Questions tagged [dark-matter]

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

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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 ...
Andrew Beatty's user avatar
54 votes
4 answers
13k views

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's user avatar
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53 votes
3 answers
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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 ...
dcl's user avatar
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92 votes
7 answers
13k views

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, ...
user151841's user avatar
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28 votes
4 answers
6k views

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 ...
user43783's user avatar
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38 votes
1 answer
2k views

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 ...
Astrobuf's user avatar
  • 381
25 votes
6 answers
7k views

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 ...
Jus12's user avatar
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22 votes
2 answers
3k views

Why are neutrinos ruled out as a major (or even sole) component of dark matter?

A number of times I have encountered in text-books and articles that neutrinos might contribute only a small fraction to dark matter. The reason has to do with the fact that if all of the dark matter ...
ThisGuy's user avatar
  • 547
31 votes
5 answers
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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 ...
user44330's user avatar
  • 311
7 votes
4 answers
1k views

Theory that gets rid of dark matter/energy

Is there any physics theory that either groups together gravity and dark energy/dark matter or eliminates dark energy/dark matter by modifying standard understanding of gravity or any force? If so, is ...
Albert Schewartz's user avatar
3 votes
2 answers
480 views

How does the friedmon solution to Einstein's equations resolve paradox of bounded infinities?

This article talks about a potential explanation of dark matter based on something called the "friedmon." I have no interest in the dark matter question, but the article has made me curious about ...
ben's user avatar
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19 votes
5 answers
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Dark matter and dark energy references

I've been looking for questions about dark matter, and I've read some very interesting answers. However, I desire too look into it deeply. This is not actually a question. I'm asking the community ...
8 votes
2 answers
270 views

Are there experiments taking place right now that might show evidence for or falsify dark energy or dark matter?

What experiments at quantum or cosmic level might provide the strongest supporting evidence for or, conversely, potential for falsifying, the existence of dark matter or dark energy?
OC2012's user avatar
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8 votes
2 answers
1k views

How does dark matter halo outside a galaxy help to explain galaxy rotation curve?

How does a dark matter halo outside a galaxy help to explain a galaxy rotation curve? Suppose for simplicity we use a model of a star rotating about a more massive star in a fixed circular orbit. For ...
curious's user avatar
  • 1,057
12 votes
2 answers
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Could Dark Matter form black hole?

Some people speculate that the mysterious dark matter in the universe could be tiny black holes. But on the other side, could dark matter particles attract each other by gravity and finally form a ...
Fine Observer's user avatar
8 votes
2 answers
641 views

Has frame dragging been accounted for in galactic rotation curves?

This article explicitly takes frame dragging into account in calculating expected galactic rotation curves in the absence of dark matter, and appears to obtain very close matches to observed curves. ...
S. McGrew's user avatar
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2 votes
2 answers
2k views

Why can't dark matter be baryonic? [duplicate]

Here's what I know about dark matter: Astrophysicists realized the movements of galaxies and other astronomical bodies cannot be explained by the gravitational effects of matter known to be there, so ...
Jmfig314's user avatar
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1 vote
2 answers
417 views

Possibility of making dark energy equivalent with dark matter

I was curious whether it is possible to make dark energy equivalent to dark matter. Can this unification be done? If it can, why do scientists prefer to separate dark energy from dark matter?
quantum beginner's user avatar
1 vote
2 answers
625 views

Relativity and Galaxy Rotation Speed

If time travels slower nearer gravity wells, why can't the galaxy rotation speeds being faster on the outer edges than the inner areas be explained by relativity? What necessitates dark matter?
ahnbizcad's user avatar
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29 votes
3 answers
9k views

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....
curious's user avatar
  • 1,057
18 votes
1 answer
700 views

Distribution of Dark Matter around galaxies [duplicate]

It is well-known that measurements of the velocity profile in galaxies are not compatible with Newtonian laws. A way to circumvent the problem is to assume that galaxies are surrounded by a spherical ...
Christophe's user avatar
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12 votes
5 answers
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Is Dark Matter expected to be equally distributed in our solar system?

