1,895 research outputs found
The effect of metallicity on the detection prospects for gravitational waves
Data from the SDSS (300,000 galaxies) indicates that recent star formation
(within the last 1 billion years) is bimodal: half the stars form from gas with
high amounts of metals (solar metallicity), and the other half form with small
contribution of elements heavier than Helium (10-30% solar). Theoretical
studies of mass loss from the brightest stars derive significantly higher
stellar-origin BH masses (30-80 Msun) than previously estimated for sub-solar
compositions. We combine these findings to estimate the probability of
detecting gravitational waves (GWs) arising from the inspiral of double compact
objects. Our results show that a low metallicity environment significantly
boosts the formation of double compact object binaries with at least one BH. In
particular, we find the GW detection rate is increased by a factor of 20 if the
metallicity is decreased from solar (as in all previous estimates) to a 50-50
mixture of solar and 10% solar metallicity. The current sensitivity of the two
largest instruments to NS-NS binary inspirals (VIRGO: 9 Mpc; LIGO: 18) is not
high enough to ensure a first detection. However, our results indicate that if
a future instrument increased the sensitivity to 50-100 Mpc, a detection of GWs
would be expected within the first year of observation. It was previously
thought that NS-NS inspirals were the most likely source for GW detection. Our
results indicate that BH-BH binaries are 25-times more likely sources than
NS-NS systems and that we are on the cusp of GW detection.Comment: 4 pages of text, 2 figures, 2 tables (ApJ Letters, accepted
Gamma-ray binaries and related systems
After initial claims and a long hiatus, it is now established that several
binary stars emit high (0.1-100 GeV) and very high energy (>100 GeV) gamma
rays. A new class has emerged called 'gamma-ray binaries', since most of their
radiated power is emitted beyond 1 MeV. Accreting X-ray binaries, novae and a
colliding wind binary (eta Car) have also been detected - 'related systems'
that confirm the ubiquity of particle acceleration in astrophysical sources. Do
these systems have anything in common ? What drives their high-energy emission
? How do the processes involved compare to those in other sources of gamma
rays: pulsars, active galactic nuclei, supernova remnants ? I review the wealth
of observational and theoretical work that have followed these detections, with
an emphasis on gamma-ray binaries. I present the current evidence that
gamma-ray binaries are driven by rotation-powered pulsars. Binaries are
laboratories giving access to different vantage points or physical conditions
on a regular timescale as the components revolve on their orbit. I explain the
basic ingredients that models of gamma-ray binaries use, the challenges that
they currently face, and how they can bring insights into the physics of
pulsars. I discuss how gamma-ray emission from microquasars provides a window
into the connection between accretion--ejection and acceleration, while eta Car
and novae raise new questions on the physics of these objects - or on the
theory of diffusive shock acceleration. Indeed, explaining the gamma-ray
emission from binaries strains our theories of high-energy astrophysical
processes, by testing them on scales and in environments that were generally
not foreseen, and this is how these detections are most valuable.Comment: 71 pages, 23 figures, minor updates to text, references, figures to
reflect published versio
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