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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

On the formation of black holes

The paper explores the consequences of the existence of a burning process beyond ordinary nuclear processes (which stop at iron), involving the 'strange' particles. In effect, this idea has already had considerable discussion within the high energy physics community in terms of 'quark' matter. A possible consequence is that neutron stars may explode rather than collapse to black holes. It should be evident that such a possibility suggests radically new scenarios for activity in galactic nuclei and gamma ray burst sources.

Michel, F. Curtis↗
NASA NTRS1986

The black hole binary A0620-00

CCD photometry obtained with the 1.3-m McGraw-Hill telescope during 1981-1985 and 490-560-nm spectra obtained at KPNO on Jan. 17, 1985, are reported for A0620-00. The mass of the compact X-ray source is found to have lower limit 3.20 solar mass, strongly implying that it is a black hole; its mass is shown to exceed 7.3 solar mass if the K dwarf fills its Roche lobe during quiescence.

Mcclintock, J. E.↗
NASA NTRS2012

On the Determination of the Spin of the Black Hole in Cyg X-1 from X-Ray Reflection Spectra

The spin of Cygnus X-I is measured by fitting reflection models to Suzaku data covering the energy band 0.9-400 keY. The inner radius of the accretion disc is found to lie within 2 gravitational radii (rg = GM/c(exp 2)) and a value for the dimensionless black hole spin is obtained of 0.97(sup .0.14) (sup -0.02). This agrees with recent measurements using the continuum fitting method by Gou et al. and of the broad iron line by Duro et al. The disc inclination is measured at 23.7(sup +6.7) (sup -5.4) deg. which is consistent with the recent optical measurement of the binary system inclination by Orosz et al of 27+/- 0.8 deg. We pay special attention to the emissivity profile caused by irradiation of the inner disc by the hard power-law source. 1be X-ray observations and simulations show that the index q of that profile deviates from the commonly used, Newtonian, value of 3 within 3r(sub g), steepening considerably within 2r(sub g). as expected in the strong gravity regime.

Fabian, A. C.↗
NASA NTRS1979

GX339-4 - A new black hole candidate

HEAO-1 observations of aperiodic variability in the galactic X-ray source GX339-4 (4U 1658-48) on time scales of tens of milliseconds to a few seconds are reported. It is shown that the overall characteristics of GX339-4 place it in the same class of X-ray sources as Cyg X-1 and Cir X-1, which are candidates for black holes in binary systems. The detection of X-ray flares from GX339-4 is discussed, particularly a series of five sequential flares with separations of about 250 ms.

Samimi, J.↗
NASA NTRS1972

Further evidence for a black hole in Beta Lyrae.

Comments regarding an interpretation of the OAO-2 observations of Beta Lyrae are presented. This interpretation had been reported by Wilson (1971). Six color UV curves represent the first continual coverage of a single cycle of Beta Lyr. Explanations for the deepening secondary minimum in the far UV are discussed. It is pointed out that the secondary component is apparently a massive object. The 'black hole' model represents one approach to interpret the observations of Beta Lyr.

Kondo, Y.↗
NASA NTRS1985

The natural angular momentum distribution in the study of thick disks around black holes

The thick-disk model is reviewed with an angular momentum distribution chosen to have a power-law relation with the von Zeipel parameter lambda = sq rt(l/Omega), where l denotes the specific angular momentum and Omega denotes the angular velocity. This choice permits the integration of the relativistic Euler equation independent of the background geometry. The consequences with regard to the Schwarzschild and Kerr black-hole geometries are briefly investigated.

