1,247 research outputs found
The effect of gravitational-wave recoil on the demography of massive black holes
The coalescence of massive black hole (MBH) binaries following galaxy mergers
is one of the main sources of low-frequency gravitational radiation. A
higher-order relativistic phenomenon, the recoil as a result of the non-zero
net linear momentum carried away by gravitational waves, may have interesting
consequences for the demography of MBHs at the centers of galaxies. We study
the dynamics of recoiling MBHs and its observational consequences. The
``gravitational rocket'' may: i) deplete MBHs from late-type spirals, dwarf
galaxies, and stellar clusters; ii) produce off-nuclear quasars, including
unusual radio morphologies during the recoil of a radio-loud source; and iii)
give rise to a population of interstellar and intergalactic MBHs.Comment: emulateapj, 5 pages, 2 figures, to appear in the ApJ Letter
Optical Coronagraphic Spectroscopy of AU Mic: Evidence of Time Variable Colors?
We present coronagraphic long slit spectra of AU Mic's debris disk taken with
the STIS instrument aboard the Hubble Space Telescope (HST). Our spectra are
the first spatially resolved, scattered light spectra of the system's disk,
which we detect at projected distances between approximately 10 and 45 AU. Our
spectra cover a wavelength range between 5200 and 10200 angstroms. We find that
the color of AU Mic's debris disk is bluest at small (12-35 AU) projected
separations. These results both confirm and quantify the findings qualitatively
noted by Krist et al. (2005), and are different than IR observations that
suggested a uniform blue or gray color as a function of projected separation in
this region of the disk. Unlike previous literature that reported the color of
AU Mic's disk became increasingly more blue as a function of projected
separation beyond approximately 30 AU, we find the disk's optical color between
35-45 AU to be uniformly blue on the southeast side of the disk and
decreasingly blue on the northwest side. We note that this apparent change in
disk color at larger projected separations coincides with several fast, outward
moving "features" that are passing through this region of the southeast side of
the disk. We speculate that these phenomenon might be related, and that the
fast moving features could be changing the localized distribution of sub-micron
sized grains as they pass by, thereby reducing the blue color of the disk in
the process. We encourage follow-up optical spectroscopic observations of the
AU Mic to both confirm this result, and search for further modifications of the
disk color caused by additional fast moving features propagating through the
disk.Comment: Accepted by AJ, 13 pages, 8 figures, 1 tabl
Constraining the Accretion Rate Onto Sagittarius A* Using Linear Polarization
Two possible explanations for the low luminosity of the supermassive black
hole at the center of our galaxy are (1) an accretion rate of order the
canonical Bondi value (roughly 10^{-5} solar masses per year), but a very low
radiative efficiency for the accreting gas or (2) an accretion rate much less
than the Bondi rate. Both models can explain the broad-band spectrum of the
Galactic Center. We show that they can be distinguished using the linear
polarization of synchrotron radiation. Accretion at the Bondi rate predicts no
linear polarization at any frequency due to Faraday depolarization. Low
accretion rate models, on the other hand, have much lower gas densities and
magnetic field strengths close to the black hole; polarization may therefore be
observable at high frequencies. If confirmed, a recent detection of linear
polarization from Sgr A above 150 GHz argues for an accretion rate of order
10^{-8} solar masses per year, much less than the Bondi rate. This test can be
applied to other low-luminosity galactic nuclei.Comment: final version accepted by ApJ; references added, somewhat shortene
Cooperation in farm accounting
One year ago the Michigan State Grange entered into co-operation with the Michigan Agricultural College and the United States Department of Agriculture, in the matter of securing data on the costs of farming and income of farms. By this co-operation it was proposed to discover the types of farming that are paying best in Michigan, and to furnish data which farmers may use in changing their farm business to a basis of greater profits. Under this plan the Grange distributed 1,075 account books to their members. These account books contain two parts. One part is for crop records only, and it was intended that the crop records would be kept by farmers and furnished to the College in time to be summarized and presented to the State Grange at their meeting in December, 1920. The second part of the book was for a full year\u27s record and was to be completed and summarized at the end of the full twelve months. The following data is, therefore, a preliminary report upon the important crops of the State. It shows the yields and income from each crop, and it also shows the enterprise or special costs on each crop. The term, enterprise returns, means total yields in money less special costs. Figures on enterprise returns when used with proper consideration as to labor distribution will give a farmer the data necessary to determine the best paying combination of enterprises for his farm
On The Nature of the Variable Infrared Emission from Sgr A*
Recent infrared (IR) observations of the center of our Galaxy indicate that
the supermassive black hole source Sgr A* is strongly variable in the IR. The
timescale for the variability, min, is comparable to that of the
X-ray flares observed by {\em Chandra} and {\em XMM}, suggesting a common
physical origin. In this paper, we investigate the nature of the IR emission in
the context of models recently proposed to interpret the X-ray flares. We show
that the IR emission in Sgr A* can be well explained by nonthermal synchrotron
emission if a small fraction of the electrons in the innermost region of the
accretion flow around the black hole are accelerated {into a broken power-law
distribution}, perhaps due to transient events such as magnetic reconnection.
The model predicts differences in the variability amplitudes of flares in the
IR and X-rays, in general agreement with observations. It also predicts that
the IR emission should be linearly polarized, as has indeed been observed
during one epoch. IR and X-ray flares analogous to those observed in Sgr A* may
be detectable from other accreting SMBHs, provided L \lsim 10^{-8} L_{EDD};
at higher luminosities the flaring emission is dominated by thermal
synchrotron-self Compton emission, which is likely to be less variable.Comment: 17 pages, 5 figures, accepted by Ap
Physician–Patient Communication About Sexual Functioning in Patients with Multiple Sclerosis
Sexual dysfunction is quite common among individuals with multiple sclerosis (MS); however, severity of dysfunction alone does not account for the tremendous variation in sexual satisfaction across individuals living with MS. Individual characteristics, relationships with intimate partners, and environmental factors all likely contribute to the multidimensional experience of sexual satisfaction. Health care provider variables, including how one communicates with providers about sexual concerns, may also be influential. The purpose of this study was to examine factors that are associated with patients’ sex-related communications with their MS physicians and to overall patient sexual satisfaction. Individuals in an MS clinic (n = 73) completed a survey packet which included measures of physical and mental health, sexual dysfunction, sexual satisfaction, sex communication, health care provider relationships, and health care satisfaction. Findings suggest that while more than half of patients with MS reported experiencing sexual dysfunction, only a third of patients indicated addressing their sexual concerns with their physician during the past year. Interestingly, the frequency of communication about sexual concerns was associated with satisfaction with physician variables, whereas selfefficacy for these interactions was associated with emotional health variables. These results indicate that when considering interventions to increase confidence for communication and frequency of communication that differing factors may be taken into account
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