1,828 research outputs found
"Kludge" gravitational waveforms for a test-body orbiting a Kerr black hole
One of the most exciting potential sources of gravitational waves for
low-frequency, space-based gravitational wave (GW) detectors such as the
proposed Laser Interferometer Space Antenna (LISA) is the inspiral of compact
objects into massive black holes in the centers of galaxies. The detection of
waves from such "extreme mass ratio inspiral" systems (EMRIs) and extraction of
information from those waves require template waveforms. The systems' extreme
mass ratio means that their waveforms can be determined accurately using black
hole perturbation theory. Such calculations are computationally very expensive.
There is a pressing need for families of approximate waveforms that may be
generated cheaply and quickly but which still capture the main features of true
waveforms. In this paper, we introduce a family of such "kludge" waveforms and
describe ways to generate them. We assess performance of the introduced
approximations by comparing "kludge" waveforms to accurate waveforms obtained
by solving the Teukolsky equation in the adiabatic limit (neglecting GW
backreaction). We find that the kludge waveforms do extremely well at
approximating the true gravitational waveform, having overlaps with the
Teukolsky waveforms of 95% or higher over most of the parameter space for which
comparisons can currently be made. Indeed, we find these kludges to be of such
high quality (despite their ease of calculation) that it is possible they may
play some role in the final search of LISA data for EMRIs.Comment: 29 pages, 11 figures, requires subeqnarray; v2 contains minor changes
for consistency with published versio
The Current Status of Binary Black Hole Simulations in Numerical Relativity
Since the breakthroughs in 2005 which have led to long term stable solutions
of the binary black hole problem in numerical relativity, much progress has
been made. I present here a short summary of the state of the field, including
the capabilities of numerical relativity codes, recent physical results
obtained from simulations, and improvements to the methods used to evolve and
analyse binary black hole spacetimes.Comment: 14 pages; minor changes and corrections in response to referee
Intermediate and extreme mass-ratio inspirals — astrophysics, science applications and detection using LISA
Black hole binaries with extreme (gtrsim104:1) or intermediate (~102–104:1) mass ratios are among the most interesting gravitational wave sources that are expected to be detected by the proposed laser interferometer space antenna (LISA). These sources have the potential to tell us much about astrophysics, but are also of unique importance for testing aspects of the general theory of relativity in the strong field regime. Here we discuss these sources from the perspectives of astrophysics, data analysis and applications to testing general relativity, providing both a description of the current state of knowledge and an outline of some of the outstanding questions that still need to be addressed. This review grew out of discussions at a workshop in September 2006 hosted by the Albert Einstein Institute in Golm, Germany
Ground-based CCD astrometry with wide field imagers. III. [email protected] proper-motion catalog of the globular cluster omega Centauri
Omega Centauri is the most well studied Globular Cluster because of its
numerous puzzling features. Intensive spectroscopic follow-up observing
campaigns targeting stars at different positions on the color-magnitude diagram
promises to clarify some of these peculiarities. To able to target cluster
members reliably during spectroscopic surveys and both spatial and radial
distributions in the cluster outskirts without including field stars, a high
quality proper-motion catalog of omega Cen and membership probability
determination are required. The only available wide field proper-motion catalog
of omega Cen is derived from photographic plates, and only for stars brighter
than B~16. Using ESO archive data, we create a new, CCD-based, proper-motion
catalog for this cluster, extending to B~20. We used the high precision
astrometric software developed specifically for data acquired by [email protected]
telescope and presented in the first paper of this series. We achieved a good
cluster-field separation with a temporal base-line of only four years. We
corrected our photometry for sky-concentration effects. We provide calibrated
photometry for UBVRI wide-band data plus narrow-band filter data centered on
H_alpha for almost 360 000 stars. We can confirm that the omega Cen metal-poor
and the metal-rich components have the same proper motion, and demonstrate that
the metal-intermediate component in addition exhibits the same mean motion as
the other RGB stars. We provided membership probability determination for
published omega Cen variable star catalogs. Our catalog extends the
proper-motion measurements to fainter than the cluster turn-off luminosity, and
covers a wide area (~33'x33') around the center of omega Cen. Our catalog is
now electronically available to the astronomical community.Comment: 21 pages, 15 figures (8 in low resolution), shortened abstract,
revised version, accepted (October 3rd, 2008) for publication in A&
The Formation of the First Massive Black Holes
Supermassive black holes (SMBHs) are common in local galactic nuclei, and
SMBHs as massive as several billion solar masses already exist at redshift z=6.
These earliest SMBHs may grow by the combination of radiation-pressure-limited
accretion and mergers of stellar-mass seed BHs, left behind by the first
generation of metal-free stars, or may be formed by more rapid direct collapse
of gas in rare special environments where dense gas can accumulate without
first fragmenting into stars. This chapter offers a review of these two
competing scenarios, as well as some more exotic alternative ideas. It also
briefly discusses how the different models may be distinguished in the future
by observations with JWST, (e)LISA and other instruments.Comment: 47 pages with 306 references; this review is a chapter in "The First
Galaxies - Theoretical Predictions and Observational Clues", Springer
Astrophysics and Space Science Library, Eds. T. Wiklind, V. Bromm & B.
Mobasher, in pres
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
Bostonia: The Boston University Alumni Magazine. Volume 18
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
The Search for Gravitational Waves
Experiments aimed at searching for gravitational waves from astrophysical
sources have been under development for the last 40 years, but only now are
sensitivities reaching the level where there is a real possibility of
detections being made within the next five years. In this article a history of
detector development will be followed by a description of current detectors
such as LIGO, VIRGO, GEO 600, TAMA 300, Nautilus and Auriga. Preliminary
results from these detectors will be discussed and related to predicted
detection rates for some types of sources. Experimental challenges for detector
design are introduced and discussed in the context of detector developments for
the future.Comment: 21 pages, 7 figures, accepted J. Phys. B: At. Mol. Opt. Phy
Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector
The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30
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