If dark matter winds up being roughly equally distributed in our solar system would this mean it has no net gravitational influence? Furthermore, do we expect dark matter to be less dense out in ...
Alex's user avatar
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9 votes
7 answers
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How do we know that dark matter is dark?

How do we know that dark matter is dark, in the sense that it doesn't give out any light or absorb any? It is impossible for humans to be watching every single wavelength. For example, what about ...
Jonathan.'s user avatar
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8 votes
1 answer
575 views

Why doesn't the dark matter halo co-rotate with the luminous disk? What keeps it from falling into the center if not angular momentum?

Why doesn't the dark matter halo co-rotate with the luminous disk? What keeps it from falling into the center if not angular momentum?
Disputationist's user avatar
3 votes
2 answers
1k views

Dark matter and dark energy [duplicate]

Possible Duplicate: Dark matter references I have recently read about dark matter and dark energy, and why physicists think it must exist (dark matter: mass of galaxies are far bigger than ...
user14445's user avatar
  • 1,483
32 votes
3 answers
5k views

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. ...
Gulshan's user avatar
  • 703
23 votes
1 answer
9k views

How do we know Dark Matter is non-baryonic? [duplicate]

It seems widely stated, but not thoroughly explained, that Dark Matter is not normal matter as we understand it. Wikipedia states "Consistency with other observations indicates that the vast majority ...
Ehryk's user avatar
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19 votes
2 answers
2k views

Is there evidence of dark matter in our galaxy?

Is there evidence of dark matter in our galaxy? How can we measure this, say, how many percent of the center of our galaxy is dark matter? I did not find the answer in the question What's dark ...
Arpad Horvath's user avatar
13 votes
5 answers
827 views

How Does Dark Matter Form Lumps?

As far as we know, the particles of dark matter can interact with each other only by gravitation. No electromagnetics, no weak force, no strong force. So, let's suppose a local slight concentration ...
Michael Luciuk's user avatar
10 votes
2 answers
1k views

Dark Matter vs Modified Gravity

Why do cosmologists and astrophysicists assume that the reason for the higher velocities of outer stars in galaxies is due to matter at all? The name dark matter seems misleading. Couldn't gravity ...
Noon36's user avatar
  • 168
7 votes
2 answers
777 views

Is dark matter really present around the sun?

Recently I read an article that there is dark matter around the sun but if it is so, than why can we see it clearly. If it is called matter than it shall show some hindrance in radiation we receive ...
Pankaj Sejwal's user avatar
7 votes
3 answers
745 views

Dark Matter 'Stars'

I'm aware that the Milky Way has a dark matter 'halo' around it, presumably a spherically symmetric distribution. But I'm completely ignorant regarding the theories explaining dark matter... Is there ...
Kitchi's user avatar
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5 votes
2 answers
259 views

can we have a parallel earth made of dark matter?

In the sense that the two planets move together and has intelligent beings with their own forces and particles, but they just do not interact with (are invisible to) us?
user avatar
21 votes
2 answers
2k views

Could Hawking radiation have a lot of neutrinos and dark matter?

Up till now I have thought that Hawking radiation would be mostly photons, since the temperatures are typically small. However, a comment on another question (thanks to John Doty) suggested that we ...
Andrew Steane's user avatar
20 votes
3 answers
1k views

Why hasn't warm dark matter replaced cold dark matter as the standard model of cosmology?

