Where has all the dark matter gone? Has it disappeared down all those black holes? Does it really exist?
955030
The dark matter hasn't gone anywhere.  The problem is we can't see it directly because it doesn't or reflect any light (hence the name!).  It is defninitely there, but we don't know what form it takes - is it normal matter that just happens to be really really dark (dark dust, very faint brown dwarfs, isolated black holes)?  Or is it some form of weird, exotic matter that we have yet to discover (I know that sounds far-fetched on the surface, but it actually isn't).\n\nWe suspect that dark matter exists for various reasons.  One is by observing how spiral galaxies rotate.  By watching any object orbit around another (like our Sun or other stars orbiting around the center of our galaxy) we can calculate the mass of the thing being orbitted.  But with all spiral galaxies (and others, too) the mass we calculate is far greater than the mass of all the stuff (stars, gas, dust) that we can see - therefore there must be stuff in our galaxy that we can't see, but that still has a significant gravitational effect.\n\nWe also see galaxies orbiting each other.  Here again, but watching them we can calculate how much mass there is, since mass determines gravity.  If we only had the mass of the visible stuff inside and outside the galaxies, those galaxy clusters should break apart - the gravitational force from all the visible stuff isn't strong enough to hold those clusters together.  But those clusters do stay together, so there must be more dark matter there between the galaxies.\n\nNow you may just be asking yourself "maybe gravity doesn't work the same on the galactic scale as it does here on Earth", which is a question scientists have asked, as well.  But recent evidence suggests that that is not the case - that we really do need dark matter to explain our observations.\n\nIt gets even weirder - we now think there's something called "dark energy" that is causing our Universe to epand at a faster rate, instead of being slowed down by gravity the way we used to expect.\n\nThere are quite a few good books about this stuff written for laymen - just puruse your local book store in the science section.  And if it all seems too confusing, don't worry - it's confusing to the scientists, too!  As I tell my students, if it all seems to make sense, you're not paying attention!
590743
The most interesting fact I know?  That they don't exist and that they're some stupid idea somebody came up with to help explain a few things we don't currently understand.  Singularities have infinitely dense mass?  Riiiight.\n\nYou'd better start reading up on the Electric Universe, buddy.  There are powerful magnetic fields all over the Universe, and the stupid idiot "scientists" running the show right now don't like to acknowledge that maybe there are electric currents shaping our galaxies.
277935
A galaxy is a huge gravitationally bound system of stars, interstellar gas and dust, plasma, and (possibly) unseen dark matter. Typical galaxies contain 10 million to one trillion (107 to 1012) stars, all orbiting a common center of gravity. In addition to single stars and a tenuous interstellar medium, most galaxies contain a large number of multiple star systems and star clusters as well as various types of nebulae. Most galaxies are several thousand to several hundred thousand light years in diameter and are usually separated from one another by distances on the order of millions of light years.\n\nAlthough so-called dark matter appears to account around 90% of the mass of most galaxies, the nature of this unseen components is not well understood. There is some evidence that supermassive black holes may exist at the center of many, if not all, galaxies.\n\nIntergalactic space, the space between galaxies, is filled with a tenuous plasma with an average density less than one atom per cubic meter. There are probably more than a hundred billion (1011) galaxies in the visible universe.
486232
The universe is theorized to contain dark energy and dark matter. There have been some confirmation of it's existence but really just speculation at this point. The idea of dark matter had been identified by Einstein but it wasn't till the discovery that the universe is accelerating it's expansion and contains up to 70% more matter that the idea of dark matter and energy became serious areas of study. If you mean a vacuum to mean absence of air it is a vacuum but within that "vacuum" there definitely is matter.
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.
936416
you should see the nova on blackholes, it was on last week\n\napprently only to much can actually get to the center at a time, and most matter/energy gets bounced around within the event horizon, never to escape, but not actually getting all the way in\n\nand anyway blackhole emit particles of hawking radiation and would eventually expell there mass and kinda evaporate away\n\nand if one black hole had the whole universe in it, sounds prime for  big bang to me
924845
Interesting.  Since muons, even at near-light speed, are likely to decay before hitting Earth-local detectors, it seems difficult to believe that any have been detected.  At least I've seen no articles on muon radiation from black holes in the major science publications.\n\nAlso, if you were indeed a walking black hole, the circumference of your event horizon would probably be comparable to the size of a proton or maybe smaller.  In which case, you wouldn't really be walking or typing or reading this answer.  <sigh>.\n\nAnd we even shouldn't go anywhere near considering the effects of stellar-equivalent energy flux around your navel.  Does the term "massively extra crispy" begin to communicate the state of your body not to mention your surrounding area for miles?  Thought so.
261254
Dark matter refers to hypothetical matter particles that cannot be seen or observed because it does not emit or reflect enough electromagnetic radiation.  Since there have been the missing mass problem and the problem dealing with stars at the edge of the galaxy moving at about the same speed as stars near the centre rather than being like our Solar System where planets and other objects far from the Sun revolve around the Sun slower while objects closer to the Sun revolve faster due to higher escape velocities.  \n\nNo, we're not dark matter.\n\n22% of the mass is dark matter, while only 4% of the mass is observable matter, and the remaining 74% is thought to be dark energy, something even stranger.
