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

learn more… | top users | synonyms

48
votes
1answer
1k views

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 ...
32
votes
2answers
1k views

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 ...
30
votes
4answers
4k 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?
29
votes
3answers
3k views

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 ...
22
votes
4answers
2k views

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 ...
21
votes
6answers
2k views

Why isn't dark matter just matter?

There's more gravitational force in our galaxy (and others) than can be explained by counting stars. So why not lots of dark planetery systems (ie without stars) ? Why must we assume some undiscovered ...
20
votes
1answer
953 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 ...
20
votes
3answers
2k 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 ...
19
votes
2answers
1k 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 ...
18
votes
2answers
3k 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 ...
17
votes
2answers
916 views

Correlation between outstanding hints in experimental particle physics

The 115 GeV ATLAS Higgs with enhanced diphoton decays has gone away but there are several other recent tantalizing hints relevant for particle physics, namely CoGeNT's 7-8 GeV dark matter particle ...
14
votes
5answers
552 views

How does dark matter collapse?: Entropy considerations

Inspired by this question. I believe that the usual explanation that preserves the second law of thermodynamics as an astrophysical gas cloud collapses under gravity is that the gas must heat and ...
14
votes
2answers
400 views

Does it make sense to continue searching for dark matter on Earth?

The Large Underground Xenon Detector (LUX) recently released results1 that they have found no signs of dark matter2 after a ~3 month search this spring and summer. The LUX group plans to spend all of ...
13
votes
2answers
772 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 ...
13
votes
2answers
383 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 ...
13
votes
1answer
405 views

Dark matter and SO(10) grand unification

$SO(10)$ grand unified theories nicely accommodate a massive $\sim 10^{14-15}\; GeV$ sterile neutrino. Would this be a viable dark matter candidate? I haven't found any specific material regarding ...
12
votes
3answers
2k views

Why don't stars have Keplerian orbits?

In a comment to Rob Jeffries' answer to this question on spherical galaxies, Incnis Mrsi commented There should exist the entire range of orbits in a spherically symmetric system: near-circular, ...
12
votes
2answers
2k views

Is dark matter repulsive to dark matter? Why?

I think I saw in a video that if dark matter wasn't repulsive to dark matter, it would have formed dense massive objects or even black holes which we should have detected. So, could dark matter be ...
12
votes
1answer
312 views

Distribution of Dark Matter around galaxies

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 ...
11
votes
5answers
3k 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 ...
11
votes
1answer
534 views

Justification for new theories of Particle Physics and General Relativity

In reference to arxiv:1212.4893v3 and arxiv:1206.5078v2 papers of Ma and Wang, they have proposed new theories in particle physics, the weakton model where quarks and leptons are formed using these ...
10
votes
1answer
955 views

Why do we need to find 5 Higgs Bosons to prove the existence of the dark matter?

I was recently watching a show that say we need at least 5 Higgs Boson to prove the existence of the dark matter because it will strengthen the concept of symmetry. Why is that so? Because, I am not ...
10
votes
6answers
2k views

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 ...
10
votes
2answers
1k views

Do we have an idea about the amount of matter in the universe?

Do we consider the amount of matter in the universe to be "infinite"? Or do we have an idea about "how much" there is?
10
votes
4answers
990 views

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 ...
10
votes
2answers
405 views

Does the Milky Way have dark matter satellite galaxies?

This recent paper by Weinberg et al. discusses that one potential problem with our current model of Cold Dark Matter (CDM) is that is predicts a greater number of satellite galaxies for the Milky Way ...
9
votes
5answers
1k views

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 ...
9
votes
2answers
575 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 ...
9
votes
2answers
718 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 ...
9
votes
1answer
293 views

What dark matter can AMS currently find (or exclude)?

The rumor mill is running again, this time it's about the AMS experiment (Alpha Magnetic Spectrometer) that's going to make a major announcement soon. I suppose they are looking for peaks in gamma ...
9
votes
1answer
235 views

Can curvature waves in f(R) theories explain gravitational lensing in cluster collisions?

