Given that the gravitational force is allegedly mediated by the graviton and nothing can escape the gravitational potential energy well that is a black hole (presumably not even the graviton) how can a black hole 'alert' the rest of the universe to it's prescence?
212373
A black hole, by definition, doesn't emit light; photons can enter the event horizon of a black hole, but cannot emerge from it. If you can't see a black hole, then how do you know it's there?? In order to detect a black hole, you have to be devious and use indirect methods. \nThe method of detecting dark objects by noting their gravitational effect on luminous objects is a very old one. \n\nThe planet Neptune was first discovered from its gravitational effect on the planet Uranus. \nThe white dwarf Sirius B was first discovered from its gravitational effect on the star Sirius A. \nA black hole can be discovered from its gravitational effect on luminous matter (stars and/or hot gas).\n\nIf a black hole exists in a close binary system, it can be detected indirectly. Gas ripped from the companion star will spiral in toward the black hole. As it does so, it is heated up (by tidal heating, and by friction as it rubs against neighboring gas). The hot gas emits X-rays as it undergoes its death spiral to the event horizon. (Once it's inside the event horizon, we don't see the gas any more, but it's highly visible as long as it's outside.) If you are hunting for black holes, it's good to start by looking for binary star systems which are also strong X-ray sources. \n\nAbout a dozen other black hole candidates, with masses up to 10 solar masses or so, have been found in binary star systems within our galaxy. (We don't expect too many black hole stellar remnants, given the scarcity of the extremely massive stars which are their precursors.) \nAn interesting recent development in astronomy is that supermassive black holes (that is, black holes more than a million times the mass of the Sun) are found at the centers of many galaxies. Our own galaxy, for instance, has a black hole with mass 2.6 million Msun at its center, 8000 parsecs away from us. Our own galactic black hole is actually fairly wimpy. The Andromeda Galaxy, 700,000 parsecs away, has a black hole with a mass of 30 million Msun. \n\nHow do you go about hunting such supermassive black holes? As usual, you go about it indirectly, by looking at the orbital motion of gas and stars near the centers of galaxies. For instance, the observation of stars near the center of our own galaxy has revealed that they are orbiting a massive object with M = 2.6 million Msun. The closest star to this massive object comes within 17 light-hours (120 A.U.) of its center. The only plausible way to cram 2.6 million solar masses of stuff into a sphere 120 A.U. in radius is to make it all into a single big black hole. (For instance, if you tried to make a cluster of a million neutron stars 120 A.U. in radius, the collisions between neutron stars would make them all merge into a single big black hole within a few hundred thousand years.)
14789
a black hole is a point of infinite density and gravitational pull. First of all you would be dead from different gravitational pulls from the black hole. Second of all, time from your perspective would stop, assuming that einstein is correct and your image would be spread out over an infinite period of time so your friend would see nothing.
404718
"...Does the black hole continue to increase in mass and increase the gravitational affect?..."\nWe haven't been studying black holes long enough yet to determine if their mass does increase from all the material being drawn in. Theoretically it would.\n\n"...does all that stuff get shot out in another direction?..."\nExactly what happens to material that disappears beyond the event horizon of black holes isn't known for sure because there's no way science can observe what goes on there. A few speculations persist about so-called  'white holes,' the drain of black holes where everything re-appears in another universe or dimension.\n\n"...Do black holes ever die? And if so, what happens to them?..."\nAgain, science doesn't know because the observational evidence just isn't there. However, Stephen Hawking has developed a workable theory showing that over great lengths of time black holes can actually radiate some of their energy and in time would evaporate.
466431
When a star gets big enough, and it finally dies by exploding, some of the central core of the star gets compressed from the explosion.  If there is enough left (about 4 times the mass of our sun), then it collapses into itself and gets so dense and so compressed that the gravity it creates is so great that nothing can escape.\nGravity is the force that any object with mass creates, the more mass the more gravity (the heavier you are if you are on the surface).  Black holes are so massive that the gravity they create is so powerful that not even light can escape and it looks black.  Since nothing can escape its gravity, its like a hole that things only fall into.\nThat's where the name came from.\n\nThere is a lot more physics involved, but that's the basic concept.
