Questions tagged [dark-matter]
Matter not observed directly but inferred to exist based upon its gravitational effects.
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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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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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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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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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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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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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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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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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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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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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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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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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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
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 ...
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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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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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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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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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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
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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,
$...
