All Questions
Tagged with cosmology dark-matter
265
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Gravitational halos made of neutrinos...?
I have been recently interested in how halos made of standard model particles could be formed and behave.
After asking some questions in this site, I was told about how neutrinos could form such halos....
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1
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70
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If dark matter is axion particles, how did such light particles slow down?
One candidate for dark matter is axions and there is tentative experimental evidence for their existence.
Axions are very light, most models weigh them in at tiny fractions of an eV. It seems like ...
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2
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1
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253
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What's the meaning of 'cold' in the CDM model?
On Wikipedia, it says
In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% ...
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2
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Test of the primordial black hole solution to dark matter
One of the ideas that might solve some of the dark matter problem are the existence of many small black holes. There is evidence, in principle, for the existence of these small black holes via the ...
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Why do people say that the $\Lambda$-CDM model has six independent parameters?
The Wikipedia article on the $\Lambda$-CDM model says that the model has six "independent parameters". It also says that the model has several "fixed" parameters and several "...
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2
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Does neglecting dark matter solve the Hubble tension?
If the total mass of the universe is smaller than estimated by neglecting the gravitational pull of dark matter, the estimated expansion rate should be greater.
Does this consideration in the CMB ...
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What if gravitation was the only force? [closed]
This is a follow up of Interactions within constituents of dark matter .
I wonder about dark matter, and, naturally, compare it with our observable world.
If gravitation would be the only force acting ...
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110
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Is the amount of dark matter per galaxy the same as you look back through time (further away from earth)?
In the hope that it may inform us about the development/evolution (if any) of dark matter over time, are there any differences (eg. in structure or concentration) in the dark matter at large radial ...
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"Penrose Functional Degrees of Freedom" ( PFDoF) as a source of dark mass
In his book "Fashion, Faith, and Fantasy in the New Physics of the Universe" Sir Roger Penrose mention ( referring to his older works and specially Penrose-Hawking Theorem) the possibility ...
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3
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145
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Why doesn't frozen-out dark matter annihilate later during structure formation?
The so-called freeze-out of dark matter is based on a homogeneous description. However, in the later stages of the universe, where structures form, it seems very likely that the reaction rate would ...
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General Relativity "doesn't quite work" without dark matter?
I am taking an astrophysics course, and my astro professor said that "we need to introduce dark matter because Einstein's general relativity doesn't quite work without it".
I wanted to ...
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108
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Is Dark Energy Taking Over?
First question, trying to keep it simple 😃
Because it's constant it grows in magnitude as the universe expands, whereas normal matter does not? Is this accurate as far as we know?
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Galactic Rotation Curves
While researching rotation curves, I've noticed a variety of velocity behaviors in different galaxies. In some, the velocity decreases, in others, it remains relatively constant, and in some cases, it ...
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Theoretically, is it feasible for the dark matter density to be constant and homogeneous, as dark energy is, and the two to be related?
I know that currently dark matter and dark energy are separate things, not related and one not deriving from the other. But if both are included in a generalized gravitation theory, the picture can ...
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Does NFW profile work for any galaxy?
We use Navarro–Frenk–White (NFW) to calculate Dark Matter (DM) density. Can we use it for DM halo in any galaxy or is it used only for Milky Way (MW)?
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The 'core-cusp' problem for dark matter halos in larger galaxies
TLDR: Do observations of larger galaxies favour 'cuspy' dark matter halo distributions, as predicted by N-body simulations?
I've been trying to understand the 'core-cusp' problem for dark matter halos ...
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121
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Dark matter, MOND or flattened gravitational fields? [closed]
Could there not be a third variant to explain why e.g. long-distance multistar systems rotate faster than Newton's law of gravity suggests?
In addition to the Dark matter hypothesis and MOND then, ...
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151
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What if dark matter/energy did not exist?
What if dark matter and dark energy did not exist and were only due to a misinterpretation of the red shift of light or a measurement bias?
What would be the implications/consequences?
3
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106
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What happens to objects along spiral galaxy arms over long periods of time?
Observations of spiral galaxies reveal that objects within the same arm of a spiral galaxy move at around the same speeds, regardless of their distance from the center of the galaxy. Conversely, the ...
