Questions tagged [dark-matter]
Matter not observed directly but inferred to exist based upon its gravitational effects.
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Could six copies of the universe exist only interacting by gravity? [on hold]
The ratio of dark matter to matter is roughly in proportions $1:5.4$
This suggests that if there were about 6 Universes placed in the same space that were completely invisible to each other, except ...
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2answers
37 views
Are pressureless, collisionless and self-interacting dark matter all synonymous?
Is there any distinction between pressureless, collisionless and self-interacting dark matter or does being one imply the other?
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No dark matter, weight of the universe measured by luminosity is unaccounted/distorted relections? [closed]
If calculating the universe's mass by luminosity, how do we account for all the combined reflections from our planets or planets from other solar systems, and throughout all of time and space? And can ...
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2answers
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Do we need dark matter and dark energy, if the behaviour of the universe in its initial stages was similar to that of the Sun? [closed]
According to CMBR the universe was a cloud of plasma and was a perfect black body, $380,\!000$ years after big bang.
But the Sun in our solar system also is in the state of plasma, thus making it a ...
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1answer
72 views
Neutron decay discrepancy
I have been reading the article Neutron Lifetime Puzzle Deepens, but No Dark Matter Seen on the present methods of measuring the life span of neutrons The bottle method measures a mean lifespan which ...
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36 views
What is the current status of interpretation of $130$ GeV photons from the galactic center?
The observed spectrum of photons coming from the galactic center has a sharp line at $130$ GeV which for some time was thought to be a signature of WIMP annihilation. But the bounds on WIMP cross-...
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2answers
31 views
Does Higgs Boson influences with Gravity?
Does Higgs Boson influences with Gravity? Is there any way that if the universe is expanding Higgs particle has influence over it?
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114 views
Why does not dark matter gather and form celestial bodies? [duplicate]
since the only thing we know about dark matter that it "attracts" and affect our Baryonic matter's momentum and speed, which means that it does have mass of a sort.
so why didn't we witness a ...
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65 views
black dwarf stars and dark matter
Today we understand that a black dwarf star represents a hypothetical star that is the result of the complete consumption of the energy of a white dwarf which is the remnant of a star of little or ...
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1answer
51 views
Which decoupled first? The dark matter or the CMB photons?
According theories that work best for the structure formation which happened first in the history of the evolution of the Universe, the decoupling of dark matter or the decoupling of photons? How sure ...
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1answer
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Does string/M-theory provide a solution to the dark matter/energy problem?
Would string theory or any other propesed UFT help explain, at least in theory what the other 95 percent of matter and energy in the universe are about?
It seems as thaugh there is a reacurring theme ...
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1answer
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Why doesn't the centrifugal force cause rotating dark halos to flatten?
Consider a spherical cloud of dark matter like the spherical halo around our galaxy. Please see the diagram below
Assuming that the halo is purely made up of dark matter which has only gravitational ...
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1answer
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Dark matter should be nonrelativistic at $1$ KeV or earlier. Why?
If the dark matter (DM) is non-relativistic at freeze-out and if the kinetic decoupling occurs much later than freeze-out, it is called cold dark matter. More precisely, it is stated that if the DM ...
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4answers
75 views
Can we measure dark matter's effect on spacetime?
I'm not a physicist or mathematician at all, just very curious, so sorry if this is a dumb question.
Now I understand we can make astronomical observations and say, "Oh, 85% of gravity in the ...
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1answer
30 views
Does dark matter need a second force to collect in ordinary matter?
Some experiments search for dark matter interactions at the center of bodies like the Sun and Earth, assuming that if there is some interaction with ordinary matter that allows dark matter to lose ...
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A doubt in Modified gravity
I am new to dark matter and modified gravity so excuse and inform me if I am wrong.
If changes are made in the Friedman equations then there wouldn't always be an underlying action action principle. ...
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1answer
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Could dark matter be normal matter that is beyond the observational horizon?
As I understand it, matter that is too distant for its light to reach us would not be observable, and the CMB is the limit of what is observable from our location within the universe. Could what is ...
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1answer
54 views
Might a “normal matter” body orbit a dark matter body?
Are there any main stream theories of dark matter that would allow for it to form bodies which could participate in orbits with normal matter?
So, say, could a normal matter planet be captured and ...
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51 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 ...
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1answer
55 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 ...
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1answer
71 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 ...
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1answer
96 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 ...
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0answers
32 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 ...
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3answers
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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 ...
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2answers
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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 ...
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1answer
36 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 ...
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2answers
150 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 ...
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1answer
108 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 ...
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5answers
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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 ...
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1answer
145 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 ...
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2answers
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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 ...
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2answers
163 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 ...
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2answers
153 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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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
72 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 ...
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1answer
59 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
24 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
77 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 ...
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2answers
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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
143 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
59 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
58 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
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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
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 ...
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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 ...
