Can dark matter be black holes?
546765
Greetings,\n\nDark matter doesn't have to be dark.  It's called dark matter because we don't know what it is.\n\nCurrent cosmological theories regarding the expansion of the universe and accelleration of that expansion tell us there is matter and energy we have not accounted for or discovered yet.\n\nBlack holes fall into matter we have, for the most part, accounted for.\n\n-matt
697469
it can be. Because blackhole has a much faster velocity than light. It is possible that we can use blackhole to travel into another galaxy or another space that we haven't know before. Or maybe we can use blackhole as a time machine. Everything can happen, one day we can find it out. I believe that
1081457
No.  Light can orbit inside a black hole right below the event horizon provided it's trajectory was perfect when entering the black hole. If not the light always head towards the singularity. Yes light is attracted to a black hole due to the complete and absolute curvature of space time located there. Light does not need mass, it just follows the curvature of space-time into the black hole.
13556
There are theoretically two ways in which black holes can form.  Stellar (star) sized black holes have to be above the Chandresekhar limit of 3.2 solar masses, and are formed through the gravitational collapse of stars. They can form whenever conditions are right. These are the types of black holes that astronomers infer from binary X-ray sources and the like.\n\nMicro black holes, on the other hand, can only have been formed in the initial moments of the Big Bang, when intense pressures during cosmic expansion could have collapsed masses smaller than our sun into singularities.  According to Dr. Stephen Hawking's theory of black hole evaporation, all singularities lose mass, through a type of evaporation (the actual mechanism, having to do with vaccum energy and particle/antiparticle pairs is a bit complicated) with smaller black holes evaporating faster than large ones.  By this logic, most micro-holes would have evaporated out of existence in the thirteen billion years the universe has been around, while the larger micro-holes (things with the mass of, say, Neptune) should still be around, though hard to spot.
274083
No.  A black hole is an immensely dense object, like taking all the matter in our solar system plus more, and condensing it to the size of a pea or so.  The moment we could "create" one, the entire earth would be "sucked into" it.
72214
Black holes almost certainly exist. Wormholes almost certainly do not.
755373
Black holes are a concept in cosmology and theoretical physics.  The idea of going into one doesn't really fit in with the science. \n\nUsing a mechanical model of the universe, black holes are extremely dense concentrations of matter with such a high gravitational force that everything (including light) is sucked in and cannot escape.  If you went near a black hole, you would be broken down into subatomic particles and crammed into the lump of compressed matter at the centre.\n\nHowever, quantum physics gives an alternative theory.  Black holes could be the ways in and out of shortcuts across the universe so that something sucked into one could be spat out of another.  This is probably something best not tried at home.
1150780
In fact, there is a great deal of evidence showing it is not. What little we know of the dark matter and energy is that they are not composed of baryons. But anti-protons *are* bosons. There are some candidates for the dark matter (axions are a good bet) but anti-matter in the usual sense is ruled out by observation.
1021193
No idea what you mean by your comment.....\n\nIn cosmology, dark matter refers to matter  of yet unknown composition, that does not emit or reflect enough light to be detected directly. But its presence may be inferred from gravitational effects on visible matter such as stars and galaxies. \n\nEvidence suggest that there is much more dark matter than visible matter. As it is non-interacting with light it must be of non-baryonic origin. It also must be stable, because it exists since the Big Bang, 14 billion years ago. The only candidate among the elementary particles we know already are the neutrinos. However there are theories like Supersymmetry that predict other particles, that would fit the known data.
1095953
There are no black holes close enough for a terrestrial probe to reach them yet. According to current theory, the intense gravitational field would trap any electromagnetic signal the probe might be sending out after it crossed the event horizon, so we wouldn't know what happened in any event.
28506
A black whole is the closest to infinite density of mass that could be feasable given the dementions that we currently live in\n\nTry this:\nhttp://en.wikipedia.org/wiki/Blackhole
1136303
A black hole is not actually a hole, but a physical object in space, consisting of ultra compact particals, contained in such a small area that thier gravitational pull is much stronger than any other celestial body of comperable size....  Basically you put all the matter and gravitational pull from a large star into the volume of a small moon... particles captured by a black hole are crushed and added to its composition. This in theory includes photons (light and other energy)as well.  As for whether black holes are hoax's or not.. the answer is no... we can see their effects on star near them, including gases that are syphoned, and other gravitational interactions.  Additionally when matter approaches a black hole and is accellerated, it reaches an energy level at the even horizon where xrays are emited, but not captured, which in turn we can also detect.  Though there is much we do not know about them, they definately exist, and most likely in much greater numbers than we oringinally thought.
128460
It might be, or it might be a neutron star. We do not really know. \n\nThere are some other objects in the sky which are much more certainly black holes, from their masses and other properties.
230733
In cosmology, dark matter refers to hypothetical matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. The dark matter hypothesis aims to explain several anomalous astronomical observations, such as anomalies in the rotational speed of galaxies (the galaxy rotation problem). Estimates of the amount of matter present in galaxies, based on gravitational effects, consistently suggest that there is far more matter than is directly observable. The existence of dark matter would also resolve a number of inconsistencies in the Big Bang theory, and is crucial for structure formation.\n\nIf dark matter does exist, it has vastly more mass than the "visible" part of the universe. Only about 4% of the total mass in the universe (as inferred from gravitational effects) can be seen directly. About 23% is thought to be composed of dark matter. The remaining 73% is thought to consist of dark energy, an even stranger component, distributed diffusely in space, that probably cannot be thought of as ordinary particles. Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics.
1057606
Most people *don't* believe galaxies are black holes.  A black hole is a region of space from which nothing can escape, even light.  \n\nSince you can't see a black hole (that light that isn't escaping), one has to rely on indirect evidence.  \n\n If you've found a large mass concentrated in a small volume, and if the mass is dark, then it's a good guess that there's a black hole there.  \n\nIt'll be quite some time before we can get "hard evidence" of a black hole.  We don't even have "hard evidence" that those are stars; it's just indirect evidence.
387898
Black holes are food for my brain and curiosity. I love the subject it is so interesting!\nBackround info: A black hole is a concentration of mass great enough that the force of gravity prevents anything from escaping from it except through quantum tunneling behavior. The gravitational field is so strong that the escape velocity near it exceeds the speed of light. This implies that nothing, not even light, can escape its gravity, hence the word "black." The term "black hole" is widespread, even though it does not refer to a hole in the usual sense, but rather a region of space from which nothing can return. Theoretically, black holes can have any size, from microscopic to near the size of the observable universe.\nBlack holes are predicted by general relativity. According to classical general relativity, neither matter nor information can flow from the interior of a black hole to an outside observer. For example, one cannot bring out any of its mass, or receive a reflection back by shining a light source such as a flashlight, or retrieve any information about the material that has entered the black hole. Quantum mechanical effects may allow matter and energy to radiate from black holes; however, it is thought that the nature of the radiation does not depend on what has fallen into the black hole in the past.\n\nThe existence of black holes in the universe is well supported by astronomical observation, particularly from studying supernovae and X-ray emissions from active galactic nuclei.\nMy answer 1)time travel when you, or in this case an object, goes fast the world goes slow. and if something, a black hole, is going, or sucking, fast enough, the world around you will eventually begin to reverse.
1122271
A black hole does not necessarily pull in everything in the universe. It's gravitational field is no different from any other object of the same mass, until you get very close.\n\nAccording to Stephen Hawking, black holes will evaporate over time. However, a black hole the mass of the Sun would take many times the current age of the universe to disappear. So the billion-solar-mass black holes at the centers of giant elliptical galaxies will probably still be around when everything in the universe has gone cold.