that in extreme cases the rapid rotation of a
collapsing stellar core may lead to fission and formation of a binary
proto-neutron star which subsequently merges due to gravitational wave
emission. In the present paper, we show that such dynamically unstable
collapsing stellar cores may be the product of a former merger process of two
stellar cores in a common envelope. We applied population synthesis
calculations to assess the expected fraction of such rapidly rotating stellar
cores which may lead to fission and formation of a pair of proto-neutron stars.
We have used the BSE population synthesis code supplemented with a new
treatment of stellar core rotation during the evolution via effective
core-envelope coupling, characterized by the coupling time, . The
validity of this approach is checked by direct MESA calculations of the
evolution of a rotating 15 star. From comparison of the calculated
spin distribution of young neutron stars with the observed one, reported by
Popov and Turolla, we infer the value years. We
show that merging of stellar cores in common envelopes can lead to collapses
with dynamically unstable proto-neutron stars, with their formation rate being
of the total core collapses, depending on the common envelope
efficiency.Comment: 10 pages, 4 figures, accepted for publication in MNRA
A young contracting white dwarf in the peculiar binary HD 49798/RX J0648.0--4418?
HD 49798/RX J0648.0--4418 is a peculiar X-ray binary with a hot subdwarf
(sdO) mass donor. The nature of the accreting compact object is not known, but
its spin period ~s and s~s, prove
that it can be only either a white dwarf or a neutron star. The spin-up has
been very stable for more than 20 years. We demonstrate that the continuous
stable spin-up of the compact companion of HD 49798 can be best explained by
contraction of a young white dwarf with an age ~Myrs. This allows us to
interpret all the basic parameters of the system in the framework of an
accreting white dwarf. We present examples of binary evolution which result in
such systems. If correct, this is the first direct evidence for a white dwarf
contraction on early evolutionary stages.Comment: 9 pages, accepted to MNRA
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