Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [dark-matter]

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

0
votes
1answer
41 views

How do we know the quantity of dark matter in the universe?

I have been reading on dark matter and it is given specific numbers of its quantity, i.e, ~27%, in the universe. How we come up with that number as we have no strong opinion what it is made of? We ...
3
votes
0answers
27 views

Integral of Bolzmann distribution function for dark matter (modern cosmology)

In Dodelson's textbook modern cosmology ch4.5, I wonder if anyone knows how he did the integration by part over the phasespace on the distribution function of Eq(4.72) and Eq(4.78). Here is part of ...
-3
votes
1answer
60 views

Dark energy and dark matter difference

From the rotation curve of spiral galaxy it is found that for (>>r ) the total mass is not concentrated at the centre but varies as ~r for which the rotational velocities of the stars far from the ...
0
votes
1answer
91 views

Effects of dark matter

I was wondering, when sims of galaxies show that we need dark matter to account for the movement of outer stars, are models taking into account relativistic effects on gravity? The tips of spiral ...
0
votes
0answers
30 views

Does dark matter experience drag?

Is dark matter dragged around the galaxy by gravity as stars and groups of stars orbit the galaxy, and, if so, is its shape/distribution deformed? Similarly, would the Oort cloud be deformed by being ...
2
votes
3answers
89 views

Mass of potential gravity energy?

Assume a system where there only two 1 kg solid iron balls floating in space. The two balls are touching each other, so the potential gravitational energy between them is 0. Now I move them 1000 m ...
1
vote
2answers
81 views

Doesn't dark matter imply a new force?

Given that every particle that we have experimental confirmation of is an oscillation of its field (from what we know), and given dark matter is thought to be a particle yet undiscovered according to ...
0
votes
1answer
33 views

Dark Matter gamma-ray flux from hadronic annihilation channels?

For a project I am currently reading into indirect detection of Dark Matter via gamma-rays from DM subhalo's. I understand that there is a possibility of DM annihilating with each other in these ...
-2
votes
2answers
127 views

Could photons decay into Dark Matter? [closed]

So, we can "see" 13.7 billion (intentionally not including expansion) light years in all directions and we "see" a red shift. What if, the reason we can't observe photons beyond this limit is that ...
1
vote
1answer
79 views

Why is the heat death, rather than a Big Crunch, the most accepted theory of the ultimate fate of the Universe?

The Heat Death is accepted by most as the end of the Universe, but how can that be? Wouldn't the Big Crunch make a lot more sense? I mean, even if everything in the Universe is spread out uniformly ...
19
votes
5answers
4k views

If perfect blackness violates the Uncertainty Principle, how isn't dark matter a violation?

In a recent tweet, Dr. Michio Kaku stated that perfect blackness would violate the Heisenberg Uncertainty Principle, i.e. every object must emit some radiation. I have two questions regarding this ...
2
votes
1answer
121 views

Why are we trying to fit GR in QFT when there's a chance that GR is incomplete?

GR explains most phenomena in our universe, but not everything.. Dark matter and Dark energy still don't fit in explanation of GR. QFT, on other hand, is almost complete. Shouldn't physicists go for ...
-1
votes
2answers
43 views

How much light is needed to quality as possible dark matter candidate?

I know when scientists study dark matter they have already excluded light because of it's negligible effect on the galaxy and of course we are able to observe it directly, I am curious just how much ...
1
vote
2answers
133 views

Farnes, cosmology involving negative mass

I came across a paper recently which seems to be getting a lot of popular press, and a student also emailed me to ask about it: -- Farnes, "A Unifying Theory of Dark Energy and Dark Matter: Negative ...
4
votes
2answers
141 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 ...
6
votes
1answer
610 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 ...
2
votes
1answer
69 views

Can we weight dark matter?

We can observe the effect of light as it gets bended in the presence of dark matter, and I wonder how is it possible to measure their mass given that we can't see them and they don't interact with ...
2
votes
1answer
55 views

Dark matter relative velocity

In Dark Matter Indirect Detection literature, it is usually said that the relative velocity of dark matter particles in the galactic halo is about $$ v \sim 10^{-3}c$$ See for an example this lecture ...
2
votes
1answer
23 views

How can I understand the reaction rate of WIMP dark matter intuitively?

