9,231 research outputs found
(Sort of) Testing relativity with extreme mass ratio inspirals
The inspirals of ``small'' () compact bodies through highly
relativistic orbits of massive (several several ) black holes are among the most anticipated sources for the LISA
gravitational-wave antenna. The measurement of these waves is expected to map
the spacetime of the larger body with high precision, allowing us to test in
detail the hypothesis that black hole candidates are described by the Kerr
metric of general relativity. In this article, we will briefly describe how
these sources can be used to perform such a test. These proposed measurements
are often described as ``testing relativity''. This description is at best
somewhat glib: Because -- at least to date -- all work related to these
measurements assumes general relativity as the theoretical framework in which
these tests are performed, the measurements cannot be said to ``test
relativity'' in a fundamental way. More accurately, they test the {\it nature
of massive compact bodies within general relativity}. A surprising result for
such a test could point to deviations from general relativity, and would
provide an experimentally motivated direction in which to pursue tests of
gravity theories beyond GR.Comment: 8 pages, 2 figures, for the Proceedings of the Sixth International
LISA Symposiu
Gravitational wave astronomy and cosmology
The first direct observation of gravitational waves' action upon matter has
recently been reported by the BICEP2 experiment. Advanced ground-based
gravitational-wave detectors are being installed. They will soon be
commissioned, and then begin searches for high-frequency gravitational waves at
a sensitivity level that is widely expected to reach events involving compact
objects like stellar mass black holes and neutron stars. Pulsar timing arrays
continue to improve the bounds on gravitational waves at nanohertz frequencies,
and may detect a signal on roughly the same timescale as ground-based
detectors. The science case for space-based interferometers targeting
millihertz sources is very strong. The decade of gravitational-wave discovery
is poised to begin. In this writeup of a talk given at the 2013 TAUP
conference, we will briefly review the physics of gravitational waves and
gravitational-wave detectors, and then discuss the promise of these
measurements for making cosmological measurements in the near future.Comment: 11 pages. Proceedings writeup of a talk given at the 2013 Topics in
Astroparticle and Underground Physics (TAUP) conferenc
Gravitational waves from inspiral into massive black holes
Space-based gravitational-wave interferometers such as LISA will be sensitive
to the inspiral of stellar mass compact objects into black holes with masses in
the range of roughly 10^5 solar masses to (a few) 10^7 solar masses. During the
last year of inspiral, the compact body spends several hundred thousand orbits
spiraling from several Schwarzschild radii to the last stable orbit. The
gravitational waves emitted from these orbits probe the strong-field region of
the black hole spacetime and can make possible high precision tests and
measurements of the black hole's properties. Measuring such waves will require
a good theoretical understanding of the waves' properties, which in turn
requires a good understanding of strong-field radiation reaction and of
properties of the black hole's astrophysical environment which could complicate
waveform generation. In these proceedings, I review estimates of the rate at
which such inspirals occur in the universe, and discuss what is being done and
what must be done further in order to calculate the inspiral waveform.Comment: 7 pages, 2 figures. To appear in the proceedings of the 3rd Edoardo
Amaldi meetin
A brief survey of LISA sources and science
LISA is a planned space-based gravitational-wave (GW) detector that would be
sensitive to waves from low-frequency sources, in the band of roughly . This is expected to be an
extremely rich chunk of the GW spectrum -- observing these waves will provide a
unique view of dynamical processes in astrophysics. Here we give a quick survey
of some key LISA sources and what GWs can uniquely teach us about these
sources. Particularly noteworthy science which is highlighted here is the
potential for LISA to track the moderate to high redshift evolution of black
hole masses and spins through the measurement of GWs generated from massive
black hole binaries (which in turn form by the merger of galaxies and
protogalaxies). Measurement of these binary black hole waves has the potential
to determine the masses and spins of the constituent black holes with
percent-level accuracy or better, providing a unique high-precision probe of an
aspect of early structure growth. This article is based on the ``Astrophysics
Tutorial'' talk given by the author at the Sixth International LISA Symposium.Comment: 8 pages, 2 figures, for the Proceedings of the Sixth International
LISA Symposium. Particularly silly typo in one equation fixe
Probing strong-field gravity and black holes with gravitational waves
Gravitational wave observations will be excellent tools for making precise
measurements of processes that occur in very strong-field regions of spacetime.
Extreme mass ratio systems, formed by the capture of a stellar mass body
compact by a massive black hole, will be targets for planned space-based
interferometers such as LISA and DECIGO. These systems will be especially
powerful tools for testing the spacetime nature of black hole candidates. In
this writeup of the talk I gave at JGRG19, I describe how the properties of
black holes are imprinted on their waveforms, and how measurements can be used
to study these properties and thereby learn about the astrophysics of black
holes and about strong-field gravity.Comment: 19 pages, 5 figures, for the Proceedings of the 19th Workshop on
General Relativity and Gravitation in Japan. Content very similar to recent
reviews by the autho
Strong-field tidal distortions of rotating black holes: II. Horizon dynamics from eccentric and inclined orbits
In a previous paper, we developed tools for studying the horizon geometry of
a Kerr black hole that is tidally distorted by a binary companion using
techniques that require large mass ratios but can be applied to any bound orbit
and allow for arbitrary black hole spin. We now apply these tools to generic
Kerr black hole orbits. This allows us to investigate horizon dynamics: the
tidal field perturbing the horizon's geometry varies over a generic orbit, with
significant variations for eccentric orbits. Many of the features of the
horizon's behavior found previously carry over to the dynamical case in a
natural way. In particular, we find significant offsets between the applied
tide and the horizon's response. This leads to bulging in the horizon's
geometry which can lag or lead the orbit, depending upon the hole's rotation
and the orbit's geometry. An interesting and apparently new feature we find are
small-amplitude, high-frequency oscillations in the horizon's response. We have
not been able to identify a mechanism for producing these oscillations, but
find that they appear most clearly when rapidly rotating black holes are
distorted by very strong-field orbits.Comment: 24 pages, 15 figures. Final accepted version, to appear in Phys. Rev.
- …