Combat Arms
\n 2869 Grove Way
\n Castro Valley, California 94546-6709
\n Telephone (415) 538-6544<\/p>\n
The following material was downloaded from the NASA SpaceLink
\nBBS at the National Aeronautics and Space Administration, George C.
\nMarshall Space Flight Center, Marshall Space Flight Center, Alabama
\n35812 on 11\/16\/88.<\/p>\n
B L A C K H O L E S I N S P A C E
\n————————————————————-<\/p>\n
There is much more to black holes than meets the eye. In fact,
\nyour eyes, even with the aid of the most advanced telescope, will
\nnever see a black hole in space. The reason is that the matter
\nwithin a black hole is so dense and has so great a gravitational pull
\nthat it prevents even light from escaping.<\/p>\n
Like other electromagnetic radiation (radio waves, infrared
\nrays, ultraviolet radiation, X-rays, and gamma radiation), light is
\nthe fastest traveler in the Universe. It moves at nearly 300,000
\nkilometers (about 186,000 miles) per second. At such a speed, you
\ncould circle the Earth seven times between heartbeats.<\/p>\n
If light can’t escape a black hole, it follows that nothing else
\ncan. Consequently, there is no direct way to detect a black hole.<\/p>\n
In fact, the principal evidence of the existence of black holes
\ncomes not from observation but from solutions to complex equations
\nbased on Einstein’s Theory of General Relativity. Among other
\nthings, the calculations indicate that black holes may occur in a
\nvariety of sizes and be more abundant than most of us realize.<\/p>\n
MINI BLACK HOLES<\/p>\n
Some black holes are theorized to be nearly as old as the Big
\nBang, which is hypothesized to have started our Universe 10 to 20
\nbillion years ago. The rapid early expansion of some parts of the
\ndense hot matter in this nascent Universe is said to have so
\ncompressed less rapidly moving parts that the latter became
\nsuperdense and collapsed further, forming black holes. Among the
\nholes so created may be the submicroscopic mini-black holes.<\/p>\n
A mini-black hole may be as small as an atomic particle but
\ncontain as much mass (material) as Mount Everest. Never
\nunderestimate the power of a mini-black hole. If some event caused
\nit to decompress, it would be as if millions of hydrogen bombs were
\nsimultaneously detonated.<\/p>\n
HOW STARS DIE<\/p>\n
The most widespread support is given to the theory that a black
\nhole is the natural end product of a giant star’s death. According
\nto this theory, a star like our Sun and others we see in the sky
\nlives as long as thermal energy and radiation from nuclear reactions
\nin its core provide sufficient outward pressure to counteract the
\ninward pressure of gravity caused by the star’s own great mass.<\/p>\n
When the star exhausts its nuclear fuels, it succumbs to the
\nforces of its own gravity and literally collapses inward. According
\nto equations derived from quantum mechanics and Einstein’s Theory of
\nGeneral Relativity, the star’s remaining mass determines whether it
\nbecomes a white dwarf, a neutron star, or black hole.<\/p>\n
WHITE DWARFS<\/p>\n
Stars are usually measured in comparison with our Sun’s mass. A
\nstar whose remaining mass is about that of our Sun condenses to
\napproximately the size of Earth. The star’s contraction is halted by
\nthe collective resistance of electrons pressed against each other and
\ntheir atomic nuclei. Matter in this collapsed star is so tightly
\npacked that a piece the size of a sugar cube would weigh thousands of
\nkilograms. Gravitational contraction would also have made the star
\nwhite hot. It is appropriately called a white dwarf.<\/p>\n
Astronomers have detected white dwarfs in space. The first
\ndiscovery was a planet-sized object that seemed to exert a
\ndisproportionately high gravitational effect upon a celestial
\ncompanion, the so call dog star Sirius, which is about 2.28 times our
\nSun’s mass. It appeared that this planet-sized object would have to
\nbe about as massive as our Sun to affect Sirius as it did. Moreover,
\nspectral analysis indicated the star’s color was white.<\/p>\n
Based upon these and other studies, astronomers concluded that
\nthey had found a white dwarf. However, it took many years after the
\ndiscovery in 1914 before most scientists accepted the fact that an
\nobject thousands of times denser than anything possible on Earth
\ncould exist.<\/p>\n
NEUTRON STARS AND SUPERNOVAS<\/p>\n
Giant stars usually lose most of their mass during their normal
\nlifetimes. If such a star still retains 1 1\/2 to 3 solar masses
\nafter exhaustion of its nuclear fuels, it would collapse to even
\ngreater density and smaller size than the white dwarf. The reason is
\nthat there is a limit on the amount of compression electrons can
\nresist in the presence of atomic nuclei.<\/p>\n
In this instance, the limit is breached. Electrons are
\nliterally driven into atomic nuclei, mating with protons to form
\nneutrons and thus transmuting nuclei into neutrons. The resulting
\nobject is aptly called a neutron star. It may be only a few
\nkilometers in diameter. A sugar-cube size piece of this star would
\nweigh about one-half a trillion kilograms.<\/p>\n
Sometimes, as electrons are driven into protons in atomic
