Gravity. We cannot see or directly detect "dark matter", and the only reason why astronomers talk about "dark matter" is that galaxies like the Milky Way appear to be spinning too fast for gravity to hold them together. Or at least, for the gravity of the mass that we can SEE to hold them together. Gravity comes from matter, and we can't see enough matter, so it must be "dark matter".
This may be in the form of trillions of invisibly-dim brown dwarf stars, or in black holes from which no light ever escapes - or it may be something entirely new. "Dark matter" is the something new.
no actually matter is well matter that we can detect but dark matter is there just we can't detect it but we do no it's there because everything is either matter or engery but we can dectect engery so it's darkmatter
Dark matter and dark energy have NOT been detected yet, so any ideas about detecting dark energy and dark matter, whether it be directly or indirectly, is speculation for now.
Neutrinos are all but impossible to detect and it is thought that they may have mass. If they are found to have mass, they would be the epitome of dark matter.
Dark matter is matter of an unknown type. It is known to exist, due to its gravitational influence, but it is not known what it is made of. There is at least 5 times as much dark matter than "normal" matter.
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Mainly that dark matter interacts with dark matter and with normal matter via the gravitational force; and that it DOES NOT interact with normal matter via any other known force. Or, if there is any interaction, it does so to such a small extent that it hasn't been possible to detect this so far.
Dark matter is sort of a cosmic scaffolding, holding galaxies together through sheer abundance, and since it only interacts with matter gravitationally, you cannot see it, and nor can you detect it....yet.
Mainly that dark matter interacts with dark matter and with normal matter via the gravitational force; and that it DOES NOT interact with normal matter via any other known force. Or, if there is any interaction, it does so to such a small extent that it hasn't been possible to detect this so far.
No. Dark matter emits no EM radiation that we can detect, and we can detect light from galaxies outside the Milky Way over 17 orders of magnitude. Specifically, from radio waves as long as 10 meters to gamma rays of over 1 GeV in energy. Since there is far more gravitational interaction between dark matter and baryonic matter (ie, the stuff we understand) than that occuring between baryons, then it would be truly bizarre that we could not detect any EM radiation coming from dark matter. If it were emitting EM radiation, then we should see more of it than we can see coming from baryonic matter. But we don't see anything. So either dark matter has no EM interaction (ie, no EM radiation) or its EM interaction is so weak and different than that for baryons.
We do not know as we have not found any dark matter to examine. The only way we detect it and know it exists is due to its gravitational attraction of the ordinary matter we can see. One speculation when neutrinos were discovered to have tiny nonzero masses was that dark matter might be neutrinos. Another speculation is that dark matter is only ordinary matter, but its in another separate universe in a shared higher dimensional spacetime. Nobody knows.
Dark matter is sort of a cosmic scaffolding, holding galaxies together through sheer abundance, and since it only interacts with matter gravitationally, you cannot see it, and nor can you detect it....yet.
The clear answer is, we don't. We cannot detect the hypothetical "dark matter", and the only reason we are talking about "dark matter" is that we cannot actually see enough mass in the Milky Way galaxy to account for the gravity that we know must be there - because the Milky Way would fly apart with only the mass that we can see. The "dark matter" may be in the form of invisibly-dim brown dwarf stars, or black holes, or "something else". Dark matter is the "something else". Everything you read about dark matter is a guess.