953 research outputs found
On Discovering Electromagnetic Emission from Neutron Star Mergers: The Early Years of Two Gravitational Wave Detectors
We present the first simulation addressing the prospects of finding an
electromagnetic (EM) counterpart to gravitational wave detections (GW) during
the early years of only two advanced interferometers. The perils of such a
search may have appeared insurmountable when considering the coarse ring-shaped
GW localizations spanning thousands of deg^2 using time-of-arrival information
alone. We show that leveraging the amplitude and phase information of the
predicted GW signal narrows the localization to arcs with a median area of only
~250 deg^2, thereby making an EM search tractable. Based on the locations and
orientations of the two LIGO detectors, we find that the GW sensitivity is
limited to one polarization and thus to only two sky quadrants. Thus, the rates
of GW events with two interferometers is only ~40% of the rate with three
interferometers of similar sensitivity. Another important implication of the
sky quadrant bias is that EM observatories in North America and Southern Africa
would be able to systematically respond to GW triggers several hours sooner
than Russia and Chile. Given the larger sky areas and the relative proximity of
detected mergers, 1m-class telescopes with very wide-field cameras are well
positioned for the challenge of finding an EM counterpart. Identification of
the EM counterpart amidst the even larger numbers of false positives further
underscores the importance of building a comprehensive catalog of foreground
stellar sources, background AGN and potential host galaxies in the local
universe.Comment: Submitted to ApJL, 8 pages, 4 figures, 1 tabl
Numerical simulations of neutron star-black hole binaries in the near-equal-mass regime
Simulations of neutron star-black hole (NSBH) binaries generally consider
black holes with masses in the range , where we expect to find
most stellar mass black holes. The existence of lower mass black holes,
however, cannot be theoretically ruled out. Low-mass black holes in binary
systems with a neutron star companion could mimic neutron star-neutron (NSNS)
binaries, as they power similar gravitational wave (GW) and electromagnetic
(EM) signals. To understand the differences and similarities between NSNS
mergers and low-mass NSBH mergers, numerical simulations are required. Here, we
perform a set of simulations of low-mass NSBH mergers, including systems
compatible with GW170817. Our simulations use a composition and temperature
dependent equation of state (DD2) and approximate neutrino transport, but no
magnetic fields. We find that low-mass NSBH mergers produce remnant disks
significantly less massive than previously expected, and consistent with the
post-merger outflow mass inferred from GW170817 for moderately asymmetric mass
ratio. The dynamical ejecta produced by systems compatible with GW170817 is
negligible except if the mass ratio and black hole spin are at the edge of the
allowed parameter space. That dynamical ejecta is cold, neutron-rich, and
surprisingly slow for ejecta produced during the tidal disruption of a neutron
star : . We also find that the final mass of the remnant
black hole is consistent with existing analytical predictions, while the final
spin of that black hole is noticeably larger than expected -- up to for our equal mass case
A Unique Multi-Messenger Signal of QCD Axion Dark Matter
We propose a multi-messenger probe of QCD axion Dark Matter based on
observations of black hole-neutron star binary inspirals. It is suggested that
a dense Dark Matter spike may grow around intermediate mass black holes
(). The presence of such a spike produces
two unique effects: a distinct phase shift in the gravitational wave strain
during the inspiral and an enhancement of the radio emission due to the
resonant axion-photon conversion occurring in the neutron star magnetosphere
throughout the inspiral and merger. Remarkably, the observation of the
gravitational wave signal can be used to infer the Dark Matter density and,
consequently, to predict the radio emission. We study the projected reach of
the LISA interferometer and next-generation radio telescopes such as the Square
Kilometre Array. Given a sufficiently nearby system, such observations will
potentially allow for the detection of QCD axion Dark Matter in the mass range
to .Comment: 5 pages, 3 figures. Appendix added with additional figures. Updated
to published versio
Why Developing Countries Should Adopt Intermediate Exchange Rate Regimes: Examining Brazil’s Experience
Multimessenger Universe with Gravitational Waves from Binaries
Future GW detector networks and EM observatories will provide a unique
opportunity to observe the most luminous events in the Universe involving
matter in extreme environs. They will address some of the key questions in
physics and astronomy: formation and evolution of compact binaries, sites of
formation of heavy elements and the physics of jets.Comment: 11 pages, two tables, White Paper submitted to the Astro-2020 (2020
Astronomy and Astrophysics Decadal Survey) by GWIC-3G Science Case Team
(GWIC: Gravitational-Wave International Committee
Measuring the nuclear equation of state with neutron star-black hole mergers
Gravitational-wave (GW) observations of neutron star-black hole (NSBH)
mergers are sensitive to the nuclear equation of state (EOS). Using realistic
simulations of NSBH mergers, incorporating both GW and electromagnetic (EM)
selection to ensure sample purity, we find that a GW detector network operating
at O5-sensitivities will constrain the radius of a NS and the
maximum NS mass with and precision, respectively. The results
demonstrate strong potential for insights into the nuclear EOS, provided NSBH
systems are robustly identified.Comment: 9 pages, 4 Figures. Submitted. Comments welcome
Gravitational radiation reaction in the equations of motion of compact binaries to 3.5 post-Newtonian order
We compute the radiation reaction force on the orbital motion of compact
binaries to the 3.5 post-Newtonian (3.5PN) approximation, i.e. one PN order
beyond the dominant effect. The method is based on a direct PN iteration of the
near-zone metric and equations of motion of an extended isolated system, using
appropriate ``asymptotically matched'' flat-space-time retarded potentials. The
formalism is subsequently applied to binary systems of point particles, with
the help of the Hadamard self-field regularisation. Our result is the 3.5PN
acceleration term in a general harmonic coordinate frame. Restricting the
expression to the centre-of-mass frame, we find perfect agreement with the
result derived in a class of coordinate systems by Iyer and Will using the
energy and angular momentum balance equations.Comment: 28 pages, references added, to appear in Classical and Quantum
Gravit
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