I have always heard about dark matter, but I do not know what it means, what its uses are, and does it really exist?
In: Chemistry
If you swing something at the end of a rope in a circle, you will feel that you need to pull to keep it from flying of. The faster you swing it, the harder you need to pull.
When looking at distant galaxies we can do the opposite, look at how fast the stars move to figure out how strongly they are held.
Unless we have completely misunderstod physics, they are held by the mass of the galaxy further inward. We have a decent understanding of stars, so we know how heavy the stars are, and they are not heavy to explain the motions we observe. One possible explanation is that there is more mass, that does not emit light: dark matter.
Exactly what this dark matter is is not known. Some of may be perfectly normal matter, but too cold to emit light.
dark matter is like invisible glue that holds galaxys together. we cant see it or touch it, but scientist think its there because of how stars and galaxys move. imagine spining a bucket of water – the water stays inside becuz of the buckets walls. in space, stars spin around galaxys real fast, but they dont fly away. scientists think dark matter acts like a invisible bucket, keeping everything in place with it’s gravity. we dont know exactly what dark matter is made of yet though
“Dark Matter” is a kind of misleading name because it doesn’t describe a substance that we have directly observed and described. Rather, it’s a name that describes some cosmological observations that we have made. There are several different theories of dark matter, but the most popular one is that it’s just a type of matter that we can’t see, hence the name
To go into more detail the dynamics of observable galaxies suggest that they have more mass in them than could exist in all the stars that we can see. If gravity works the way we think it works, and it works the same way in all galaxies, and most of the mass in galaxies is in stars and black holes and other stuff we can observe, then something doesn’t add up. You might say well then, maybe gravity just doesn’t work the way we thought it does – that is a theory of dark matter called ‘mond’ for ‘modified Newtonian dynamics.’ The biggest problem with that theory though is that different galaxies appear to have different amounts of missing mass, which doesn’t really work with the mond idea. A more popular theory is called ‘CDM’ – cold dark matter – which just basically says dark matter is a kind of exotic particle that doesn’t interact with electromagnetism, so we can’t see it, but does interact with gravity, so it has mass, and generally moves around slowly (i.e., it’s cold).
As for uses of dark matter, well, we don’t know. But I would guess that we aren’t likely to find any any time soon. If the theory that dark matter doesn’t interact with electromagnetism is correct, then dark matter is not only dark, it can never form any molecules or compounds. Not only that, but it wouldn’t collide with normal matter in the expected way, because that mostly happens via electromagnetism. You could be surrounded by dark matter right now and be none the wiser; it would just be completely inert and invisible as far as we’re concerned
ELI5: We have noticed that shit spins a lot faster than it should with how much mass we see and what physics of gravity tells us. .
So we formed two hypotheses, one is that our laws are wrong, this one has not so much support and doesn’t seem to work too well. The second is that there’s a lot more mass than we can see, and this mass is “dark” matter. We have no idea what this could possibly be and there has been no direct evidence for it.
There’s no direct evidence for dark matter.
What we currently know about the matter constituting the universe (stars, nebulae, planets, etc. ) accounts only for about 15% of what should be required to explain the phenomena we observe (like [formation and evolution of galaxies](https://en.wikipedia.org/wiki/Galaxy_formation_and_evolution), [gravitational lensing](https://en.wikipedia.org/wiki/Gravitational_lensing), the [observable universe](https://en.wikipedia.org/wiki/Observable_universe)’s current structure, the motion of galaxies within [galaxy clusters](https://en.wikipedia.org/wiki/Galaxy_cluster), etc.). The remaining 85% are called “dark matter” (because we can’t observe it) until a better explanation is found.
Galaxies spin faster than they should, according to our understanding of gravity. This means either we don’t properly understand gravity on that large scale, or there is more mass making up galaxies than we can see. That extra mass is what we call dark matter.
We have not made any direct observations of dark matter, but we do know that galaxies are spinning as if they have more mass than there appears to be.
The answer is no.
“Dark matter” is a placeholder name for what appears to be causing extra gravity in space. As far as we know, only matter can cause gravity, but there is no matter to be seen.
Why this extra gravity exists is not known. There is no direct evidence or proof for whatever is causing it. There are many theories and experiments to try to support these theories have been conducted, but so far, no experiment has delivered results.
To my understanding it’s not so much a substance as a theoretical explanation for why stars don’t always seem to behave the way they should, given our understanding of physics.
When reality doesn’t conform to your theory, the possible explanations are that your theory is wrong, or that there’s some unknown variable that accounts for the discrepancy. In this case, if the theory is wrong, then why does it seem to predict so many other things accurately? So the (proposed) unknown variable is lots of extra matter that for some reason we can’t see, thus labeling it “dark.”
Dark matter is invisible and doesn’t interact with light or radiation, but scientists believe it exists because of its gravitational effects on galaxies and the universe. For example, stars on the edges of galaxies rotate faster than they should, indicating unseen mass. Phenomena like gravitational lensing and cosmic background radiation also support the idea of dark matter. While it hasn’t been directly observed, strong evidence of its existence comes from its gravitational effects.
Good evidence comes from galaxy cluster collisions.
We can see huge amounts of matter (gas) that has collided and forms big shock cone structures, and we can also see where the mass is due to gravitational lensing.
We’d expect the mass to be in the same place as the matter, but instead most of the mass seems to have just carried on going and just passed through each other as if they were ghosts.
[Hence the idea for dark matter](https://www.youtube.com/watch?v=6itfq4CzxZ8) as some form of matter that has mass but doesn’t interact with normal matter or itself except by gravity.
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