Questions tagged [dark-matter]
Matter not observed directly but inferred to exist based upon its gravitational effects.
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Gravity as a repulsive force
As we know that universe is expanding, why can't we think the gravitational force as repulsive in nature in the realms of dark matter and dark energy?
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Primordial dark matter synthesis
In standard cosmology, there is a general picture of:
Primordial nucleosynthesis, i.e., when and how, nuclei or elements were formed. It is not quite tested, but it is more or less known where it ...
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Rulers, Chronometers and Scales [on hold]
Some child questions still makes me wonder why or where is the limit between the classical and regular world, even Einstein's Special and General Relativity, from quantum world, both of them share the ...
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2answers
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How do you distinguish between missing momentum from a neutrino and from dark matter?
I thought googling this would give me an answer quite quickly, but actually couldn't find much, so maybe it's a silly question. But I read that dark matter searches rely on measuring missing momentum ...
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What is the mass/cross section of Dark Matter candidates?
I understand that experiments at LUX, XENON and LHC have eliminated many of the predicted masses for candidates for Dark Matter. Does anyone know what the current lowest possible mass is that hasn't ...
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1answer
120 views
Core of Earth exists as dark matter [closed]
I have read recent scientific speculation that the core of the Earth,i.e. Dark matter "hair" flowing through the earth and https://www.thoughtco.com/dark-matter-role-in-galaxies-3072059 ...
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41 views
What proof do we have that dark matter is matter? [duplicate]
The Dark matter page on CERN's official website describes dark matter as if it were regular matter just with some mysterious properties. This was a surprise to me because every time someone mentions ...
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25 views
Generally how much faster are stars on the outskirts of galaxies orbiting than they should be?
This assumes there is no mysterious matter causing the extra speed. Are they orbiting say 10% faster than expected etc?
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54 views
Dark Matter Stars Triggering Nebula Collapse
I'm interested in theories of dark matter where dark matter is an equivalent copy (or copies) of ordinary matter. Each equivalent sector is hidden from the others would see the others as 'dark' and ...
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1answer
157 views
Formula for the bias of galaxies
From the article "Large-Scale Galaxy Bias", I try to deduce the equation that my teacher told me which links 2 quantities:
the global number density of galaxies
the local number density of galaxies
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2answers
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Dark matters, what it is made of? [closed]
Where does DARK MATTER come from? How it is made? Can someone make it artificially? Can it be altered also like normal matter? Or what is it different from matter and anti-matter, and what is it made ...
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Demonstration about large-scale bias of galaxies
From this article : https://arxiv.org/pdf/1611.09787.pdf , I try to deduce the equation that my teacher told me which links 3 quantities :
1) the global number density of galaxies
2) the local ...
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0answers
11 views
How does the cosmological constant dominate cold matter perturbations?
I have been studying inhomogeneous universe in physical cosmology, whereupon I arrive at cold matter perturbations which are dominated by various background fluids. I understood the solutions for the ...
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Spiral galaxy stability
Is there a limit of baryonic masses $M_{B}$ ($M_{B}=M_{\star}+M_{g}$), beyond which a spiral galaxy is no longer rotationally supported? Like for example: Could spiral galaxies of baryonic masses $M_{...
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2answers
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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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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
102 views
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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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
50 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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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
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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
59 views
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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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
57 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
118 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
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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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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
105 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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2answers
41 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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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
96 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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60 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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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
35 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
58 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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1answer
56 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
102 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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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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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 ...