967381
new research show that galaxies are held together by dark matter which until recently there was little or no evidence of,however i believe the massiveness of the entire universe is actually exerting pressure ever so slightly upon the galaxies and that force is squeezing them upon a tightly wound black hole which appears to be a gravitational force, but i compare it to all the water in a tub pressing itself gently into a whirlpool as it goes down the drain...yes it is gravity pulling it down the drain but if that same whirlpool was in space it would have more similarities to a black hole
943076
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.
568018
Dark matter is actual matter in the sense that it has mass.  But it doesn't seem to absorb or reflect electromagnetic radiation, hence the term 'dark' matter.  Of course, this is all based on the assumption that dark matter actually exists.  It's really just a theory.  From what I've read, no one seems to have direct evidence that it exists.
447237
Dark matter provides the gravitational force that prevents galaxies being ripped apart by their angular momentum.  We have no way of detecting it, except from the bending of light around it.
1094849
setting aside the philosophical issues and taking this question strictly within scientific contexts, probably one of the hardest questions, if not the hardest yet, is related to the question of whether the universe as we know it would forever expand till the end of time (because we know right now that it is expanding), or will everything's mass and gravitational pull would be quite enough to "pull" everything back at some point in time such that the Big Bang sort of reverses itself (the current scientific paradigm agrees with the Big Bang theory).\n\nthe catch here isn't in the question of the forever-expansion or the eventual "Big Crunch" of the universe, but of where to find all the mass that is in question (remember, with enough mass, the Big Crunch will ensue). problem is, if i'm not mistaken, if we adhere to Einstein's Relativity (which we do), there isn't even enough DETECTED mass in the universe to actually hold itself together. at the quantity of mass scientists have been able to confirm, the universe should be chaotic, instead of peaceful and following an orderly behavior. without enough mass, there wouldn't be enough gravitational pull to hold the heavenly bodies steady in their "places", whatever they may be doing.\n\nthe true hard question here is actually: "what makes up the missing mass?", because as we can see, the universe is itself NOT chaotic and not falling into pieces or something. this would mean that there actually is something in the universe (or in space) that has mass that we cannot yet see or detect, and that there's enough of it to hold the universe together. scientists have referred to this "missing matter" as "dark matter", since we cannot yet see or detect it, but we somehow know its there. as far as i know, scientists haven't been able to pinpoint what dark matter actually is.
260891
Well, people have been spotting and reporting MACHOs for a long time, simply by how they affect light that passes through them.\n\nI believe that WIMPs, if they exist, would be the source for more of the energy density requirements to keep omega at ~1. MACHOs only exist within galactic halos, and are aggregated. WIMPs, on the other hand, are likely to be evenly distriubuted within and between galaxies, acounting for their rotation and their movements relative to one another. I think the lack of information about WIMPs is simply due to the limits of our technology in being able to detect particles that only respond to gravitational fields and require a lot of energy to make because they are heavy. If a particle does not interact with any force at all except gravity, it is likely to be a long time before we ever prove that it exists.\n\nI also think that the fermionic superpartner to the Higgs boson is a good candidate for the WIMP, and it is likely that the debate on the existence of supersymmetric particles will be put to rest as soon as those giant particle accelerators are built in Europe. I think the one is supposed to be online in 2008.
21830
"Dark" is not produced, per se...but it is an absence of light.  A black hole absorbs light...perhaps that is what you are looking for...\n\nLook at this website...it provides a quick overview of black holes and how they are created: \nhttp://www.damtp.cam.ac.uk/user/gr/public/bh_home.html\n\nAlso...to the person below me here...the clouds do not absorb light.  They block the sun's light and reflect it back to the atmosphere therefor cutting it off from our view.  However, some of the rays that come from the sun travel through the clouds, such as UV rays.  If the clouds absorbed light, we would see nothing during an overcast day.
473304
This is a very intriguing question which I plan on researching. I have a conception of light and its physical properties and also the tremendous mysteries of a 'Black Hole'Where current day Physics is just beginning to grasp.NOTHING escapes the gravity of a 'Black Hole',not even light!Through the efforts  of dilligent astronomers, one was actually 'seen' and filmed as it passed in front of a known group of stars...outlining the very hole itself.(like passing an object in front of a bright light source and observing the outline of the object...i.e. Solar eclipse...,) knowing of there existence and how to track them now ,has given a whole new meaning to the destructive forces of a 'Black Hole' as it swallows up Stars, that Dwarf our Sun in comparrison,and the Solar System it may support.This is Truly Dark Matter on the 'Anti' side...Anti-matter...a Black Hole is given birth by a Star,such as our Sun, that is dying.As this Star,once a source of Light that supported a probable solar system, goes through its Final death throws it eventually explodes, but it just doesnt explode! as its  surface layers are  blasted outwards, its  core is smashed inwards. The center of the star  collapses in on itself. Billions upon Billions of tons of Star stuff crushed smaller and smaller until the whole Star is squeezed to a microscopic point,and from the remains of the dying Star, ....a BLACK HOLE is born....in our Galaxy,the Milky Way, a Massive Star explodes and creates another black hole every 1000 years. There is a estimated 10 Million Black Holes roaming our Glaxy today, creating Havoc sucking matter in around them... NOTHING escapes! As we know, anything of SUBSTANCE has mass, microscopic as well as Galatic.Once realized that the incredible forces hatched by a black hole having the ability to bend light and distort the Space/Time continuum which in itself is invisible to the eye, is it a possibility that this very same process is taking place at a molecular level? If manipulated correctly, is 'Cloaking' a possibility? your Question is very intriguing indeed!
575553
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.