Questions tagged [dark-matter]

Questions about astrophysical observations, experimental searches, and theoretical models related to dark matter and its quanta.

The astrophysical dark matter outweighs our usual ("baryonic") matter 5:1. There is a wealth of independent cosmological and astrophysical observations that all support this conclusion; the most important examples are

The nature of dark matter is unknown, and significant experimental effort is devoted to identifying the quanta of dark matter. Most notably, this includes

  • precision gravitational observations of astrophysical systems
  • so-called "indirect" astronomical searches for dark matter annihilation or decay products
  • searches at colliders for particles that might be related to dark matter and
  • the so-called "direct" searches for scattering or other interactions of dark matter with laboratory-scale experiments.

Notable hypotheses for dark matter quanta include Axions, WIMPs, and sterile neutrinos. Questions related to these observations, experimental methods, or theoretical models should be tagged with tag.

948 questions
94
votes
7 answers

If dark matter only interacts with gravity, why doesn't it all clump together in a single point?

I'm a complete layperson. As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, strong nuclear force, and electromagnetism. Those are…
56
votes
4 answers

Are modified theories of gravity credible?

I'm a statistician with a little training in physics and would just like to know the general consensus on a few things. I'm reading a book by John Moffat which basically tries to state how GR makes failed predictions in certain situations. I know GR…
56
votes
1 answer

What is the upper-limit on intrinsic heating due to dark matter?

Cold dark matter is thought to fill our galactic neighborhood with a density $\rho$ of about 0.3 GeV/cm${}^3$ and with a velocity $v$ of roughly 200 to 300 km/s. (The velocity dispersion is much debated.) For a given dark matter mass $m$ and…
54
votes
4 answers

How do we know Dark Matter isn't simply Neutrinos?

What evidence is there that dark matter isn't one of the known types of neutrinos? If it were, how would this be measurable?
ripper234
  • 705
  • 2
  • 6
  • 8
51
votes
3 answers

Why do physicists assume that dark matter is weakly interacting?

IceCube, XENON, etc, keep yielding negative results. If dark matter exists, it doesn't interact with baryonic matter at the energy ranges they can detect. The response is to build even bigger detectors to search for even fainter energy…
Foo Bar
  • 1,000
51
votes
8 answers

Why isn't dark matter just ordinary matter?

There's more gravitational force in our galaxy (and others) than can be explained by counting stars made of ordinary matter. So why not lots of dark planetary systems (i.e., without stars) made of ordinary matter? Why must we assume some…
39
votes
1 answer

How can dark matter collapse without collisions or radiation?

I understand that dark matter does not collapse into dense objects like stars apparently because it is non-interacting or radiating and thus cannot lose energy as it collapses. However why then does it form galactic halos? Isn't that also an example…
Astrobuf
  • 391
  • 2
  • 3
38
votes
1 answer

Is there any evidence that dark matter interacts with ordinary matter non-gravitationally?

As far as I understand it, dark matter direct detection experiments are based on the idea that dark matter interacts with ordinary matter, it just has a very small cross-section. So far, there's been no confirmed detection. Is there any evidence at…
33
votes
3 answers

Can the Sun capture dark matter gravitationally?

I think my title sums it up. Given that we think the dark matter is pseudo-spherically distributed and orbits in the Galactic potential with everything else, then I assume that its speed with respect to the Sun will have a distribution with an rms…
ProfRob
  • 141,325
32
votes
3 answers

Is Dark Matter called "Matter" only because of gravity?

As far as my understanding goes, dark matter is nothing but an amount of gravitational force, from yet unresolved/undiscovered source(s), needed to explain some observed attributes of our universe. Then, is it called "Matter" only because of…
Gulshan
  • 713
31
votes
5 answers

Why doesn't dark matter affect planetary motion?

If the universe is made up of ~95% dark matter, and it interacts only gravitationally then why didn't Newton and Kepler discover it before ? Why does it show itself only in the radial velocity profile of stars in galaxies and not in that of planets…
user44330
  • 311
30
votes
1 answer

Why is Anti-helium so important in the search for dark matter?

I've been reading/hearing that if the AMS satellite measures a significant flux of anti-helium in cosmic rays, that would be an irrefutable proof of dark matter. I was wondering: Why is that? what is the dark matter decay/annihilation that produces…
Juanjo
  • 930
  • 7
  • 18
29
votes
3 answers

How do people calculate proportions of dark matter, dark energy and baryonic matter of the universe?

The Wikipedia page on dark matter mentions that the Planck mission had revealed that in our universe ordinary baryonic matter, dark matter and dark energy are present in the ratio: 4.9%, 26.8% and 68.3% respectively. I do not understand exactly how…
28
votes
4 answers

How did the universe shift from "dark matter dominated" to "dark energy dominated"?

In order to get dark energy to dominate, wouldn't you first need another form of energy to push the expansion until dark energy could dominate? Otherwise I don't understand how the universe could shift from having a decelerating expansion to an…
25
votes
6 answers

Why can't dark matter be black holes?

Since 90 % of matter is what we cannot see, why can't it be black-holes from early on? Is is possible to figure out that there are no black holes in the line of sight of various stars/galaxies we observe?
Jus12
  • 3,463
  • 4
  • 25
  • 30
1
2 3
62 63