Questions tagged [dark-matter]

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

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5
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2answers
174 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 ...
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1answer
643 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 ...
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1answer
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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 ...
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1answer
65 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 ...
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1answer
25 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{\...
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1answer
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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 ...
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2answers
226 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 ...
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1answer
172 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 ...
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1answer
64 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 ...
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1answer
68 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 ...
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4answers
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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 ...
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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 ...
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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?
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1answer
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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 ...
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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 ...
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0answers
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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 ...
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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 ...
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1answer
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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 ...
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1answer
187 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 ...
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0answers
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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 ...
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1answer
249 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 ...
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1answer
52 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 ...
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1answer
86 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 ...
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1answer
90 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 ...
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1answer
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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 ...
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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?
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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 ...
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1answer
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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 ...
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1answer
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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, ...
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1answer
110 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 ...
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1answer
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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-...
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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 ...
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2answers
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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 ...
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1answer
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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 ...
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1answer
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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 ...
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1answer
247 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, $...
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1answer
282 views

Why is the dark matter freeze-out temperature $T\sim \frac{m}{20}$ so generic?

For a dark matter of mass $m$, the typical freeze-out temperature is $T$ is usually assumed to be between $\frac{m}{20}-\frac{m}{25}$. But the freeze-out temperature depends upon the annihilation ...
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1answer
54 views

Is it sufficient to consider the uncharged dark matter and a $\mathbb{Z}_2$ symmetry to prevent its decay into photons?

Higgs boson, though electrically neutral, can decay to produce a pair of photons i.e., have electromagnetic interactions. See the answer here. Therefore, it appears that making dark matter ...
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0answers
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What might be the equillibrium Distribution Function of Dark Matter?

Can we assign a thermal distribution function to Dark Matter(not necessarily known ones)? Is it possible that they won't even follow thermal distribution function and maybe a function of something ...
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2answers
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Could a black hole's dark matter content be determined?

I recently attended a talk where the speaker said that it is impossible for us gain information about the history of particles which make up the black hole. i.e we won't know if the black hole was ...
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Experimental constraints on dark matter pressure?

The $\Lambda$CDM model assumes collisionless dark matter, so that its pressure $P=0$. But what are the best experimental constraints on $P$? I guess on $P/\rho$ in fact…
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1answer
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Why can't the Higgs vacuum energy clump to galaxies and act as dark matter (instead of dark energy)? [closed]

The Higgs field has a nonzero vacuum expectation value which contributes to the energy density of the Universe. Energies contribute to the curvature of spacetime and affected by gravitational ...
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2answers
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Dark Matter and Gravity

If gravitational lensing implies that Dark Matter exerts gravity onto light then why are the stars and regular matter not clustering around Dark Matter?
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1answer
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Why are cosmological contents often modeled as fluids?

Why is it that in cosmology, everything is treated as a "fluid"? What justifies modelling radiation, matter, etc. as "fluids" (even dark energy??)? When does it break down -- surely at small scales ...
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1answer
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Exclusion limits on particle dark matter

I'm trying to make sense of how the upper limits of the cross-section of particle dark matter (WIMPs) are computed, like in the figure below. This is taken from an article on dark matter searches. ...
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What gives mass to dark matter particles?

Assuming that dark matter is not made of WIMPs (weakly interacting massive particles), but interacts only gravitationally, what would be the possible mechanism giving mass to dark matter particles? If ...
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2answers
206 views

Is there any evidence for dark matter besides gravitational effects?

Is there any evidence for dark matter besides just its gravitational effects? What I’m getting at is...why are we so quick to assume it’s any kind of “matter” at all rather than just some unexplained ...
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1answer
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Article presenting first evidence for dark matter?

What are the papers where the first evidence for dark matter related with the stability of galactic discs, and the orbits of galaxy satellites?
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Is dark matter unmanifested matter? [closed]

I am by no means a physicist. I lack credentials and formal education. I did however have an interest in theoretical physics when I was younger. This post is to present my thoughts/idea/theory or ...
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How do we know that the dark matter is cold or non-relativistic? [duplicate]

According to the $\Lambda$CDM parametrization of the Standard Model of Big Bang cosmology, the universe contains a cosmological constant $\Lambda$ associated with $73\%$ dark energy, $23\%$cold dark ...