197 research outputs found
Long-Term Evolution of Massive Black Hole Binaries. III. Binary Evolution in Collisional Nuclei
[Abridged] In galactic nuclei with sufficiently short relaxation times,
binary supermassive black holes can evolve beyond their stalling radii via
continued interaction with stars. We study this "collisional" evolutionary
regime using both fully self-consistent N-body integrations and approximate
Fokker-Planck models. The N-body integrations employ particle numbers up to
0.26M and a direct-summation potential solver; close interactions involving the
binary are treated using a new implementation of the Mikkola-Aarseth chain
regularization algorithm. Even at these large values of N, two-body scattering
occurs at high enough rates in the simulations that they can not be simply
scaled to the large-N regime of real galaxies. The Fokker-Planck model is used
to bridge this gap; it includes, for the first time, binary-induced changes in
the stellar density and potential. The Fokker-Planck model is shown to
accurately reproduce the results of the N-body integrations, and is then
extended to the much larger N regime of real galaxies. Analytic expressions are
derived that accurately reproduce the time dependence of the binary semi-major
axis as predicted by the Fokker-Planck model. Gravitational wave coalescence is
shown to occur in <10 Gyr in nuclei with velocity dispersions below about 80
km/s. Formation of a core results from a competition between ejection of stars
by the binary and re-supply of depleted orbits via two-body scattering. Mass
deficits as large as ~4 times the binary mass are produced before coalescence.
After the two black holes coalesce, a Bahcall-Wolf cusp appears around the
single hole in one relaxation time, resulting in a nuclear density profile
consisting of a flat core with an inner, compact cluster, similar to what is
observed at the centers of low-luminosity spheroids.Comment: 21 page
Massive perturbers and the efficient merger of binary massive black holes
We show that dynamical relaxation in the aftermath of a galactic merger and
the ensuing formation and decay of a binary massive black hole (MBH), are
dominated by massive perturbers (MPs) such as giant molecular clouds or
clusters. MPs accelerate relaxation by orders of magnitude relative to 2-body
stellar relaxation alone, and efficiently scatter stars into the binary MBH's
orbit. The 3-body star-binary MBH interactions shrink the binary MBH to the
point where energy losses from the emission of gravitational waves (GW) lead to
rapid coalescence. We model this process based on observed and simulated MP
distributions and take into account the decreased efficiency of the star-binary
MBH interaction due to acceleration in the galactic potential. We show that
mergers of gas-rich galactic nuclei lead to binary MBH coalescence well within
the Hubble time. Moreover, lower-mass binary MBHs (<10^8 Msun) require only a
few percent of the typical gas mass in a post-merger nucleus to coalesce in a
Hubble time. The fate of a binary MBH in a gas poor galactic merger is less
certain, although massive stellar structures (e.g. clusters, stellar rings)
could likewise lead to efficient coalescence. These coalescence events are
observable by their strong GW emission. MPs thus increase the cosmic rate of
such GW events, lead to a higher mass deficit in the merged galactic core and
suppress the formation of triple MBH systems and the resulting ejection of MBHs
into intergalactic space.Comment: 14 pages, 4 figures, 3 tables. More detailed explanations and changes
in structure. Section on hypervelocity stars moved to another paper (in
preparation). Results and conclusions unchanged. Accepted to Ap
Wavelength-dependent reflectivity changes on gold at elevated electronic temperatures
Upon the excitation by an ultrashort laser pulse the conditions in a material
can drastically change, altering its optical properties and therefore the
relative amount of absorbed energy, a quan- tity relevant for determining the
damage threshold and for developing a detailed simulation of a structuring
process. The subject of interest in this work is the d-band metal gold which
has an absorption edge marking the transition of free valence electrons and an
absorbing deep d-band with bound electrons. Reflectivity changes are observed
in experiment over a broad spectral range at ablation conditions. To understand
the involved processes the laser excitation is modeled by a com- bination of
first principle calculations with a two-temperature model. The description is
kept most general and applied to realistically simulate the transfer of the
absorbed energy of a Gaussian laser pulse into the electronic system at every
point in space at every instance of time. An electronic temperature-dependent
reflectivity map is calculated, describing the out of equilibrium reflectivity
during laser excitation for photon energies from 0.9 - 6.4 eV, including inter-
and intra-band transi- tions and a temperature-dependent damping factor. The
main mechanisms are identified explaining the electronic temperature-dependent
change in reflectivity: broadening of the edge of the occu- pied/unoccupied
states around the chemical potential , also leading to a shift of the
and an increase of the collision rate of free s/p-band electrons with
bound d-band holes
Renormalized spin coefficients in the accumulated orbital phase for unequal mass black hole binaries
We analyze galactic black hole mergers and their emitted gravitational waves.
