79 research outputs found
Merger of Black Holes in the Galactic Center
We present the results of three body simulations focused on understanding the
fates of intermediate mass black holes (IBH) that drift within the central 0.5
pc of the Galaxy. In particular, we modeled the interactions between pairs of
black holes as they orbit a central blac k hole of mass
. The simulations performed assume a
Schwarzschild geometry and account for Chandrasekhar dynamical friction as well
as acceleration resulting from energy lost due to gravitational radiation.
We found the branching ratio for one of the orbiting IBHs to merge with the
CBH was 0.95 and is independent of the inner IBH's initial eccentricity as well
as the rate of sinking. This, coupled with an infall rate of yrs
for an IBH to drift into the Galactic center, results in an IBH-CBH merger
every Myrs. Lastly we found that the IBH-IBH-CBH triple body
system ``resets'' itself, in the sense that a system with an inner I BH with an
initially circular orbit generally left behind an IBH with a large
eccentricity, whereas a system in which the inner IBH had a high eccentricity
() usually left a remnant with low eccentricity. Branching ratios
for different outcomes are also similar in the two cases.Comment: Official paper to appear in November 2008 issue of Ap
The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
We describe the contents and functionality of the NASA Exoplanet Archive, a
database and tool set funded by NASA to support astronomers in the exoplanet
community. The current content of the database includes interactive tables
containing properties of all published exoplanets, Kepler planet candidates,
threshold-crossing events, data validation reports and target stellar
parameters, light curves from the Kepler and CoRoT missions and from several
ground-based surveys, and spectra and radial velocity measurements from the
literature. Tools provided to work with these data include a transit ephemeris
predictor, both for single planets and for observing locations, light curve
viewing and normalization utilities, and a periodogram and phased light curve
service. The archive can be accessed at
http://exoplanetarchive.ipac.caltech.edu.Comment: Accepted for publication in the Publications of the Astronomical
Society of the Pacific, 4 figure
Magneto-acoustic Waves in a Magnetic Slab Embedded in an Asymmetric Magnetic Environment: The Effects of Asymmetry
Modeling the behavior of magnetohydrodynamic waves in a range of magnetic geometries mimicking solar
atmospheric waveguides, from photospheric flux tubes to coronal loops, can offer a valuable contribution to the
field of solar magneto-seismology. The present study uses an analytical approach to derive the dispersion relation
for magneto-acoustic waves in a magnetic slab of homogeneous plasma enclosed on its two sides by semi-infinite
plasma of different densities, temperatures, and magnetic field strengths, providing an asymmetric plasma
environment. This is a step further in the generalization of the classic magnetic slab model, which is symmetric
about the slab, was developed by Roberts, and is an extension of the work by Allcock & Erdélyi where a magnetic
slab is sandwiched in an asymmetric nonmagnetic plasma environment. In contrast to the symmetric case, the
dispersion relation governing the asymmetric slab cannot be factorized into separate sausage and kink eigenmodes.
The solutions obtained resemble these well-known modes; however, their properties are now mixed. Therefore we
call these modes quasi-sausage and quasi-kink modes. If conditions on the two sides of the slab do not differ
strongly, then a factorization of the dispersion relation can be achieved for the further analytic study of various
limiting cases representing a solar environment. In the current paper, we examine the incompressible limit in detail
and demonstrate its possible application to photospheric magnetic bright points. After the introduction of a
mechanical analogy, we reveal a relationship between the external plasma and magnetic parameters, which allows
for the existence of quasi-symmetric modes
The status of GEO 600
The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode
Status of the GEO600 gravitational wave detector
The GEO600 laser interferometric gravitational wave detector is approaching the end of its commissioning phase which started in 1995.During a test run in January 2002 the detector was operated for 15 days in a power-recycled michelson configuration. The detector and environmental data which were acquired during this test run were used to test the data analysis code. This paper describes the subsystems of GEO600, the status of the detector by August 2002 and the plans towards the first science run
Search for gravitational waves from binary black hole inspirals in LIGO data
We report on a search for gravitational waves from binary black hole inspirals in the data from the second science run of the LIGO interferometers. The search focused on binary systems with component masses between 3 and 20M. Optimally oriented binaries with distances up to 1 Mpc could be detected with efficiency of at least 90%. We found no events that could be identified as gravitational waves in the 385.6 hours of data that we searched. © 2006 The American Physical Society
The ligo gravitational wave observatories: Recent results and future plans
The LIGO interferometers are operating as gravitational wave observatories, with a noise level near an order of magnitude of the goal and the first scientific data recently taken. This data has been analyzed for four different categories of gravitational wave sources; millisecond bursts, inspiralling binary neutron stars, periodic waves from a known pulsar, and stochastic background. Research and development is also underway for the next generation LIGO detector, Advanced LIGO
Joint LIGO and TAMA300 search for gravitational waves from inspiralling neutron star binaries
We search for coincident gravitational wave signals from inspiralling neutron star binaries using LIGO and TAMA300 data taken during early 2003. Using a simple trigger exchange method, we perform an intercollaboration coincidence search during times when TAMA300 and only one of the LIGO sites were operational. We find no evidence of any gravitational wave signals. We place an observational upper limit on the rate of binary neutron star coalescence with component masses between 1 and 3M of 49 per year per Milky Way equivalent galaxy at a 90% confidence level. The methods developed during this search will find application in future network inspiral analyses. © 2006 The American Physical Society
Evidence for Warped Disks of Young Stars in the Galactic Center
The central parsec around the super-massive black hole in the Galactic Center
hosts more than 100 young and massive stars. Outside the central cusp (R~1")
the majority of these O and Wolf-Rayet (WR) stars reside in a main clockwise
system, plus a second, less prominent disk or streamer system at large angles
with respect to the main system. Here we present the results from new
observations of the Galactic Center with the AO-assisted near-infrared imager
NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include
the detection of 27 new reliably measured WR/O stars in the central 12" and
improved measurements of 63 previously detected stars, with proper motion
uncertainties reduced by a factor of four compared to our earlier work. We
develop a detailed statistical analysis of their orbital properties and
orientations. Half of the WR/O stars are compatible with being members of a
clockwise rotating system. The rotation axis of this system shows a strong
transition as a function of the projected distance from SgrA*. The main
clockwise system either is either a strongly warped single disk with a
thickness of about 10 degrees, or consists of a series of streamers with
significant radial variation in their orbital planes. 11 out of 61 clockwise
moving stars have an angular separation of more than 30 degrees from the
clockwise system. The mean eccentricity of the clockwise system is 0.36+/-0.06.
The distribution of the counter-clockwise WR/O star is not isotropic at the 98%
confidence level. It is compatible with a coherent structure such as stellar
filaments, streams, small clusters or possibly a disk in a dissolving state.
The observed disk warp and the steep surface density distribution favor in situ
star formation in gaseous accretion disks as the origin of the young stars.Comment: ApJ in pres
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