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1.
The rotational energy of a black hole surrounded by a torus is released through several channels. We have determined that a minor fraction of the energy is released in baryon-poor outflows from a differentially rotating open magnetic flux tube, and a major fraction of about eta/2 is released in gravitational radiation by the torus with angular velocity eta similar 0.2 to 0.5 relative to that of the black hole. We associate the energy emitted in baryon-poor outflows with gamma-ray bursts. The remaining fraction is released in torus winds, thermal emissions, and (conceivably) megaelectron-volt neutrino emissions. The emitted gravitational radiation can be detected by gravitational wave experiments and provides a method for identifying Kerr black holes in the Universe. 相似文献
2.
Black holes are most often detected by the radiation produced when they gravitationally pull in surrounding gas, in a process called accretion. The efficiency with which the hot gas radiates its thermal energy strongly influences the geometry and dynamics of the accretion flow. Both radiatively efficient thin disks and radiatively inefficient thick disks are observed. When the accreting gas gets close to the central black hole, the radiation it produces becomes sensitive to the spin of the hole and the presence of an event horizon. Analysis of the luminosities and spectra of accreting black holes has yielded tantalizing evidence for both rotating holes and event horizons. Numerical simulations imply that the relativistic jets often seen from accreting black holes may be powered in part by the spin of the hole. 相似文献
3.
The physical nature of ultraluminous x-ray sources is uncertain. Stellar-mass black holes with beamed radiation and intermediate black holes with isotropic radiation are two plausible explanations. We discovered radio emission from an ultraluminous x-ray source in the dwarf irregular galaxy NGC 5408. The x-ray, radio, and optical fluxes as well as the x-ray spectral shape are consistent with beamed relativistic jet emission from an accreting stellar black hole. If confirmed, this would suggest that the ultraluminous x-ray sources may be stellar-mass rather than intermediate-mass black holes. However, interpretation of the source as a jet-producing intermediate-mass black hole cannot be ruled out at this time. 相似文献
4.
The presence of young massive stars orbiting on eccentric rings within a few tenths of a parsec of the supermassive black hole in the galactic center is challenging for theories of star formation. The high tidal shear from the black hole should tear apart the molecular clouds that form stars elsewhere in the Galaxy, and transport of stars to the galactic center also appears unlikely during their lifetimes. We conducted numerical simulations of the infall of a giant molecular cloud that interacts with the black hole. The transfer of energy during closest approach allows part of the cloud to become bound to the black hole, forming an eccentric disk that quickly fragments to form stars. Compressional heating due to the black hole raises the temperature of the gas up to several hundred to several thousand kelvin, ensuring that the fragmentation produces relatively high stellar masses. These stars retain the eccentricity of the disk and, for a sufficiently massive initial cloud, produce an extremely top-heavy distribution of stellar masses. This potentially repetitive process may explain the presence of multiple eccentric rings of young stars in the presence of a supermassive black hole. 相似文献
5.
Blandford RD 《Science (New York, N.Y.)》2002,295(5560):1653-1654
Almost 50 years ago, astronomers provided evidence for powerful radio emissions localized in two giant "lobes" on opposite sides of elliptical galaxies. These lobes are now known to be powered by jets emanating from black holes at the centers of the galaxies. In his Perspective, Blandford discusses how the black hole may generate the jets. He highlights the report by Koide et al., who have simulated one mechanism for supplying the jets with energy via a magnetic connection to the gas just outside the black hole's event horizon. 相似文献
6.
N Webb D Cseh E Lenc O Godet D Barret S Corbel S Farrell R Fender N Gehrels I Heywood 《Science (New York, N.Y.)》2012,337(6094):554-556
Relativistic jets are streams of plasma moving at appreciable fractions of the speed of light. They have been observed from stellar-mass black holes (~3 to 20 solar masses, M(⊙)) as well as supermassive black holes (~10(6) to 10(9) M(⊙)) found in the centers of most galaxies. Jets should also be produced by intermediate-mass black holes (~10(2) to 10(5) M(⊙)), although evidence for this third class of black hole has, until recently, been weak. We report the detection of transient radio emission at the location of the intermediate-mass black hole candidate ESO 243-49 HLX-1, which is consistent with a discrete jet ejection event. These observations also allow us to refine the mass estimate of the black hole to be between ~9 × 10(3) M(⊙) and ~9 × 10(4) M(⊙). 相似文献
7.
We report an extremely rapid mechanism for magnetic field amplification during the merger of a binary neutron star system. This has implications for the production of the short class of gamma-ray bursts, which recent observations suggest may originate in such mergers. In detailed magnetohydrodynamic simulations of the merger process, the fields are amplified by Kelvin-Helmholtz instabilities beyond magnetar field strength and may therefore represent the strongest magnetic fields in the universe. The amplification occurs in the shear layer that forms between the neutron stars and on a time scale of only 1 millisecond, that is, long before the remnant can collapse into a black hole. 相似文献
8.