Chakrabarti, S. K.↗
NASA NTRS2018

Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR

Nearby galaxy surveys have long classified X-ray binaries (XRBs) by the mass category of their donor stars (high-mass and low-mass). The NuSTAR (Nuclear Spectroscopic Telescope Array) observatory, which provides imaging data at E greater than 10 keV (kiloelectronvolts), has enabled the classification of extragalactic XRBs by their compact object type: neutron star (NS) or black hole (BH). We analyzed NuSTAR/Chandra/XMM-Newton observations from a NuSTAR-selected sample of 12 galaxies within 5 Mpc (megaparsecs) having stellar masses (M (sub asterisk)) 10 (sup 7-11) solar masses and star formation rates (SFRs) approximately 0.01-15 solar masses per year. We detected 128 NuSTAR sources to a sensitivity of 10 (sup 38) ergs per second. Using NuSTAR color-intensity and color-color diagrams we classified 43 of these sources as candidate NSs and 47 as candidate BHs. We further subdivide BHs by accretion states (soft, intermediate, and hard) and NSs by weak (Z/Atoll) and strong (accreting pulsar) magnetic field. Using eight normal (Milky Way-type) galaxies in the sample, we confirm the relation between the SFR and galaxy X-ray point source luminosity in the 4-25 and 12-25 keV energy bands. We also constrained galaxy X-ray point source luminosity using the relation L (sub X) equals M (sub asterisk) plus Beta SFR, finding agreement with previous work. The X-ray luminosity function (XLF) of all sources in the 4-25 and 12-25 keV energy bands matches the alpha = 1.6 slope for high-mass XRBs. We find that NS XLFs suggest a decline beginning at the Eddington limit for a 1.4 solar mass NS, whereas the BH fraction shows an approximate monotonic increase in the 4-25 and 12-25 keV energy bands. We calculate the overall ratio of BH to NS to be approximately 1 for 4-25 keV and approximately 2 for 12-25 keV.

Vulic, N.↗
NASA NTRS1996

Periodic outbursts from the black hole candidate 4U 1630-47

Observational data from several observatories, including Rosat, are used to identify two previously unreported outbursts from the ultrasoft X-ray transient 4U 1630-47. These outbursts occurred in March 1979 and September 1993, which is consistent with a previously reported 600-day outburst recurrence period. This source is a member of the class of transient X-ray binary systems that are thought to contain black holes. The 601.0 +/- 2.8 day period is the shortest observed so far for this class.

Parmar, A. N.↗
NASA NTRS1983

Visual slant misperception and the Black-Hole landing situation

A theory which explains the tendency for dangerously low approaches during night landing situations is presented. The two dimensional information at the pilot's eye contains sufficient information for the visual system to extract the angle of slant of the runway relative to the approach path. The analysis is depends upon perspective information which is available at a certain distance out from the aimpoint, to either side of the runway edgelights. Under black hole landing conditions, however, this information is not available, and it is proposed that the visual system use instead the only available information, the perspective gradient of the runway edgelights. An equation is developed which predicts the perceived approach angle when this incorrect parameter is used. The predictions are in close agreement with existing experimental data.

Perrone, J. A.↗
NASA NTRS1984

Visual slant misperception and the 'black-hole' landing situation

A theory which explains the tendency for dangerously low approaches during night landing situations is presented. The two-dimensional information at the pilot's eye contains sufficient information for the visual system to extract the angle of slant of the runway relative to the approach path. The analysis depends upon perspective information which is available at a certain distance out from the aimpoint, to either side of the runway edgelights. Under black hole landing conditions, however, this information is not available, and it is proposed that the visual system use instead the only available information, the perspective gradient of the runway edgelights. An equation is developed which predicts the perceived approach angle when this incorrect parameter is used. The predictions are in close agreement with existing experimental data.

Perrone, J. A.↗
NASA NTRS1989

Gamma-ray evidence for a stellar-mass black hole near the Galactic center

An analysis of the time variability of the observed 511-keV line emission from the direction of the Galactic center and the correlation of its variations in the continuum emission above 511 keV from the same direction suggest the existence of a compact object at or near the Galactic center. A possible mechanism of the observed positron annihilation is consistent with a compact interaction region of the order of 10 to the 8th cm. A black hole of several hundred solar masses is favored as a candidate for this compact object; arguments in support of this suggestion are presented.

Ramaty, Reuven↗
NASA NTRS2002

Tracking the moving optical photocenters of active galaxies: binary black holes, accretion disks and relativistic jets

We will use the astrometric capabilities of the Space Interferometry Mission to answer three key questions about active galactic nuclei: 1) Does the separation of the radio core and optical photocenter of quasars change on the same timescale as their photometric variability? 2) Does the most compact optical emission from an active galactic nucleus come from an accretion disk or from a relativistic jet? and 3) Do the cores of galaxies harbor binary supermassive black holes remaining from galaxy mergers?

astrometry↗
NASA NTRS1979

The Penrose photoproduction scenario for NGC 4151: A black hole gamma-ray emission mechanism for active galactic nuclei and Seyfert galaxies

A consistent theoretical interpretation is given for the suggestion that a steepening of the spectrum between X-ray and gamma ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. In the case of NGC 4151, the dominant process is shown to be Penrose Compton scattering in the ergosphere of a Kerr black hole, assumed to exist in the Seyfert's active galactic nucleus.

