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ORIGINS OF BLACK HOLES IN UNIVERSE.
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Contends that existence is still theoretical because there are no measurable or observable phenomena.... More...
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Paper Abstract:
Contends that existence is still theoretical because there are no measurable or observable phenomena.
Paper Introduction:
Black holes, sometimes called "collapsars," are a class of astronomical object which has attracted great attention both from astrophysicists and the general public in the past two decades. According to theory, if an astronomical body is large or dense enough, its gravitational escape velocity will exceed the velocity of light: thus no radiation from it can escape to the outside Universe. It disappears within an "event horizon." Such an object, from which not even light can escape, would seem to be undetectable, yet black holes are of great interest to astronomers and physicists. A number of indirect methods of detecting black holes have been proposed, and indeed a number of black hole "candidates" have been identified. However, black holes remain a theoretical construct, since no persuasive indirect observational evidence has been found that would rule
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L. Someof this will escape, and some will fall through the event horizon andvanish. If a black hole were one member of a "close" binary system, anaccretion disk might also form, detectable in the same way as for that of agalactic-core black hole. By the early twentieth century, the scope of both physics andastronomy had vastly expanded. Above thatmass, the crushing effect of the core's gravity would be so great that evenneutrons could not hold their form. It seemed to have no practical applicationto astronomical research. Unfortunately, the optical defectsof the Hubble Telescope, discovered shortly after its launch in 199 , nowpreclude its settling the matter. It has also been suggested that black holes could form underconditions other than those of supernovae or galactic cores. In 1974, moreover, physicist Stephen Hawking made a startlingtheoretical discovery: under the laws of quantum mechanics, given certainconditions, particles can "tunnel" out through the event horizon of a blackhole (1: 264-65). New York: Scientific American Library, 1989.3. The general concept behind black holes is a surprisingly old one. Robert Oppenheimer (the "father of the atomic bomb")and his student Hartland Snyder developed a new theory which outlinedconditions under which a black hole might actually be formed (4: 65).Under certain circumstances a massive star can suffer a catastrophicexplosion, called a supernova, which blows the outer layers of the star offinto space, while the core of the star collapses to a mass of tightlypackedneutrons--so dense that a star the mass of the Sun would be only a fewmiles in diameter. This may seem paradoxical. For a generationafter they were theorized, neutron stars remained a purely theoreticalconstruct, but neutron stars have now been positively identified insupernova remnants, including the Crab Nebula. A number of indirect methods of detectingblack holes have been proposed, and indeed a number of black hole"candidates" have been identified. Black Holes, Quasars, and the Universe. M.; Schramm, D. Within the black hole's event horizon--undetectable from the outside--the core would continue its collapse,reaching states of matter which are still at the edge of our understandingof physics. An alternative explanation, now the most popular one, is that quasarsare produced by immense black holes, with a mass millions or billions oftimes greater than that of the sun. As it approaches,"tidal" forces will distort it and finally rip it apart into plasma. From individual galaxies to theUniverse as a whole, there is evidence that the luminous matter we observeis vastly outweighed by "missing"--actually simply nonluminous or"underluminous"--matter, detected only by its gravitational influence (4:15 -51). It disappears withinan "event horizon." Such an object, from which not even light can escape,would seem to be undetectable, yet black holes are of great interest toastronomers and physicists. Accordingto theory, if an astronomical body is large or dense enough, itsgravitational escape velocity will exceed the velocity of light: thus noradiation from it can escape to the outside Universe. In some binary systems, as one star expands intoits red-giant phase, matter from its outer layers falls across onto theother member of the binary, forming an accretion disk around it beforefinally falling in. W.; Israel, W., eds. Astrophysicists tend tobe confident that black holes exist. Black holes, sometimes called "collapsars," are a class ofastronomical object which has attracted great attention both fromastrophysicists and the general public in the past two decades. Then,in 1939, physicist J. This is the mechanism behind ordinary novae (not to beconfused with supernovae), Beta Lyrae stars, and some other well-knownclasses of object. Thus the current state of observational research on black holesremains tantalizing, fascinating, and frustrating. However, thiswould be ambiguous, since it is also possible that some supernovae blowthemselves entirely apart, leaving nothing--not even a black hole--at thecenter. Astronomers need wait trillion-trillions of years for such explosions to prove the existence of blackholes, since the previous "leakage" is, at least in theory, detectable. Quarks, the most fundamental of all particles, have in theoryno size at all: they are pure points. It still remained, however, a conceptwith no particular connection to specific problems in astrophysics. Literature Cited1 Hawking, S. Blackholes remain the "prime candidates" for quasars and for the relatedphenomena of intense radio, light and X-radiation from the cores ofgalaxies. The radius of a black hole's event horizon is still called theSchwartzschild radius in his honor. Theoretical means also exist for detecting black holes formed bysupernova explosions as well. Many possible explanations have been put forward, from "browndwarfs" (stars too small to shine from nuclear reactions) to black holes.None of these, however, has yet gained general acceptance. Some, however, will be trapped in orbit around the black hole,orbiting at nearly the speed of light, just outside the event horizon. Sky and Telescope, 77:48 ; 1989, May.4. From Quarks to the Cosmos. Another strand of astronomical study also led to interest in blackholes. Because they appeared like stars, they werecalled quasi-stellar radio sources, a name contracted to quasars (1: 297-99). At present, however,, black holes remaintheoretical constructs, for which conclusive observational proof islacking. This radiation, coming not "from" the black hole, but from itsimmediate vicinity, can be detected from a distance (2: 145). This process could, indeed, liberate enough radiationin the immediate neighborhood of the black hole to power a quasar. Anytime two particles of matter in different orbits collide -at near-lightvelocities--enormous kinetic energy will be released and turned partly intoradiation. Boston: Houghton Mifflin, 1976.