Laurent P Rodriguez J Wilms J Cadolle Bel M Pottschmidt K Grinberg V 《Science (New York, N.Y.)》2011,332(6028):438-439
Because of their inherently high flux allowing the detection of clear signals, black hole x-ray binaries are interesting candidates for polarization studies, even if no polarization signals have been observed from them before. Such measurements would provide further detailed insight into these sources' emission mechanisms. We measured the polarization of the gamma-ray emission from the black hole binary system Cygnus X-1 with the International Gamma-Ray Astrophysics Laboratory Imager on Board the Integral Satellite (INTEGRAL/IBIS) telescope. Spectral modeling of the data reveals two emission mechanisms: The 250- to 400-keV (kilo-electron volt) data are consistent with emission dominated by Compton scattering on thermal electrons and are weakly polarized. The second spectral component seen in the 400-keV to 2-MeV band is by contrast strongly polarized, revealing that the MeV emission is probably related to the jet first detected in the radio band. 相似文献
9.
天然气管道中的黑粉严重影响管输效率与安全,现有的带皮碗、磁铁及钢刷的清管器对黑粉的清除效率较低,且易出现卡球现象。射流作用产生的冲击流场对管内积液、杂质的清除效果较好,基于射流原理提出了利用射流清管器清理天然气管道黑粉的方法。为了达到最佳的射流清除效果,需要优化清管器喷射组件中文氏管喷嘴的关键结构参数。文氏管喷嘴结构包括收缩段、水平段及扩散段,其中扩散段的参数对射流效果起关键作用。基于计算流体力学的原理,以Fluent软件为模拟工具,选定实际气体状态模型定义管道内天然气参数,考虑文氏管喷嘴扩散段中扩散长度与扩散角的影响,对清管器的射流过程进行仿真分析。通过比较不同扩散段参数模型在射流流场中流速和湍流动能的云图以及变化曲线,得到具有最佳射流效果的天然气管道射流清管器喷嘴结构。 相似文献
10.
研究一般球对称带电蒸发黑洞视界附近粒子的能级交错，给出交错能级最大值的表达式，得出一般球对称带电蒸发黑洞非热辐射频率范围是随时间变化的结论． 相似文献
11.
A number of astronomical systems have been discovered that generate collimated flows of plasma with velocities close to the speed of light. In all cases, the central object is probably a neutron star or black hole and is either accreting material from other stars or is in the initial violent stages of formation. Supercomputer simulations of the production of relativistic jets have been based on a magnetohydrodynamic model, in which differential rotation in the system creates a magnetic coil that simultaneously expels and pinches some of the infalling material. The model may explain the basic features of observed jets, including their speed and amount of collimation, and some of the details in the behavior and statistics of different jet-producing sources. 相似文献
12.
Lo KY 《Science (New York, N.Y.)》1986,233(4771):1394-1403
Studies of active galactic nuclei constitute one of the major efforts in astronomy. Massive black holes are the most likely source for the enormous energy radiated from such nuclei. Observations reviewed here suggest unusual activity and the possible existence of a massive black hole in the nucleus of our galaxy. Because of its proximity to Earth, our galactic nucleus can be observed in unsurpassed detail and may serve as the Rosetta stone both for deciphering active galactic nuclei and for confirming the existence of a massive black hole. 相似文献
13.
KS Thorne 《Science (New York, N.Y.)》2012,337(6094):536-538
Numerical simulations have revealed two types of physical structures, made from curved spacetime, that are attached to black holes: tendexes, which stretch or squeeze anything they encounter, and vortexes, which twist adjacent inertial frames relative to each other. When black holes collide, their tendexes and vortexes interact and oscillate (a form of nonlinear dynamics of curved spacetime). These oscillations generate gravitational waves, which can give kicks up to 4000 kilometers per second to the merged black hole. The gravitational waves encode details of the spacetime dynamics and will soon be observed and studied by the Laser Interferometer Gravitational Wave Observatory and its international partners. 相似文献
14.
由黑洞的熵计算其温度 总被引：1，自引：0，他引：1
通过黑洞热力学第一定律,由黑洞的熵来计算黑洞的温度．由此方法算出的史瓦西黑洞和克尔-纽曼黑洞的温度与以前的结果相符,Vaidya黑洞的温度与引入新的乌龟坐标变换后算得的结果一致． 相似文献
15.