Leiter, D.↗
NASA NTRS2003

Long-Term Spectral and Timing Behavior of Black Hole Candidate XTE J1908+094

The X-ray transient XTE J1908+094 was serendipitously discovered during RXTE ToO observations of SGR 1900+14 in February 2002. Following the discovery, RXTE routinely monitored the region. At the onset, the source was found in a spectrally low/hard state lasting for approximately 40 days, followed by a quick transition to the highhoft state. At the highest X-ray intensity level (seen on 2002 April 6), the source flux (2-10 keV) reached approximately 105 mCrab, then decayed rapidly. Overall outburst characteristics resemble the transient behavior of galactic black hole candidates. Here, we present the long term light curves, and detailed spectral and timing investigations of XTE J1098+094 using the RXTE/PCA data. We also report the results of Chandra ACIS observations which were performed during the decay phase.

Gogus, E.↗
NASA NTRS1994

Soft gamma-ray repeaters: Black holes in giant molecular clouds?

The BATSE discovery of the near-simultaneous turnon of a soft gamma-ray repeater (SGR) source, located to apporximately 5 deg and possibly SGR 1900+14, and a new hard X-ray transient GRS 1915+105 (discovered by Granat), suggests they may be associated. Published positions for both the SGR and GRS sources do not preclude spatial coincidence for the two sources, or the GRS transient may be associated with another SGR source. We outline a model for SGR sources as due to thermal instabilities in spherical accretion onto black holes in giant molecular clouds. We show that the SIGMA position for the GRS 1915 source is consistent with it being in a giant molecular cloud and compare this possible identification with that suggested for the `1E' source in the Galactic center region. Our model would predict a strong concentration of SGR sources toward the Galactic plane (consistent with both SGR 1900+14 and SGR 1806-20) and so would require the only other known 'SGR,' the GRB 790305 superburst source apparently in the Large Magellanic Cloud, to be fundamentally different. We note that the recently discovered radio/infrared counterpart for the SGR 1806-20 may be consistent with this model, rather than the compact suprernova remnant/pulsar model suggested by Kulkarni and Frail.

Grindlay, Jonathan E.↗
NASA NTRS2007

Advances in Black-Hole Mergers: Spins and Unequal Masses

The last two years have seen incredible development in numerical relativity: from fractions of an orbit, evolutions of an equal-mass binary have reached multiple orbits, and convergent gravitational waveforms have been produced from several research groups and numerical codes. We are now able to move our attention from pure numerics to astrophysics, and address scenarios relevant to current and future gravitational-wave detectors.Over the last 12 months at NASA Goddard, we have extended the accuracy of our Hahn-Dol code, and used it to move toward these goals. We have achieved high-accuracy simulations of black-hole binaries of low initial eccentricity, with enough orbits of inspiral before merger to allow us to produce hybrid waveforms that reflect accurately the entire lifetime of the BH binary. We are extending this work, looking at the effects of unequal masses and spins.

Kelly, Bernard↗
NASA NTRS2002

Using Multiwavelength Observations to Determine the Black Hole Mass and Accretion Rate in the Type 1 Seyfert Galaxy NGC 5548

We model the spectral energy distribution of the type 1 Seyfert galaxy NGC 5548, fitting data from simultaneous optical, UV, and X-ray monitoring observations. We assume a geometry consisting of a hot central Comptonizing region surrounded by a thin accretion disk. The properties of the disk and the hot central region are determined by the feedback occurring between the hot Comptonizing region and thermal reprocessing in the disk that, along with viscous dissipation, provides the seed photons for the Comptonization process. The constraints imposed upon this model by the multiwavelength data allow us to derive limits on the central black hole mass, Mu is approximately or less than 2x10(exp 7) solar mass, the accretion rate, Mu is approximately or less than 2.5x10(exp 5) sq solar mass per year/Mu, and the radius of the transition region between the thin outer disk and the geometrically thick, hot inner region, is approximately 2-5x10(exp 14) cm.

Chiang, James↗