21627
By definition, something which cannot be detected does not exist (note: something that potentially COULD be detected, but hasn't been DOES exist; it just hasn't been detected).  For example, there can be large technological metropolis filled with aliens on a planet just inside of a black hole, but because we can never observe information from the hole, we say the city doesn't exist.  Same with the 'outside' of the universe.  If information can never enter the universe, than anything outside of the universe doesn't exist.  Such objects, the black hole city and the 'outside' of the universe, fall within the realm of metascience or philosophy.  However, just as we cannot prove they exist, we likewise cannot collect sufficient information to say that they don't, and it is this inability to test that makes it philosophy, not science.  PS: The black hole 'city' example was ridiculous, but it was more poetic than saying 'quantum particle' ;)
339644
Excellent question! It's got many of us thinking.\n\nThe nature of black holes is such that not everything cannot escape from it, contrary to popular belief.\n\nBlack holes will emit high energy photons in a gamma ray burst.\n\nDavid Cline at UCLA suggests they are the detonation of microscopic black holes formed in the Big Bang, which most astronomers believe was the beginning of the universe. If the idea is right, billions and billions of relatively nearby, primordial black holes are just waiting to explode. \n\nSome may exist just beyond the orbit of Pluto, based on the math.\n\nThere was a recent article in New Scientist regarding a similar topic to this. Another good point for research would be NASA's Chandra telescope pages.\n\nI'll certainly be discussing this one with my team!
358611
It is possible that black holes are the catalyst behind the big crunch, which is the end version of the big bang. Once all of the black holes in existence collect enough matter and energy, they could combine gravitationaly to create one massive black hole that simply repeats the big bang over and over.\n\nBlack holes do not reflect anything, so I don't believe the ignition of the sun was caused by a black hole. \nBlack Hole Info:\n1.They represent matter/energy in its purest form. (All matter and energy is coalesced into one single state of energy)\n\n2.They represent the possible end of our universe.(big crunch)\n\n3.They are the single largest gravitational entity theorized to exist.\n\n4.They are one of the few places that prohibit the propagation of light, so no reflection.\n\n5.The laws of nature at a black hole are completely different from anywhere else in the universe.
271671
Nope.  Whoever told you this has been watching too much science fiction.\n\nBlack holes are just collapsed stars, and their gravity is no bigger than any other star (except to things that are very close to it).  There are enormous black holes at the center of galaxies, but these don't pose a threat to the majority of the galaxy ... and the earth is way out near the edge of our galaxy.  And there is no black hole even theorized that is big enough to swallow entire galaxies.
551146
Because it is only theoretical . And also, if one was ever discovered, the satellite would be sucked in and all the data would be lost. If scientists ever find a safe way to observe black holes, we will know much more.
427458
no. \nthe stress-energy tensor tells us how the energy is spread, and moves, across spacetime.\nthe gravitational constant is a parameter that determines to what degree 1 kg of mass (for instance) will "warp" the spacetime. \n\nso, you can't derive it from the einstein equation.\n\nin fact, relativists usually set the gravitational constant to = 1, so that they don't have to deal with it. although it's essential when you're trying to determine exactly what your physical predictions will be, it's not really an active element of einstein's theory. it just kind of sits there.
78871
Like all gravitationally-formed objects, a black hole is roughly spherical in shape (like planets and stars, a rotating black hole will be slightly flattened at the poles.)  According to Hawking's theory, black holes do emit radiation (and therefore mass) in accordance with quantum rules.  Theoretically, given enough time a black hole could radiate away enough of its mass to disappear completely.  When its mass drops below a certain critical threshhold, the remaining mass of the black hole would disappear in a final violent burst of gamma radiation.  Unfortunately (or perhaps fortunately) the best estimates we have for the time it would take for a black hole to explode in this way is far longer than the current estimated age of the universe, so it is not likely we would be able to test this theory through direct observation.
240841
Small black holes disappear in a puff of Hawking radiation, pretty rapidly.\n\nThey don't really need containment. They just evapourate into thermal radiation.  It's only the dirty great big ones that could smash the place up.  Making one of these on earth is just not feasible.  The ones that occur naturally in the universe are rather a long way off.\n\nNothing to worry about.
