Questions tagged [dark-matter]

Matter not observed directly but inferred to exist based upon its gravitational effects.

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46
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8answers
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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 ...
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3answers
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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 ...
46
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4answers
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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?
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4answers
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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 ...
36
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1answer
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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 ...
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5answers
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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, ...
31
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5answers
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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 ...
6
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4answers
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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 ...
3
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2answers
343 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 ...
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2answers
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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 ...
21
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5answers
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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 ...
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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 ...
11
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2answers
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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 ...
7
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2answers
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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?
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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?
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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?
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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....
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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 ...
8
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1answer
468 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?
3
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2answers
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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 ...
18
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1answer
590 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 ...
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2answers
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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 ...
23
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2answers
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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 ...
19
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2answers
652 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 ...
7
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2answers
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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 ...
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3answers
655 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 ...
5
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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?
19
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3answers
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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. ...
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4answers
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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 ...
14
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2answers
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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 ...
13
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6answers
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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 ...
12
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1answer
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How the CMB anisotropy is linked to the existence of cold dark matter and dark energy?

After the data from the cosmic microwave background has been collected by WMAP or Planck, what types of analysis is needed to conduct in order to deduce the cold dark matter density and the ...
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2answers
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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 ...
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1answer
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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 ...
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6answers
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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 ...
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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 ...
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3answers
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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 ...
5
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2answers
838 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 ...
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2answers
555 views

Why is dark matter the best theory available to explain missing mass problems?

Why is dark matter the best theory to explain the missing mass problem? Why is dark matter mathematically necessary to explain the missing mass problem? On a side not I believe dark matter is ...
31
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3answers
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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. ...
6
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2answers
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How bad would it break physics if dark matter was not “particles”?

Some people suggest that dark matter might not even be particles at all —that’s just what physisists expect to find with reference to what they are familiar with. But, I learned, from layman books of ...
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1answer
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Is matter - dark matter symmetry possible?

The gravitational lensing evidence suggests massive and relatively dense accumulations of dark matter in space. However, dark matter collapsing to dense regions is unlikely due to energy conservation. ...
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2answers
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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 ...
18
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3answers
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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 ...
8
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1answer
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What is a flat rotation curve?

Was reading about dark matter and the distribution of it throughout the galaxy. it said "For example, if rotation curves are flat this means-" what exactly does this mean?
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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 ...
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4answers
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Can the Sun / Earth have a dark matter core?

If dark matter interacts with ordinary matter at all, it should most likely occur where ordinary matter is densest. Hence we have papers about neutron stars possibly containing dark matter cores (...
9
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5answers
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What makes the stars that are farther from the nucleus of the galaxy go faster than those in the middle?

It has no sense that stars that have a bigger radius and apparently less angular speed($\omega$) goes faster than the ones near the center.
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3answers
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What exactly is 'Dark Matter'? [duplicate]

There are many documentaries, forums, blogs and more dedicated to Dark Matter. I have been frantically searching for an answer to my question however none of my sources have clarity to the matter of ...
6
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1answer
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Experimental Data for Mass Distribution of a Galaxy

My goal here is not to discuss dark matter in general. I know there are many other observational clues that hint us towards Dark matter. My goal is simply to understand this argument here a little ...