Questions tagged [dark-matter]
Matter not observed directly but inferred to exist based upon its gravitational effects.
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Why is the distribution of dark matter in a Galaxy different from the distribution of normal matter?
The dynamics of a galaxy are driven by gravity. And dark matter experiences the same gravitational forces as normal matter. The effects of other forces are very small in comparison. So why is the ...
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Could apparent horizons of accelerated particles explain dark matter? [closed]
There are some interesting discussions at stackexchange about apparent horizons of accelerated particles (accelerated matter). Relevant links can also be found here SE question 1, SE question 2 SE ...
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Dark matter composition [closed]
I assume that dark matter is made of heavy neutrinos.But wouldnt they be converted into neutrinos with less mass throygh weak interaction?So dark matter isnt made of neutrinos.I think there is truly ...
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1answer
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Dark Matter Wave Particle Duality
CERN is looking for dark photons, and they are seeking to look for interactions with the Higgs boson with the dark photon.See link here. So in other words a dark photon - a mediator for dark matter is ...
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0answers
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How well supported by observations is the hypothesis that concentrations of dark matter are essential to galaxy formation?
Much work regarding the formation and early evolution of galaxies seems to assume that galaxies form based on clumps dark matter.
The following observations indicate that some galaxies started with ...
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2answers
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Why physical / cosmological models that have been falsified weren't abandoned? [closed]
Before anything, I'd like to say that I'm a layman (non physicist) and english is not my main language; I apologize if my choice of words make me sound rude / arrogant, that is not my intent.
I often ...
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1answer
48 views
Dark matter and supersymmetric particles
Is there a possibility to consider supersymmetric particles of fermions and bosons as the unknown dark matter?
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0answers
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Dark Matter search, why DAMA collaboration does not publish $S_0$?
Results from recent experiments are starting to come in, mostly in the direction of not confirming the annual modulation measuremements published by the DAMA/Libra collaboration. In the search for ...
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1answer
54 views
How do they know the numbers of the energy pie chart of the universe?
They say that the total energy of the universe consists of 4.9\% ordinary matter, 26.8\% dark matter and 68.3\% dark energy. I hear this pie part in virtually every lecture in cosmology. How do we ...
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How do we know that dark matter energy density scales as $\rho\propto a^{-3}$?
How do we know that dark matter energy density scales as $\rho\propto a^{-3}$?
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1answer
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Why use xenon in the search for dark matter?
The XENON dark matter research project is an interesting long-running project that strives to detect dark matter. I understand that the basic principle of the project design is that WIMPs are expected ...
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0answers
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Axion CDM analogous to reheating?
In a paper on Axions Peccei writes:
When the Universe goes through the PQ phase transition at $T ∼ f_a >
> Λ_{QCD}$ the QCD anomaly is ineffective. As a result, early in the
Universe $< ...
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1answer
55 views
Explanation for Dark Matter [closed]
My question relates to dark matter (DM). I understand that primordial black holes have been ruled out statistically as a candidate for DM. Could “dead” primordial black holes leave behind curved ...
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1answer
115 views
Is a galaxy made up of dark matter really a galaxy?
So I am watching a video discuss Dragonfly 44. The galaxy is made up almost entirely of dark matter and is 100x dimmer than the Milky Way galaxy.
Wouldn't this mean it is just a large clump of ...
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1answer
63 views
Could six copies of the universe exist only interacting by gravity? [closed]
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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1answer
46 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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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
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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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2answers
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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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1answer
118 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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1answer
85 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
57 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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3answers
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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
34 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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0answers
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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
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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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1answer
55 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
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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
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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
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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
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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
38 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
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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
145 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
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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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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
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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
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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
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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
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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
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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 ...
