168 research outputs found
Relativistic Binary Pulsars with Black-Hole Companions
Binaries containing a stellar-mass black hole and a recycled radio pulsar
have so far eluded detection. We present a focused investigation of the
formation and evolution of these systems in the Galactic disk, highlighting the
factors that limit their numbers and the reasons why they may be extremely
rare. We surmise that the birthrate of black-hole/recycled-pulsar binaries in
the Galactic disk is probably no higher than ~10^{-7}/yr, and may be much less.
Simple arguments regarding common-envelope evolution suggest that these
binaries should have orbital periods less than 10 hr and an average lifetime of
<~10^8 yr before coalescence due to the emission of gravitational radiation. We
expect that fewer than ~10 of these compact, relativistic binaries currently
reside in the Galactic disk, less than 0.1--1% of the number of double neutron
stars. The discovery of two or more black-hole/recycled-pulsar binaries using
current radio telescopes would tightly constrain certain ideas regarding the
evolution of massive stars, dynamical mass transfer, and black-hole formation.Comment: 10 pages, 6 figures, accepted by ApJ, minor change
X-ray astronomy experiments from sounding rockets
During the past fourteen years, the M.I.T. X-ray Astronomy sounding rocket group has designed, fabricated, and flown five different scientific sounding rocket payloads. These experiment payloads were launched on a total of twelve sounding rocket flights of which only one failed because of rocket problems. Eight of these flights yielded astronomical data that resulted in a total of twelve publications. The bulk of this research was supported by NASA Grant NGR 22-009-730 X-Ray Astronomy Experiments Sounding Rockets. The fifth and final experiment payload conceived and built under this Grant (the Wide Field Soft X-ray Camera: WFSXC) served as the prototype for the British Wide Field Camera (WFC) experiment to be launched on the ROSAT mission. The five experiment payloads and the results obtained from these experiments are briefly described. In the case of the WFSXC, which served principally as an engineering prototype for a major space mission, a number of papers written by British collaborators which describe the ROSAT Wide Field Camera are presented
Formation of Compact Binaries in Globular Clusters
We report here on two complementary population synthesis studies which relate
directly to the formation and evolution of neutron star binaries in globular
clusters. In the first, we compute the probability of retaining neutron stars
in globular clusters, and quantitatively confirm the idea that the retention
fraction for neutron stars born in binary systems is greatly enhanced over
those born in isolated stars. However, the retention fraction may well be
insufficient to explain the current population of neutron star binaries. In the
second study, we follow a large population of primordial binaries and neutron
stars throughout the lifetime of a globular cluster whose properties may be
similar to 47 Tuc. We directly compute all 3-body interactions among binary
systems, neutron stars, and isolated field stars throughout the history of the
cluster. The evolution of certain types of neutron star binaries is followed up
to the current epoch. The numbers of close, recycled, binary radio pulsars are
evaluated and compared with the results of radio observations.Comment: 14 pages; to appear in Evolution of Binary and Multiple Star Systems,
a Meeting in Celebration of Peter Eggleton's 60th Birthday, Bormio, Italy,
ASP Conference Series, eds. P. Podsiadlowski et a
Nova-induced mass transfer variations
We investigate variations of the mass transfer rate in cataclysmic variables
(CVs) that are induced by nova outbursts. The ejection of nova shells leads to
a spread of transfer rates in systems with similar orbital period. The effect
is maximal if the specific angular momentum in the shell is the same as the
specific orbital angular momentum of the white dwarf. We show analytically that
in this case the nova-induced widening of the mass transfer rate distribution
can be significant if the system, in the absence of nova outbursts, is close to
mass transfer instability (i.e., within a factor of ~1.5 of the critical mass
ratio). Hence the effect is negligible below the period gap and for systems
with high-mass white dwarfs. At orbital periods between about 3 and 6 hrs the
width of the mass transfer rate distribution exceeds an order of magnitude if
the mass accreted on the white dwarf prior to the runaway is larger than a few
10^{-4} M_sun. At a given orbital period in this range, systems with the
highest transfer rate should on average have the largest ratio of donor to
white dwarf mass. We show results of population synthesis models which confirm
and augment the analytic results.Comment: ApJ, in press; 14 pages (incl. 7 figures), emulateapj styl
Formation of Short-Period Binary Pulsars in Globular Clusters
We present a new dynamical scenario for the formation of short-period binary
millisecond pulsars in globular clusters. Our work is motivated by the recent
observations of 20 radio pulsars in 47 Tuc. In a dense cluster such as 47 Tuc,
most neutron stars acquire binary companions through exchange interactions with
primordial binaries. The resulting systems have semimajor axes in the range
\~0.1-1 AU and neutron star companion masses ~1-3 Msun. For many of these
systems we find that, when the companion evolves off the main sequence and
fills its Roche lobe, the subsequent mass transfer is dynamically unstable.
This leads to a common envelope phase and the formation of short-period neutron
star - white dwarf binaries. For a significant fraction of these binaries, the
decay of the orbit due to gravitational radiation will be followed by a period
of stable mass transfer driven by a combination of gravitational radiation and
tidal heating of the companion. The properties of the resulting short-period
binaries match well those of observed binary pulsars in 47 Tuc.Comment: To appear in ApJ Letters, slightly abbreviated version with only
minor change
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