\nnuclei, neutrinos are blown outward so forcefully that they blast off
\nthe star’s outer layer. This creates a supernova that may
\ntemporarily outshine all of the other stars in a galaxy.<\/p>\n
The most prominent object believed to be a neutron star is the
\nCrab Nebula, the remnant of a supernova observed and reported by
\nChinese astronomers in 1504. A star-like object in the nebula
\nblinks, or pulses, about 30 times per second in visible light, radio
\nwaves, and X and gamma rays. The radio pulses are believed to result
\nfrom interaction between a point on the spinning star and the star’s
\nmagnetic field. As the star rotates, this point is theorized
\nalternately to face and be turned away from Earth. The fast rotation
\nrate implied by the interval between pulses indicates the star is no
\nmore than a few kilometers in diameter because if it were larger, it
\nwould be torn apart by centrifugal force.<\/p>\n
PULSARS<\/p>\n
Radio telescopes have detected a large number of other objects
\nwhich send out naturally pulsed radio signals. They were named
\npulsars. Like the object in the Crab Nebula, they are presumed to be
\nrotating neutron stars.<\/p>\n
Of these pulsars, only the Vela pulsar–which gets its name
\nbecause of its location in the Vela (Sails) constellation–pulses at
\nwavelengths shorter than radio. Like the Crab pulsar, the Vela
\npulsar also pulses at optical and gamma ray wavelengths. However,
\nunlike the Crab pulsar, it is not an X-ray pulsar. Aside from the
\nmystery generated by these differences, scientists also debate the
\nreasons for the pulses at gamma, X-ray and optical frequencies. As
\nnoted earlier, they agree on the origin of the radio pulses.<\/p>\n
BLACK HOLES<\/p>\n
When a star has three or more solar masses left after it
\nexhausts its nuclear fuels, it can become a black hole.<\/p>\n
Like the white dwarf and neutron star, this star’s density and
\ngravity increase with contraction. Consequently, the star’s
\ngravitational escape velocity (speed needed to escape from the star)
\nincreases. When the star has shrunk to the Schwarzschild radius,
\nnamed for the man who first calculated it, its gravitational escape
\nvelocity would be nearly 300,000 kilometers per second, which is
\nequal to the speed of light. Consequently, light could never leave
\nthe star.<\/p>\n
Reduction of a giant star to the Schwarzschild radius represents
\nan incredible compression of mass and decrease in size. As an
\nexample, mathematicians calculate that for a star of 10 solar masses
\n(ten times the mass of our Sun) after exhaustion of its nuclear
\nfuels, the Schwarzschild radius is about 30 kilometers.<\/p>\n
———————————————————————
\n According to the Law of General Relativity, space and time are
\nwarped, or curved, by gravity. Time is theorized TO POINT INTO THE
\nBLACK HOLE FROM ALL DIRECTIONS. To leave a black hole, an object,
\neven light would have to go backward in time. Thus, anything falling
\ninto a black hole would disappear from our Universe.
\n———————————————————————<\/p>\n
The Schwarzschild radius becomes the black hole’s “event
\nhorizon”, the hole’s boundary of no return. Anything crossing the
\nevent horizon can never leave the black hole. Within the event
\nhorizon, the star continues to contract until it reaches a space-time
\nsingularity, which modern science cannot easily define. It may be
\nconsidered a state of infinite density in which matter loses all of
\nits familiar properties.<\/p>\n
Theoretically, it may take less than a second for a star to
\ncollapse into black hole. However, because of relativistic effects,
\nwe could never see such an event. This is because, as demonstrated
\nby comparison of clocks on spacecraft with clocks on Earth, gravity
\ncan slow, perhaps even stop, time. The gravity of the collapsing
\nstar would slow time so much that we would see the star collapsing
\nfor as long as we watched.<\/p>\n
Once a black hole has been formed, it crushes into a singularity
\nanything crossing its event horizon. As the black hole devours
\nmatter, its event horizon expands. This expansion is limited only by
\nthe availability of matter. Incredibly vast black holes that harbor
\nthe crushed remains of billions of solar masses are theoretically
\npossible.<\/p>\n
Evidence that such superdense stars as white dwarfs and neutron
\nstars do exist has supported the idea that black holes, representing
\nwhat may be the ultimate in density, must also exist. Potential
\nblack holes, stars with three or more times the mass of our Sun,
\npepper the sky. But how can astronomers detect a black hole?<\/p>\n
HOW BLACK HOLES MAY BE INDIRECTLY DETECTED<\/p>\n
Scientists found indirect ways of doing so. The methods depends
\nupon black holes being members of binary star systems. A binary star
\nsystem consists of two stars comparatively near to and revolving
\nabout each other. Unlike our Sun, most stars exist in pairs.<\/p>\n
If one of the stars in a binary system had become a black hole,
\nthe hole would betray its existence, although invisible, by its
\ngravitational effects upon the other star. These effects would be in
\naccordance with Newton’s Law: attractions of two bodies to each other
\nare directly proportional to the square of the distance between them.