I'm reading a cosmology textbook(sorry it's Japanese) and stacked at statement that If the mass of WIMP is enough smaller than 100GeV, the reaction rate is represented as $\langle \sigma_a |\mathbf{\...
-1
votes
1answer
72 views

Chemical equilibrium for a $2-2$ scattering and Boltzmann equation in cosmology and astroparticle physics

Definition of chemical equilibrium According to the definition of chemical equilibrium in Wikipedia, it is a situation where the rate of the forward reaction is same as the rate of backward reaction ...
2
votes
2answers
106 views

Dark matter density calculation

I find that the general dark matter density of the Milky Way is $$6.87 \times 10^9 \: \rm GeV/m^3$$ or $$1.225 \times 10^{-17} \: \rm kg/m^3$$ (by taking the size of the Milky Way and dividing it to ...
2
votes
1answer
117 views

Light neutrino number from the invisible decay width of $Z$ boson, and precluding heavy neutrinos as dark matter candidate

The $Z$ boson decays into pairs of quarks and leptons. While the decays to quarks pairs and charged lepton pairs can be observed, the decays to $\nu\bar\nu$ are cannot be. By subtracting the visible ...
4
votes
1answer
50 views

Speed of solar system through dark matter halo

How is the speed of the solar system through the dark matter halo determined? Direct dark matter detection experiments rely on this speed estimate. Assuming the sun/earth travel through the dark ...
1
vote
1answer
54 views

Do attraction between two galaxies count for dark matter?

We know that the uniform rotation curve of individual spiral galaxies does require presence of some form of dark entity (matter). Does the attraction between two (or more) spiral galaxies also require ...
7
votes
4answers
3k views

Could dark matter consist of the supermassive black holes at the centers of galaxies?

Inspired by this question about whether dark matter is matter, noting that dark matter tends to be clumped in galaxies near the center and less so on the edges, accepting that many (most?) galaxies ...
18
votes
3answers
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 ...
1
vote
1answer
89 views

Is the dark matter present only around the galaxies?

Dark matter is believed to give galaxies its shape and prevent them from flying apart. Is dark matter present only on outer edges of the galaxy or is it present throughout the galaxy?
1
vote
1answer
68 views

Like the Higgs sector of the standard model, is there a SUSY sector which is also such a sector?

This question arose from an application of the virial theorem that showed how Bose-Einstein condensates of astrophysical dimension could arise from condensing clouds of normal phase bosons. If these ...
1
vote
1answer
35 views

Are sterile particles actually part of the strong interaction?

Suppose that instead of doublets consisting of lepton/neutrino flavor eigenstates, the sterile neutrino is a pure singlet with zero flavor. Then, since there would be no partner lepton for it to ...
1
vote
0answers
17 views

Population histograms and relationship between size of galactic disk and amount of dark matter

I am interested in seeing a plot of dark to baryonic matter ratios in terms of the galactic disk size (when it applies, as not all galaxies fit into disk shapes, and probably analyzing disk galaxies ...
1
vote
0answers
47 views

Elementary particles and halo of matter - rookie question [duplicate]

I'm super new to this Stack and even newer to physics. To be honest, I am currently reading an introductory book on physics called "Seven brief lessons of physics" by Carlo Rovelli (the very first ...
3
votes
1answer
52 views

What formula is used to make exclusion plot in the direct detection of dark matter?

The idea of direct detection of dark matter is that a dark matter particle striking some underground target will cause the target nucleus to recoil. From the recoil, one can determine the scattering ...
1
vote
1answer
151 views

Why does dark-matter distribute in spherical shape around the galaxy?

