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At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Preliminary risk assessment for the Black Brant XII

In order to provide the scientific community, as well as NASA management, with a preview of typical safety restrictions for the proposed Black Brant XII sounding rocket, a risk assessment for a typical payload has been performed. This paper details the considerations which ensure minimal risk for projects managed by Wallops Flight Facility and the safety criteria required to conduct an operation. Specifically, three launch scenarios for the Black Brant XII have been considered. The first case assumes a test launch from Wallops, and the other two cases analyze typical scientific missions from Poker Flat Research Range.

Underwood, B. E.↗
NASA NTRS1987

A simplified derivation of stimulated emission by black holes

A black hole, when acting as a scatterer for quanta in a single mode of a massless scalar field, is known to convert any ingoing Gibbs state of that mode into an outgoing Gibbs state (with some other mean particle number). The paper presents a simple derivation for this property which may help to clarify what relation, if any, it bears to the microscopic structure of the black hole horizon.

Sorkin, Rafael D.↗
NASA NTRS1986

Nucleosynthesis in the neighborhood of a black hole

The preliminary results from simulations of nucleosynthesis inside a thick accretion disk around a black hole are discussed as a function of the accretion rate, the viscosity parameter, and the mass of the black hole. Results for the Bondi accretion case are also presented. Taking the case of a 10-solar mass and a 10 to the 6th-solar mass central Schwarzschild hole, detailed evolution of a representative element of matter as it accretes into the hole is presented in the case when the initial abundance (at the outer edge of the disk) is the same as the solar abundance. It is suggested that such studies may eventually shed light on the composition of the outgoing jets observed in the active galaxies and SS433.

Chakrabarti, Sandip K.↗
NASA NTRS1988

Spectral evolution in black hole accretion powered AGN and the cosmic X-ray background

If AGN contain supermassive black holes of pregalactic origin, then the radiation emitted during their lifetime will undergo spectral evolution. For AGN black-hole-accretion disk dynamo power sources, the dynamic parameters relevant to spectral evolution are the electron crossing time in the dynamo, the electron radiative loss time, the compactness parameter, and the photon-photon pair production optical depth. It is suggested that both spectral and luminosity evolution may be required to explain the evolutionary properties of AGN.

Leiter, D.↗
NASA NTRS1988

The central engine of quasars and AGNs - Scaling to solar mass black holes

The model of the previous paper (Ellison and Kazanas, hereafter EK) can be readily scaled to model systems with black holes 3-10 solar masses, such as those expected to exist in certain Galactic X-ray binaries. The model can account in a straightforward way for the bimodal behavior of Cyg X-1 and the other Galactic black hole candidates (White and Marshall 1984; White, et al., 1984). It is argued that the change in the spectrum with luminosity is due to the drastic increase of both the source compactness and luminosity with small changes in the accretion rate, and conversion of most of the energy into electron-positron pairs which render the source optically thick and modify its spectrum. It is also argued that similar effects may be observed in AGNs.

Kazanas, D.↗
NASA NTRS1988

A test of the massive binary black hole hypothesis - Arp 102B

The emission-line spectra of several AGN have broad peaks which are significantly displaced in velocity with respect to the host galaxy. An interpretation of this effect in terms of orbital motion of a binary black hole predicts periods of a few centuries. It is pointed out here that recent measurements of the masses and sizes of many low-luminosity AGN imply orbital periods much shorter than this. In particular, it is found that the elliptical galaxy Arp 102B is the most likely candidate for observation of radial velocity variations; its period is expected to be about 3 yr. The H-alpha line profile of Arp 102B has been measured for 5 yr without detecting any change in velocity, and it is thus found that a rather restrictive observational test of the massive binary black hole hypothesis already exists, albeit for this one object.

Helpern, J. P.↗
NASA NTRS1988

Do massive black holes reside in elliptical galaxies?

The accretion by a central black hole of the hot interstellar medium in an elliptical galaxy is investigated, and the minimum expected luminosity and manner of its emission is estimated. It is not obviously detected at any wavelength. The problem of 'starving the monster', if indeed there is a monster, is raised. The simplest conclusion from the evidence is that most bright elliptical galaxies do not contain massive black holes.