\nThe reason is that outside of its event horizon, a black hole’s
\ngravity is the same as other objects’.<\/p>\n
Scientists also have determined that a substantial part of the
\nenergy of matter spiraling into a black hole is converted by
\ncollision, compression, and heating into X- and gamma rays displaying
\ncertain spectral characteristics. The radiation is from the material
\nas it is pulled across the hole’s event horizon, its radiation cannot
\nescape.<\/p>\n
WORMHOLES<\/p>\n
Some scientists speculate that matter going into a black hole
\nmay survive. Under special circumstances, it might be conducted via
\npassages called “wormholes” to emerge in another time or another
\nuniverse. Black holes are theorized to play relativistic tricks with
\nspace and time.<\/p>\n
NASA ORBITING OBSERVATORY OBSERVATIONS<\/p>\n
Black hole candidates–phenomena exhibiting black hole
\neffects–have been discovered and studied through such NASA
\nsatellites as the Small Astronomy Satellites (SAS) and the much
\nlarger Orbiting Astronomical Observatories (OAO) and High Energy
\nAstronomical Observatories (HEAO). The most likely candidate is
\nCygnus X-1, an invisible object in the constellation Cygnus, the
\nswan. Cygnus X-1 means that it is the first X-ray source discovered
\nin Cygnus. X-rays from the invisible object have characteristics
\nlike those predicted from material as it falls toward a black hole.
\nThe material is apparently being pulled from the hole’s binary
\ncompanion, a large star of about 30 solar masses. Based upon the
\nblack hole’s gravitational effects on the visible star, the hole’s
\nmass is estimated to be about six times of our Sun. In time the
\ngargantuan visible star could also collapse into a neutron star or
\nblack hole or be pulled piece by piece into the existing black hole,
\nsignificantly enlarging the hole’s event horizon.<\/p>\n
BLACK HOLES AND GALAXIES<\/p>\n
It is theorized that rotating black holes, containing the
\nremains of millions or billions of dead stars, may lie at the centers
\nof galaxies such as our Milky Way and that vast rotating black holes
\nmay be the powerhouses of quasars and active galaxies. Quasars are
\nbelieved to be galaxies in an early violent evolutionary stage while
\nactive galaxies are marked by their extraordinary outputs of energy,
\nmostly from their cores.<\/p>\n
According to one part of the General Theory of Relativity called
\nthe Penrose Process, most of the matter falling toward black holes is
\nconsumed while the remainder is flung outward with more energy than
\nthe original total falling in. The energy is imparted by the hole’s
\nincredibly fast spin. Quiet normal galaxies like our Milky Way are
\nsaid to be that way only because the black holes at their centers
\nhave no material upon which to feed.<\/p>\n
This situation could be changed by a chance break-up of a star
\ncluster near the hole, sending stars careening into the hole. Such
\nan event could cause the nucleus of our galaxy to explode with
\nactivity, generating large volumes of lethal gamma radiation that
\nwould fan out across our galaxy like a death ray, destroying life on
\nEarth and wherever else it may have occurred.<\/p>\n
BLACK HOLES AND GALACTIC CLUSTERS<\/p>\n
Some astronomers believe that the gravity pulls of gigantic
\nblack holes may hold together vast galactic clusters such as the
\nVirgo cluster consisting of about 2500 galaxies. Such clusters were
\nformed after the Big Bang some 10 to 20 billion years ago. Why they
\ndid not spread randomly as the Universe expanded is not understood,
\nas only a fraction of the mass needed to keep them together is
\nobservable. NASA’s Hubble Space Telescope and AXAF Telescope,
\nscheduled for a future Shuttle launch, will provide many more times
\nthe data than present ground and space observatories furnish and
\nshould contribute to resolving this and other mysteries of our
\nUniverse.<\/p>\n
BLACK HOLES AND OUR UNIVERSE<\/p>\n
Our universe is theorized to have begun with a bang that sent
\npieces of it outward in all directions. As yet, astronomers have not
\ndetected enough mass to reverse this expansion. The possibility
\nremains, however, that the missing mass may be locked up in
\nundetectable black holes that are more prevalent than anyone
\nrealizes.<\/p>\n
If enough black holes exist to reverse the universe’s expansion,
\nwhat then? Will all of the stars, and galaxies, and other matter in
\nthe universe collapse inward like a star that has exhausted its
\nnuclear fuels? Will one large black hole be created, within which
\nthe universe will shrink to the ultimate singularity?<\/p>\n
Extrapolating backward more than 10 billion years, some
\ncosmologists trace our present universe to a singularity. Is a
\nsingularity both the beginning and end of our universe? Is our
\nuniverse but a phase between singularities?<\/p>\n
These questions may be more academic than we realize.
\nScientists say that, if the universe itself is closed and nothing can
\nescape from it, we may already be in a black hole.
\ne.
\nScientists say that, if the universe itself is closed and nothing can
\nesc<\/p>\n