The $\Lambda\rm CDM$ (cold dark matter with cosmological constant) is the current standard model of cosmology because the model comes with a long list of phenomena successfully explained by it. ...
Kyle Oman's user avatar
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19 votes
3 answers
3k views

Is the term 'matter' in 'dark matter' misleading? [closed]

If the only evidence for dark matter we have is gravitational, why call it 'matter' rather than 'observed space-time geometry that does not match predictions'? General Relativity tells us that mass ...
AlternativelyBaryonic's user avatar
14 votes
3 answers
5k views

How did we 'discover' dark matter? [closed]

I'm an astrophysics student and I've been researching this topic and there is one point that keeps eluding me. How did the scientific community realize that there had to be dark matter in the ...
ManoTech's user avatar
  • 508
14 votes
2 answers
1k views

What is a reasonably accurate but simple model of the Milky Way's gravitational field?

I am putting together a toy program which shows how stars move around in the galaxy. To run the simulation I need to know strength of the Milky Way's gravitational field at any location in it. I'm ...
spraff's user avatar
  • 4,886
11 votes
2 answers
2k views

Mass density of dark matter in solar system near us

What is the approximate mass density of dark matter in our solar system at the radius of the Earth's orbit? I would like some idea of the mass of dark matter going through each cubic meter of ...
John Eastmond's user avatar
10 votes
2 answers
496 views

If neutrinos are disfavoured as DM candidates why aren't axions?

Numerical simulations of observed large-scale structure formation work best with Cold Dark Matter (CDM; see the answer here). Neutrinos are candidates for Hot Dark Matter (HDM), and hence they cannot ...
SRS's user avatar
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9 votes
6 answers
5k views

Why can't "missing mass" (=dark matter) be photons?

After a star lives and dies, I assume virtually all of its mass would be photons. If enough stars have already lived and died, couldn’t there be enough photon energy out there to account for all ...
Tom Fangrow's user avatar
8 votes
3 answers
1k views

Is dark matter really matter?

Is dark matter really a form of matter? We know it has a gravitional attraction and we know that everything that has a gravitional force is made by matter. But maybe this is an exception? And if ...
Rox's user avatar
  • 261
8 votes
1 answer
2k views

Why do physicists think that the dark matter is cold?

Most of the dark matter in the Universe is cold or nonrelativistic which rules out neutrinos as dark matter candidate as they are hot or relativistic. But why do physicists think that the dark matter ...
SRS's user avatar
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7 votes
1 answer
2k views

What fraction of baryonic matter is in stars?

We know from big bang nucleosynthesis that baryonic matter accounts for about 5% of the universe's total mass-energy density. What is the current best estimate of how much of this is in the form of ...
user avatar
6 votes
1 answer
521 views

Does the bullet cluster prove that dark matter must consist of particles?

Some time ago the remnants of a collision between two galaxy clusters were (accidentally) discovered. These remnants are called the bullet cluster. There are some theories around to explain the ...
Deschele Schilder's user avatar
6 votes
4 answers
1k views

Could dark energy be the effect of gravity at great distances?

This may be a silly question, but is it possible that dark energy and gravity are related to each other? Space-time is deformed everywhere in space by objects with mass. The more massive the object, ...
user avatar
5 votes
2 answers
955 views

Is cold dark matter made of Higgs bosons?

This paper (2010) hypothesizes that Higgs bosons might be absolutely stable, allowing them to serve as a cold dark matter candidate: The Higgs boson is in the backbone of the standard model of ...
user44629's user avatar
  • 301
5 votes
3 answers
4k views

Relation of General Relativity to Dark Matter and Dark Energy

I was reading an elementary book on dark matter (in fact, a historical perspective) and there were mentioned how the scientific community react to the idea of dark matter proposed as a solution to ...
Arbër Ll's user avatar
3 votes
1 answer
483 views

Dark matter, dark energy [closed]

As I understand dark matter and dark energy are quite theoretical . That modern theories require the existence of these phenomena. I read a lot of information about this. And I realized that ...
Karina's user avatar
  • 31
2 votes
1 answer
520 views

Where are particles dissappearing in thermal equilibrium?

I am incredibly puzzled over dark matter relic abundance plots like this (taken randomly from google), where it shows number density of some particle species in a comoving volume In thermal ...
Wint's user avatar
  • 71