4780
Its because physics seems to be really confused about this issue. We're all taught that Gravity is a force of attraction between masses. However, when you look at General Relativity you find that it is not. It is the warping of space-time by mass that causes masses to follow curved geometries that make it look like there is a force acting between them. Where it is really confusing is that then they say that Gravity is transmitted through gravitons - which seems counter intuitive to the whole GR scene. I think that's why Physics is still struggling to find a GUT (Grand Unified Theory) - they are trying to shoe-horn gravity into a place it doesn't belong.
369316
Unknown. Without an adequate theory of quantum gravity, this object that GR predicts would be a singularity cannot be described. At quantum mechanical scales, pure General Relativity is not a realistic depcition of space-time.
319618
well first of all know the actual formula of gravity\nThe standard formula for gravity is: \n\nGravitational force = (G * m1 * m2) / (d2) \nwhere G is the gravitational constant, m1 and m2 are the masses of the two objects for which you are calculating the force, and d is the distance between the centers of gravity of the two masses. \n\nSo gravity depends on the mass and the distance between the two masses\n\nWell the nuclear force is stronger than gravity but the difference is that nuclear force acts over a small distance whereas gravity acts over a longer distance.\n\nIn case of a black hole ,black hole is of immense mass and immense density.It is soo strong that it can even atrract photons.So gravity of a black hole must be a larger force
522977
You can spin a black hole?   Well aren't you talented...  actually the whole known physical universe is first and foremost a gigantic black hole, and it is in motion.  Before the first star formed the dark spacial universe existed and on the smallest scale there is no empty space, everything is connected.  It has been said that darkness is merely the absence of light, but there's no such thing as nothing, everything is made of something, even the ordinary everyday nighttime darkness, on some immeasurable scale even your shadow is made of something?  Black holes are a different more massive type of darkness comprised of dark physical matter.   There's a theory that every galaxy has one at the center and without it the stars that form a galaxy couldn't exist, and it's probable that it is already spinning, nothing is actually sitting still.  It's estimated the output of light from all the stars should be enough to light up the whole universe, but it doesn't.  Then where does it go, what happens to it, we know on a sub atomic scale it doesn't simply dissipate?  Where does the darkness go when you switch on a light?  When you turn off the light, obviously it's still there, so wasn't it there the whole time?   Well, there are still more questions than answers, and maybe you should be a physicist, perhaps you could find an answer to the enigmas of the infinite machine.
230958
I think you asked a very good question. I would like to see someone answer this question correctly as well.\n\nBut just to give you my understanding, which is this: force mediating particles are NOT real particles. They are considered to be virtual particles and thus may not be subject to the same rules as real particles.\n\nThe answer given before me can NOT be true, because the amount of leaking radiation due to the Uncertainty Principle is miniscule. There simply would not be enough gavitons escaping the blackhole and make its presence felt.\n\nJust to give you some numbers:\n\nFor a black hole of one solar mass (about 2x10^30 kg), we get an evaporation time of 10^67 years — much longer than the current age of the universe.\n\nBut even for a black hole of 10^11 kg, the evaporation time is about 3 billion years.\n\nThe power, or engergy output per unit time, in the Hawking radiation from a solar mass black hole turns out to be a minuscule 10−28 watts. Blackholes are black for a reason!!!\n\nOk, here is a definition of virtual particles take directly from Wikipedia:\n\nIn physics, a virtual particle is a particle-like abstraction used in some models of quantum field theory. Virtual particles exhibit some of the phenomena that real particles do such as conservation of charge. Nevertheless they are unobservable by their very definition, and furthermore do not respect some of the most fundamental laws associated with physical particles.\n\nSo force mediators don't obey the same rules as real particles!!!\n\nBy the way, Quantum Field Theory is NOT compatible with General Relativity (our current theory of gravity). Therefore, you are currently trying to reconcile quantum field theory concepts (like force mediators) with extreme gravity (i.e. blackholes), which is a task that the best theoritical physicsts of our time are still struggling with. Superstring Theory and Quantum Gravity are the two top contenders to combine quantum mechanics with G.R. to provide a coherent theory of all forces.\n\nI think we need to consult one of them for the answer.