Mazzali PA Valenti S Della Valle M Chincarini G Sauer DN Benetti S Pian E Piran T D'Elia V Elias-Rosa N Margutti R Pasotti F Antonelli LA Bufano F Campana S Cappellaro E Covino S D'Avanzo P Fiore F Fugazza D Gilmozzi R Hunter D Maguire K Maiorano E Marziani P Masetti N Mirabel F Navasardyan H Nomoto K Palazzi E Pastorello A Panagia N Pellizza LJ Sari R Smartt S Tagliaferri G Tanaka M Taubenberger S Tominaga N Trundle C Turatto M 《Science (New York, N.Y.)》2008,321(5893):1185-1188
The only supernovae (SNe) to show gamma-ray bursts (GRBs) or early x-ray emission thus far are overenergetic, broad-lined type Ic SNe (hypernovae, HNe). Recently, SN 2008D has shown several unusual features: (i) weak x-ray flash (XRF), (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SN Ic HNe, and (iv) development of helium lines as in SNe Ib. Detailed analysis shows that SN 2008D was not a normal supernova: Its explosion energy (E approximately 6x10(51) erg) and ejected mass [ approximately 7 times the mass of the Sun (M(middle dot in circle))] are intermediate between normal SNe Ibc and HNe. We conclude that SN 2008D was originally a approximately 30 M(middle dot in circle) star. When it collapsed, a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes. 相似文献
16.
Corbel S Fender RP Tzioumis AK Tomsick JA Orosz JA Miller JM Wijnands R Kaaret P 《Science (New York, N.Y.)》2002,298(5591):196-199
We have detected, at x-ray and radio wavelengths, large-scale moving jets from the microquasar XTE J1550-564. Plasma ejected from near the black hole traveled at relativistic velocities for at least 4 years. We present direct evidence for gradual deceleration in a relativistic jet. The broadband spectrum of the jets is consistent with synchrotron emission from high-energy (up to 10 tera-electron volts) particles that were accelerated in the shock waves formed within the relativistic ejecta or by the interaction of the jets with the interstellar medium. XTE J1550-564 offers a rare opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of relativistic jets from Galactic x-ray binaries and active galactic nuclei. 相似文献
17.
In the quarter century since the first optical identification of a "radio star" (3C 48), astronomers have come to general agreement that the underlying quasar energy source is accretion onto a massive black hole. There is much less agreement on the detailed physics of the processes by which this energy is converted to the forms observed, but this has not prevented the objects from serving as valuable probes of the universe at distant times and places. 相似文献
18.
Schilling G 《Science (New York, N.Y.)》2000,290(5493):926-927
Most astrophysicists puzzling over what causes gamma ray bursts--short, intense explosions of high-energy photons that occur deep in space--now agree that the answer is a hypernova, the blast of energy released when a supermassive star collapses into a black hole. Two papers in this issue of Science (pp. 953 and 955), reporting on new x-ray observations of two gamma ray bursts, argue that the hypernova model tells only half of the story. On its way to becoming a black hole, the authors propose, the supermassive star actually collapses twice. 相似文献
19.
DE Young DS 《Science (New York, N.Y.)》1991,252(5004):389-396
Astrophysical jets are linear structures associated with stars and galaxies which span about seven orders of magnitude in size; the largest jets emanating from galaxies are about 100 times the size of our galaxy and are the largest single objects in the universe. Jets associated with stars are composed of ionized gas moving away from the star with velocities of a few hundred kilometers per second. Extragalactic jets are composed of relativistic particles, magnetic field, and probably additional amounts of cooler ionized plasma either originally ejected in the jet or entired by it out of the surrounding gaseous medium. The initial outflow velocity for extragalactic jets may be relativistic, and average outflow speeds of several thousand kilometers per second are likely. The energy flux carried by extragalactic jets may be in excess of 10(46) ergs per second, depending upon the nature of the jet. A definition of jet properties, deduced from their interaction with the ambient medium, can place essential constraints on models for the central power source in the parent galaxy or quasi-stellar object where they originate. 相似文献
20.
van Putten MH 《Science (New York, N.Y.)》1999,284(5411):115-118
The coalescence of a neutron star and a black hole in a binary system is believed to form a torus around a Kerr black hole. A similarly shaped magnetosphere then results from the remnant magnetic field of the neutron star. In the strong-field case, it contains a cavity for plasma waves located between the barrier of the gravitational potential and the surrounding torus. This cavity may be unstable to superradiance of electromagnetic waves. Superradiant amplification of such waves, initially excited by turbulence in the torus, should inflate into a bubble in a time as short as approximately 0.75 (1 percent/&cjs3539;epsilon&cjs3539;2)(M/7M middle dot in circle) seconds approximately 0.15 to 1.5 seconds, assuming an efficiency &cjs3539;epsilon&cjs3539;2 = 0.5 to 5 percent and a mass M = 7M middle dot in circle. These bubbles may burst and repeat, of possible relevance to intermittency in cosmological gamma-ray bursts. The model predicts gamma-ray bursts to be anticorrelated with their gravitational wave emissions. 相似文献