----------------------- 9 SN 1987A and Its Ultrafast Pulsar. Cambridge: Cambridge Univ. A number of candidate X-ray objects have beenidentified as possible stellar-mass black holes formed by supernovae; amongthese are Cygnus X-1 and SS433 in our galaxy, and LMC X-1 and LMC X-3 inthe Large Magellanic Cloud (1: 31 ff). One in theyear 1 54, recorded by Chinese astronomers, is believed to have producedthe dramatic Crab Nebula in Taurus. A massive core would thus continue itscollapse. As with the Roach Motel, nothing cancheck out of a black hole -but any matter caught in its gravitational fieldcan check in, falling onto and through the event horizon. Laplace argued that ifa star were large enough, or dense enough, to have a surface escapevelocity greater than the velocity of light, its light would be trapped,and it would be undetectable by any telescope (4: 65). A. A neutron star could only form if the remaining core of a supernovawas below a certain mass, equivalent to about two solar masses. 3 Years of Gravitation. Perhaps, then, the final state of acollapsed supernova core would be a dimensionless mass of quarks (2: 1 4). The answer is that when a black hole is that the eventhorizon works only in one direction. In the 196 s, astronomers detected very distant, very powerful, andvery compact radio sources. Once through theevent horizon it is lost to view. Shortly before his death during World WarI, the German physicist Karl Schwartzschild carried out the firstscientific analysis of the properties of what we now call black holes (2:45). In the body of this study, the conditionsunder which black holes could form will be outlined, possible classes ofblack holes surveyed, and the current state of observation reviewed. Moreover, extremely massive and compact objects,perhaps "burnedout" quasars, are known to exist in many galaxies, perhapsincluding our own. Press, 1987.2. Neutron stars, it is worth noting, were once in the sameobservational limbo as black holes are today. Soon its escape velocity would exceed the velocity of light, andit would become a black hole. In the veryearly Universe, less than 1 -43 seconds after the Big Bang, the Universewas so dense that large numbers of black holes could spontaneously form.It is worth noting in this connection that "missing mass" has in recentyears become a major problem in astronomy. However, Laplace'sidea was ignored and forgotten. Some of this would form an "accretion disk" around the black hole'sevent horizon, and anything falling into the black hole would inevitablycrash into the accretion disk first, shedding most of its kinetic energy asradiation as it did. If a lone star blew up, leaving behind ablack hole, all that could be detected from a distance would be a negative:a supernova remnant with no neutron star at its center. Schorn, R. Likewise, if we found a starcluster in which the velocities of the stars were too great to hold thecluster together unless a great invisible mass were present in the centerof the cluster. Such a collapsed star was called a neutron star, andits surface escape velocity would be a large fraction of the velocity oflight. The possibility thus remains that future observations willdemonstrate that some object is indeed a black hole, even if we cannot seethrough its event horizon. Observational astronomers are moreskeptical, not because they disbelieve the astrophysicists, but because nounambiguous observational evidence for black holes has yet been detected.It was widely hoped that the Hubble Space Telescope would provide sharpenough images of galactic nuclei to allow alternative theories for massivegalactic core objects to be tested, allowing the supermassive black holemodel to be either proved or disproved. Dense star-clusters, wracked by near-continuous stellar collisions or "chain-reaction" supernovae were alsoconsidered, but they also pose severe theoretical difficulties (1: 3 2-3 4). Quasars are both the most luminous and the most distant objectsdetected in the Universe. How could black holes, from which nolight whatsoever can escape, be the power source for the brightest objectsin the Universe? What, asked the astrophysicists, could be sosmall and yet so bright? N. Supernovae are rare but well-known astronomical events. Lederman, L. Yet they are very small--not much larger thanthe size of the Solar System. Shipman, H. Recently, astronomers foundevidence of a new-born neutron star (or "pulsar") within the debris of the1987 Magellanic Cloud supernova (3: 48 ). Detection prospects are better for supernova-formed black holes inbinary-star systems or star clusters (1:3 6-3 7). In1796, the French mathematician Pierre Simon, better known as the Marquis deLaplace, applied Newton's theory of gravitation to the problem of light,which was already known to have a finite velocity. Indeed -over a time period very much longer than thecurrent age of the Universe--any black hole must eventually leak so much ofits mass that it will finally cease to be a black hole and will "explode"back out into the visible universe. But until it passes through the eventhorizon, it remains detectable. The event horizon of such a massiveblack hole would, indeed, be about the right size to "fit" the observedbehavior of quasars. The nature and composition of stars were stillunknown, and no stellar distance had yet been measured. They were proposed andanalyzed theoretically a generation before they were observationallydetected. Now, if a supermassive black hole were to form at the turbulent coreof a young galaxy, huge masses of matter would constantly be falling intoit. In 1987, a supernova in the MilkyWay's satellite galaxy, the Large Magellanic Cloud, attained naked-eyevisibility at a distance of about 15 , light years. Now, imagine an object, say a star or aspaceship, which passes dangerously near a black hole. One possibility was "superstars"--starlikeobjects thousands of times more massive than the largest ordinary stars.Closer theoretical examination, however, ruled out such superstars as thesources of quasars (1: 299-3 ). If we found a star thatappeared to be in orbit around "nothing," this would be strong evidencethat it was in fact orbiting a black hole. However, black holes remain atheoretical construct, since no persuasive indirect observational evidencehas been found that would rule out alternative explanations for these"candidate" objects (1: 321-23).
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