Such mergers have typically unequal masses with mass ratio of the order 1/10.
The emitted gravitational waves carry the inprint of spins and mass quadrupoles
of the binary components. Among these contributions, we consider here the
quasi-precessional evolution of the spins. A method of taking into account
these third post-Newtonian (3PN) effects by renormalizing (redefining) the 1.5
PN and 2PN accurate spin contributions to the accumulated orbital phase is
developed.Comment: 10 pages, to appear in Class. Quantum Grav. GWDAW13 Proceedings
Special Issue, v2: no typos conjectur
A Chandra Study of the Radio Galaxy NGC 326: Wings, Outburst History, and AGN Feedback
NGC 326 is one of the most prominent X- or Z-shaped radio galaxies
(XRGs/ZRGs) and has been the subject of several studies attempting to explain
its morphology through either fluid motions or reorientation of the jet axis.
We examine a 100 ks archival Chandra exposure and find several features
associated with the radio galaxy: a high-temperature front that may indicate a
shock, high-temperature knots around the rim of the radio emission, and a
cavity associated with the eastern wing of the radio galaxy. A reasonable
interpretation of these features in light of the radio data allows us to
reconstruct the history of the AGN outbursts. The active outburst was likely
once a powerful radio source which has since decayed, and circumstantial
evidence favors reorientation as the means to produce the wings. Because of the
obvious interaction between the radio galaxy and the ICM and the wide
separation between the active lobes and wings, we conclude that XRGs are
excellent sources in which to study AGN feedback in galaxy groups by measuring
the heating rates associated with both active and passive heating mechanisms.Comment: 13 pages, 8 figures, Accepted by Ap
Review: innovation through research in the North American pork industry
This article involved a broad search of applied sciences for milestone technologies we deem to be the most significant innovations applied by the North American pork industry, during the past 10 to 12 years. Several innovations shifted the trajectory of improvement or resolved significant production limitations. Each is being integrated into practice, with the exception being gene editing technology, which is undergoing the federal approval process. Advances in molecular genomics have been applied to gene editing for control of porcine reproductive and respiratory syndrome and to identify piglet genome contributions from each parent. Post-cervical artificial insemination technology is not novel, but this technology is now used extensively to accelerate the rate of genetic progress. A milestone was achieved with the discovery that dietary essential fatty acids, during lactation, were limiting reproduction. Their provision resulted in a dose-related response for pregnancy, pregnancy maintenance and litter size, especially in maturing sows and ultimately resolved seasonal infertility. The benefit of segregated early weaning (12 to 14 days of age) was realized for specific pathogen removal for genetic nucleus and multiplication. Application was premature for commercial practice, as piglet mortality and morbidity increased. Early weaning impairs intestinal barrier and mucosal innate immune development, which coincides with diminished resilience to pathogens and viability later in life. Two important milestones were achieved to improve precision nutrition for growing pigs. The first involved the updated publication of the National Research Council nutrient requirements for pigs, a collaboration between scientists from America and Canada. Precision nutrition advanced further when ingredient description, for metabolically available amino acids and net energy (by source plant), became a private sector nutrition product. The past decade also led to fortuitous discoveries of health-improving components in ingredients (xylanase, soybeans). Finally, two technologies converged to facilitate timely detection of multiple pathogens in a population: oral fluids sampling and polymerase chain reaction (PCR) for pathogen analysis. Most critical diseases in North America are now routinely monitored by oral fluid sampling and prepared for analysis using PCR methods
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