11 research outputs found
Rotating black hole orbit functionals in the frequency domain
In many astrophysical problems, it is important to understand the behavior of
functions that come from rotating (Kerr) black hole orbits. It can be
particularly useful to work with the frequency domain representation of those
functions, in order to bring out their harmonic dependence upon the fundamental
orbital frequencies of Kerr black holes. Although, as has recently been shown
by W. Schmidt, such a frequency domain representation must exist, the coupled
nature of a black hole orbit's and motions makes it difficult to
construct such a representation in practice. Combining Schmidt's description
with a clever choice of timelike coordinate suggested by Y. Mino, we have
developed a simple procedure that sidesteps this difficulty. One first Fourier
expands all quantities using Mino's time coordinate . In particular,
the observer's time is decomposed with . The frequency domain
description is then built from the -Fourier expansion and the
expansion of . We have found this procedure to be quite simple to implement,
and to be applicable to a wide class of functionals. We test the procedure
using a simple test function, and then apply it in a particularly interesting
case, the Weyl curvature scalar used in black hole perturbation
theory.Comment: 16 pages, 2 figures. Submitted to Phys Rev D. New version gives a
vastly improved algorithm due to Drasco for computing the Fourier transforms.
Drasco has been added as an author. Also fixed some references and
exterminated a small herd of typos; final published versio
Enigma of ultraluminous X-ray sources may be resolved by 3D-spectroscopy (MPFS data)
The ultraluminous X-ray sources (ULXs) were isolated in external galaxies for
the last 5 years. Their X-ray luminosities exceed 100-10000 times those of
brightest Milky Way black hole binaries and they are extremely variable. There
are two models for the ULXs, the best black hole candidates. 1. They are
supercritical accretion disks around a stellar mass black hole like that in
SS433, observed close to the disk axes. 2. They are Intermediate Mass Black
Holes (of 100-10000 solar masses). Critical observations which may throw light
upon the ULXs nature come from observations of nebulae around the ULXs. We
present results of 3D-spectroscopy of nebulae around several ULXs located in
galaxies at 3-6 Mpc distances. We found that the nebulae to be powered by their
central black holes. The nebulae are shocked and dynamically perturbed probably
by jets. The nebulae are compared with SS433 nebula (W50).Comment: Proceedings of the ESO and Euro3D Workshop "Science Perspectives for
3D Spectroscopy", Garching (Germany), October 10-14, 2005. M. Kissler-Patig,
M.M. Roth and J.R. Walsh (eds.
Extrapolating SMBH correlations down the mass scale: the case for IMBHs in globular clusters
Empirical evidence for both stellar mass black holes M_bh<10^2 M_sun) and
supermassive black holes (SMBHs, M_bh>10^5 M_sun) is well established.
Moreover, every galaxy with a bulge appears to host a SMBH, whose mass is
correlated with the bulge mass, and even more strongly with the central stellar
velocity dispersion sigma_c, the `M-sigma' relation. On the other hand,
evidence for "intermediate-mass" black holes (IMBHs, with masses in the range
1^2 - 10^5 M_sun) is relatively sparse, with only a few mass measurements
reported in globular clusters (GCs), dwarf galaxies and low-mass AGNs. We
explore the question of whether globular clusters extend the M-sigma
relationship for galaxies to lower black hole masses and find that available
data for globular clusters are consistent with the extrapolation of this
relationship. We use this extrapolated M-sigma relationship to predict the
putative black hole masses of those globular clusters where existence of
central IMBH was proposed. We discuss how globular clusters can be used as a
constraint on theories making specific predictions for the low-mass end of the
M-sigma relation.Comment: 14 pages, 3 figures, accepted for publication in Astrophysics and
Space Science; fixed typos and a quote in Sec.
Stellar dynamics in young clusters: the formation of massive runaways and very massive runaway mergers
In the present paper we combine an N-body code that simulates the dynamics of
young dense stellar systems with a massive star evolution handler that accounts
in a realistic way for the effects of stellar wind mass loss. We discuss two
topics:
1. The formation and the evolution of very massive stars (with a mass >120
Mo) is followed in detail. These very massive stars are formed in the cluster
core as a consequence of the successive (physical) collison of 10-20 most
massive stars of the cluster (the process is known as runaway merging). The
further evolution is governed by stellar wind mass loss during core hydrogen
burning and during core helium burning (the WR phase of very massive stars).
Our simulations reveal that as a consequence of runaway merging in clusters
with solar and supersolar values, massive black holes can be formed but with a
maximum mass of 70 Mo. In small metallicity clusters however, it cannot be
excluded that the runaway merging process is responsible for pair instability
supernovae or for the formation of intermediate mass black holes with a mass of
several 100 Mo.
2. Massive runaways can be formed via the supernova explosion of one of the
components in a binary (the Blaauw scenario) or via dynamical interaction of a
single star and a binary or between two binaries in a star cluster. We explore
the possibility that the most massive runaways (e.g., zeta Pup, lambda Cep,
BD+433654) are the product of the collision and merger of 2 or 3 massive stars.Comment: Updated and final versio
Investigating the Nuclear Activity of Barred Spiral Galaxies: The Case of NGC 1672
We have performed an X-ray study of the nearby barred spiral galaxy NGC 1672, primarily to ascertain the effect of the bar on its nuclear activity. We use both Chandra and XMM-Newton observations to investigate its X-ray properties, together with supporting high-resolution optical imaging data from the Hubble Space Telescope (HST), infrared imaging from the Spitzer Space Telescope, and Australia Telescope Compact Array ground-based radio data.We detect 28 X-ray sources within the D25 area of the galaxy; many are spatially correlated with star formation in the bar and spiral arms, and two are identified as background galaxies in the HST images. Nine of the X-ray sources are ultraluminous X-ray sources, with the three brightest (LX > 5 × 1039 erg s−1) located at the ends of the bar. With the spatial resolution of Chandra, we are able to show for the first time that NGC 1672 possesses a hard (Γ ∼ 1.5) nuclear X-ray source with a 2–10 keV luminosity of 4 × 1038 erg s−1. This is surrounded by an X-ray-bright circumnuclear star-forming ring, comprised of point sources and hot gas, which dominates the 2–10 keV emission in the central region of the galaxy. The spatially resolved multiwavelength photometry indicates that the nuclear source is a low-luminosity active galactic nucleus (LLAGN), but with star formation activity close to the central black hole. A high-resolution multiwavelength survey is required to fully assess the impact of both large-scale bars and smaller-scale phenomena such as nuclear bars, rings, and nuclear spirals on the fueling of LLAGN
Host Plant Records for Fruit Flies (Diptera: Tephritidae: Dacini) in the Pacific Islands: 2. Infestation Statistics on Economic Hosts
Detailed host records are listed for 39 species of Bactrocera and 2 species of Dacus fruit flies, infesting 98 species of commercial and edible fruits in the Pacific Island Countries and Territories, based on sampling and incubating in laboratory almost 13,000 field collected samples, or over 380,000 fruits. For each host-fly-country association, quantitative data are presented on the weight and number of fruits collected, the proportion of infested samples, the number of adult flies emerged per kg of fruits and, whenever available, the percentage of individual fruits infested. All the published records of each fly-host-country association are cited and erroneous or dubious published records are rectified or commented. Laboratory forced infestation data are also cited and reviewed