For visible matter, due to spin dominance over gravity while formation of galaxy, planar symmetry of a galaxy is achieved and the galaxy will be planar (spiral). But dark matter's distribution is ...
1
vote
0answers
41 views

Star orbit and dark matter [closed]

In a college entrance examination of my country, there was the following question: Suppose that, in a galaxy, the dark matter, which is evenly distributed, can be removed. Suppose also that in the ...
0
votes
1answer
226 views

Is dark matter a superfluid?

The fact that the dark matter halos surrounding colliding galactic clusters simply pass through each other without interacting has a simple explanation. If they are superfluid bodies, wouldn't be ...
0
votes
1answer
49 views

Could space repel mass?

I'm not an advanced physics person, so any explanations need to be reasonably low-level... I was looking at oil/water bubbles (hydrophobic vs hydrophylic molecules) and it got me thinking about the ...
0
votes
1answer
70 views

Can/do Virtual Particles have mass/energy?

Apologies, as you can tell I am not an expert... My question arose during a thought experiment regarding that elusive Dark Matter/Energy and the rate at which the universe should be expanding. It ...
2
votes
1answer
87 views

How is it possible to produce a Bose-Einstein condensate of astrophysical dimension?

There is simple mechanism behind such a production and it suggests that a cloud made of bosons could collapse gravitationally into an equilibrium polytrope in the condensate phase. Assuming that ...
2
votes
1answer
84 views

Is it possible to break supersymmetry in such way that the SUSY partners of the known particles have a much lower mass as opposed to greater?

To continue, is it possible to break SUSY in a way that leaves some of the SUSY partners about equal in mass? These issues arose in connection with an unpublished ab initio calculation of the ...
1
vote
2answers
81 views

Does dark-matter attract itself with gravity as light-matter does, and if so where are the dark stars and galaxies?

Does dark-matter interact with gravity like light-matter does, or does dark matter interact only with light-matter via gravity?
2
votes
0answers
80 views

Could alternate charges exist? [duplicate]

Currently there is 1 known type of electric field, it has positive(positrons and protons) and negative(electrons) charges. I would expect the charges of alternate electric fields to act the same ...
3
votes
1answer
125 views

Galaxy Rotation Speeds and General Relativity

Is it true that the predictions from the General Theory of Relativity don’t match the observations of galaxy rotation speeds, and that this then started the search for dark matter? Is it only the ...
-1
votes
1answer
63 views

Dark matter or Misunderstanding: Is it possible that the dark matter is simply missed variables in the math?

Is it possible that the dark matter is simply missed variables in the math? I am not a physicist but examples might include: effects of planetary and galaxy rotation, electromagnetic fields, ...
0
votes
1answer
93 views

What kind of modified gravity could still explain all dark matter claims if we never more directly detect dark matter? [closed]

I'm curious about this. I saw this: https://www.forbes.com/sites/brucedorminey/2018/07/18/is-time-running-out-on-dark-matter/ and they're suggesting that as direct searches for dark matter more and ...
0
votes
1answer
98 views

Dark matter pressure

Dark matter is suppose to form large halos of unknown yet type of particle with a specific density density profile. Does the dark matter halo can be viewed as a fluid of particles with density and non-...
17
votes
2answers
4k views

How long has dark matter been around?

I've read that dark matter's existence is theorized because galaxies spin/clump in a way that would require much more mass than there appears to be. Also that there is gravitational lensing in places ...
45
votes
2answers
5k views

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 ...
1
vote
1answer
88 views

Could mass also experience a form of gravitational redshift?

Main question Gravitational redshift for photons are a wellknown phenomena where the electromagnetic radiation is reduced in frequency and thus the wavelenght is increased. The wave–particle ...
3
votes
1answer
67 views

What is the effect(s) of the kinetic decoupling of WIMPs after it has frozen out?

After freeze-out, the WIMPs departed from chemical equilibrium and till today, it maintains a constant number density. That appears enough to account for the observed relic density. But we also assume ...
1
vote
1answer
239 views

Why are there a bunch of cosmological coincidences?

There are several cosmological parameters that are more or less of the same order $10^{-60}$ (in Planck unit), namely, inverse of the age of the universe $$ \frac{1}{t_0}, $$ Hubble constant $$ H_0, $...