The Einstein-Hilbert action leading to Einstein's equations is $$S\sim\int R \sqrt{-g}\, {\rm d}^4 x$$ There is a class of modifications of Einstein's relativity called $f(R)$ theories of gravity ...
9
votes
2answers
84 views

CMB curly B-modes and dark matter

I raised a question a while ago regarding weak gravitational lensing of galaxies and the CMB. With all the fuzz with the BICEP2 data, I think it is time to raise even more questions about this amazing ...
8
votes
3answers
137 views

What's dark matter and who discovered it?

I have heard about dark matter that's called the Master Of The Universe. What's this and is the dark matter the reason galaxies exist?
8
votes
2answers
1k views

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 ...
8
votes
5answers
548 views

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.
8
votes
5answers
455 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 ...
8
votes
1answer
368 views

What properties of Germanium make it suitable for Dark Matter detectors?

What properties of Germanium make it suitable for Dark Matter detectors? I tried googling but there was too many results describing the use of Germanium Chrystals at low tempretures for Dark Matter ...
8
votes
3answers
495 views

What current alternatives are there to the standard concordance model of cosmology?

The current "standard model" or concordance model of cosmology is Lambda CDM which includes late time acceleration due to a cosmological constant, cold dark matter as the missing matter component and ...
8
votes
1answer
395 views

Does dark matter have to be matter?

There is a very similar question to this one: Is dark matter really matter?. But the particular aspect I'm asking about seems not to be mentioned there. So, here we go: Does dark matter have to exist ...
8
votes
0answers
270 views

Dark matter clumping [duplicate]

How can dark matter particles (WIMP's) get ever more densely clumped during the evolution of the universe, as we see for example in the Millennium simulation, if they can't loose kinetic energy by ...
7
votes
2answers
369 views

Did CDMS identify dark matter?

A recent paper by the CDMS collaboration (PRL here and free text here) makes this statement in the abstract: This blind analysis of 140.2 kg day of data taken between July 2007 and September 2008 ...
7
votes
2answers
375 views

Why does dark matter form walls and filaments

Related: How are galaxy filaments formed? And do they have any analogues in stellar formation? But I want to come at this from a different angle. Like the user asking that other question, I was a bit ...
7
votes
1answer
41 views

Temperature of WIMPs

As a dark matter candidate, what should be the temperature and kinetic energy (or also the speed) of the WIMPs (weakly interacting massive particles) to agree with the observed distribution of dark ...
7
votes
1answer
170 views

Could the dark matter sector be boring?

People always talk about finding good dark matter (DM) candidates of beyond Standard Model (SM) theories. To be a proper candidate the particles should not decay into the SM particles and could ...
7
votes
2answers
271 views

Would dark matter absorb gravitational waves?

Would the vast and seemingly diffuse clouds of dark matter floating around our galaxy (and most others) absorb gravitational waves? Is this perhaps why we haven't detected any yet?
6
votes
2answers
517 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 ...
6
votes
1answer
286 views

Could dark matter be a kind of Goldstone boson?

The common argument for vanishing Goldstone boson is like, if there is some massless particle generated from the spontaneous symmetry breaking, it should be detected. Since we never saw that, it is ...
6
votes
4answers
591 views

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 ...
6
votes
2answers
401 views

How convincing is the evidence for dark matter annihilation at 130 GeV in the galactic center from the Fermi Satellite data?

I listened to Christoph Weniger present his results at SLAC today. See his paper is here: http://arxiv.org/abs/1204.2797 and also see a different analysis here: http://arxiv.org/abs/1205.1045. The ...
6
votes
3answers
517 views

If the universe is full of dark matter, why is it only 2.73 K cold?

people! I am just a physics layman, but I recently watched a documentary about the universe and it was told that the universe is full of dark matter and energy and the universe is empty, so that ...