Fabian, A. C.↗
NASA NTRS1989

Black light - How sensors filter spectral variation of the illuminant

Visual sensor responses may be used to classify objects on the basis of their surface reflectance functions. In a color image, the image data are represented as a vector of sensor responses at each point in the image. This vector depends both on the surface reflectance functions and on the spectral power distribution of the ambient illumination. Algorithms designed to classify objects on the basis of their surface reflectance functions typically attempt to overcome the dependence of the sensor responses on the illuminant by integrating sensor data collected from multiple surfaces. In machine vision applications, it is shown that it is often possible to design the sensor spectral responsivities so that the vector direction of the sensor responses does not depend upon the illuminant. The conditions under which this is possible are given and an illustrative calculation is performed. In biological systems, where the sensor responsivities are fixed, it is shown that some changes in the illumination cause no change in the sensor responses. Such changes in illuminant are called black illuminants. It is possible to express any illuminant as the sum of two unique components. One component is a black illuminant. The second component is called the visible component. The visible component of an illuminant completely characterizes the effect of the illuminant on the vector of sensor responses.

Brainard, David H.↗
NASA NTRS1989

The reflectance of Ames 24E, Infrablack, and Martin black

Results are reported from measurements of the specular reflectances (SRs) and bidirectional reflectance distribution functions (BRDFs) of three black optical coatings in the FIR wavelength range. The nonspecular reflectometer apparatus described by Smith (1984) is employed, and the data are presented in tables and graphs and discussed in detail. It is found that Ames 24E has an FIR SR one order of magnitude lower than that of Martin black (MB), with BRDF values characteristic of a nearly Lambertian surface, while Infrablack has SR two orders lower than MB and a specular-diffuse surface; MB itself has a very specular surface.

Smith, Sheldon M.↗
NASA NTRS1989

Disk-instability model for soft-X-ray transients containing black holes

Consideration is given to the time-dependent behavior of the accretion disks in low-mass X-ray binaries as a model for soft X-ray transients. The thermal stability and vertical structure properties of the disk are studied in the range between 10 to the 7th and 10 to the 8th cm. An Eulerian time-dependent thin disk model is used to show that, for relevant accretion rates, the disk suffers a thermal instability leading to intermittent accretion onto the central compact object. The disk instability model reproduces the basic features of outbursts of soft X-ray transients. Also, the physical state of quiescence of the binary A0620-00 is examined, focusing on the possible existence of a black hole. It is suggested that the modulation of the accretion flow in the inner disk may be responsible for the bimodal behavior observed in the spectra of black hole candidates such as Cyg X-1, GX 339-4, and A0620-00.

Mineshige, Shin↗
NASA NTRS1989

Active galactic nuclei. III - Accretion flow in an externally supplied cluster of black holes

This third paper in the series modeling QSOs and AGNs as clusters of accreting black holes studies the accretion flow within an externally supplied cluster. Significant radiation will be emitted by the cluster core, but the black holes in the outer halo, where the flow is considered spherically symmetric, will not contribute much to the overall luminosity of the source because of their large velocities relative to the infalling gas and therefore their small accretion radii. As a result, the scenario discussed in Paper I will refer to the cluster cores, rather than to entire clusters. This will steepen the high-frequency region of the spectrum unless inverse Compton scattering is effective. In many cases accretion flow in the central part of the cluster will be optically thick to electron scattering, resulting in a spectrum featuring optically thick radiative component in addition to power-law regimes. The fitting of these spectra to QSO and AGN observations is discussed, and application to 3C 273 is worked out as an example.

Pacholczyk, A. G.↗
NASA NTRS1989

Adiabatic growth of a black hole in a rotating stellar system

The consequences of slowly adding a massive black hole to the center of a rotating stellar system are considered. Although both the rotation velocity V and the velocity dispersion sigma increase when the black hole is added, the rotation velocity increases faster. The effect goes in the right direction but is too gradual to explain the V/sigma profiles recently observed in several galactic nuclei.

Lee, Man Hoi↗
NASA NTRS1991

Black holes in magnetic monopoles

We study magnetically charged classical solutions of a spontaneously broken gauge theory interacting with gravity. We show that nonsingular monopole solutions exist only if the Higgs field vacuum expectation value v is less than or equal to a critical value v sub cr, which is of the order of the Planck mass. In the limiting case, the monopole becomes a black hole, with the region outside the horizon described by the critical Reissner-Nordstrom solution. For v less than v sub cr, we find additional solutions which are singular at f = 0, but which have this singularity hidden within a horizon. These have nontrivial matter fields outside the horizon, and may be interpreted as small black holes lying within a magnetic monopole. The nature of these solutions as a function of v and of the total mass M and their relation to the Reissner-Nordstrom solutions is discussed.

Lee, Kimyeong↗
NASA NTRS1991

Euclidean black hole vortices

We argue the existence of solutions of the Euclidean Einstein equations that correspond to a vortex sitting at the horizon of a black hole. We find the asymptotic behaviors, at the horizon and at infinity, of vortex solutions for the gauge and scalar fields in an abelian Higgs model on a Euclidean Schwarzschild background and interpolate between them by integrating the equations numerically. Calculating the backreaction shows that the effect of the vortex is to cut a slice out of the Schwarzschild geometry. Consequences of these solutions for black hole thermodynamics are discussed.

Dowker, Fay↗
NASA NTRS1991

Gamma rays and energetic particles from primordial black holes

The standard model of quarks and leptons is used to discuss the signatures of black-hole evaporations. A firm bound on the primordial black hole abundance is obtained from MeV data. It is argued that the MeV bound can be improved by exploiting the new generation of TeV and PeV telescopes.

Halzen, F.↗
NASA NTRS1991

Three-dimensional simulations of black hole tori

The global hydrodynamic nonaxisymmetric instabilities in thick constant angular momentum (l) accretion gas tori in orbit around a Schwarzschild black hole are investigated via 2D and 3D numerical simulations. A radially-wide torus is found to develop and m = 1 nonaxisymmetric density perturbation near the pressure maximum and a trailing spiral wave that extends through the outer part of the torus. This global wave transports angular momentum through the torus, causing the average angular momentum distribution to evolve slowly away from l = constant. The unstable mode drives an accretion flow from the torus into the black hole. The role of accretion is investigated by modeling a wide torus with an inner boundary at the cusp of the Schwarzschild effective potential. In such a torus, accretion is present throughout the evolution; only modest unstable mode growth is observed, and saturation occurs at low amplitude. Comparison simulations performed in the torus equatorial plane show qualitative similarities between the 2D and 3D system, although the 3D modes have a function dependence on height.

Hawley, John F.↗
NASA NTRS1992

The evaluation of GOES black paint materials

The purpose of this paper is to study the contamination effect of black paint materials on the GOES instrument performance. The GOES spacecraft materials were originally selected for their low outgassing properties. Samples of the materials were tested according to the ASTM E-595 test method to fulfill the total mass loss and collected volatile condensable materials criteria for traditional spacecraft material selection. Due to the instrument design, the cavity will experience high temperatures during operation greater than the specified temperature in the ASTM test. As a result of this high cavity temperature, normally stable paint materials on the painted surface may severely outgas even though they have passed the ASTM test. Further enhancement of the contaminant remaining on the mirror by UV irradiation is also a great consideration. This concern prompted an investigation into the outgassing characteristics of the black paints at the predicted operating temperatures.

Chen, Philip T.↗
NASA NTRS1992

Hard X-ray imaging of the Galactic black hole candidate GX 339 - 4

Imaging and spectral observations in the energy range 25-250 keV of the black hole candidate GX 339 - 4 have been obtained with the Energetic X-ray Imaging Telescope Experiment. Observations were made during a balloon flight from Alice Springs, Australia on UT 1989 May 8-10. A single source of nearly 6-sigma significance is detected near the center of the 3.4-deg field of view with a position consistent with GX 339 - 4. This is the first imaging observation of GX 339 - 4 at hard X-ray energies. This result confirms previously reported results from nonimaging experiments showing significant hard X-ray flux up to greater than about 60 keV, with a power-law spectral fit similar to the other black hole candidates such as Cygnus X - 1. The source may have been in an outburst state similar to that recently detected with BATSE on GRO.

Covault, C. E.↗