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24
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How much gravitational lensing do we see from the Milky Way?
I assume that the Milky Way has a dark matter halo just like any other. If that is the case, if we look at a huge part of our own galaxy, do we actually see the gravitational lensing effect? How ...
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93
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Event after big bang that cause dark matter [closed]
When the universe was formed by the Big Bang, what was the event that made some matter visible to us, while some became dark matter?
2
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2
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205
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Likelihood of MACHOs being the best candidate for dark matter
Massive compact halo objects ("MACHOs") include a wide variety of hardly detectable bodies such as brown / white / black dwarfs and black holes, to name a few. If we take into account the ...
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50
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Is the $σ8$ tension in the ΛCDM cosmology evidence that the amount of Dark Matter (DM) in the universe is increasing?
Strong evidence is provided by recent cosmological studies that “clumpiness” in the large scale structure (LSS), as measured by $σ8$, is decreasing (for example, “Hyper Suprime-Cam Year 3 Results…��, X....
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Why can't Dark matter be made up mostly of Neutrinos? [duplicate]
It's said that Neutirnos can only make up a tiny fraciton of dark matter.
So why can't Dark matter be mostly made up of Neutrinos?
Why can't there just be a huge number of them?
I suspect myself that ...
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40
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Could the energy emitted by galaxies contribute to the dark matter phenomenon?
I'm pondering a concept regarding the energy-mass conversion in the context of cosmology, specifically related to the light emitted by galaxies over billions of years.
Einstein's famous equation E=mc^...
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Reference: 1+1D paper-model representation of the Lambda-CDM cosmological model
I'm looking for a 1+1D (1 time + 1 space dimension) paper model of the current $\Lambda$CDM cosmological model; if possible, one which somehow respects the scales of geodesic spacelike distances at ...
3
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1
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119
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Could a fourth family of quarks and leptons account for dark matter?
In the early universe, could a family of quarks and leptons have formed an electrically neutral particle that is dark matter?
user361671
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1
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270
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How can black holes possibly drive accelerating expansion of the universe?
(Potentially too broad, but all my questions are related to the paper in question.)
Recently there was an article published in Astrophysical Journal Letters that claims black holes "contribute ...
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42
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Did galaxies spin differently 4, 5, 6 billion years ago?
Today I read that the Matter-dominated era ended 4 billion years ago, and now we're in the Dark Energy dominated era.
Obviously, light from galaxies far enough away would be from earlier in the ...
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143
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The slowing of expansion in the matter dominated era
On all the graphs of the inflation of the universe, the era dominated by matter is slowing the rate of expansion. With an intuitive explanation (for all you science communicators out there) could you ...
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50
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$\Lambda$CDM's observations and the universe's matter content
It's known that the current value of the universe's total density parameter $\Omega_0=1$.
According to the $\Lambda$CDM model, the current density parameter of baryonic matter $\Omega_P \sim 0.04$, ...
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103
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Have information bits a mass-energy equivalence? [closed]
Is it plausible (as some authors conjectured recently) that information is physical and that information bits are stored as a mass-energy equivalent in the universe, accounting for cosmic dark energy ...
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237
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Can gravitational effects from past matter that you're looking at lightyears away produce an incorrect image of it? [closed]
Can gravitational effects from past matter that you're looking at lightyears away produce an incorrect image of it?
During the period that light from distant matter is travelling back to earth, can ...
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2
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267
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Does anyone really know how dark energy/matter works?
If dark energy has no physical interaction with normal matter but it does interact with dark matter, wouldn't that cause an interaction with normal matter through its interaction with dark matter and ...
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1
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75
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How did neutrinos eliminated from dark matter? [duplicate]
I am reading "Dark Matter and Dark Energy" by Brian Clegg.
In Chapter 3 it's discussing about cosmic microwave background radiation and the elliptical shape
of early universe obtained from ...
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1
answer
1k
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The scale factor of $\Lambda$CDM as a function of time
From Friedmann equation for flat universe:
$$
\left(\frac{\dot{a}}{a}\right)^2= \frac{8\pi G}{3} ~~ \left( \rho_m + \rho_r + \rho_\Lambda \right),
$$
can we simply get the scale factor $a$ as a ...
- 395
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114
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How to test for possible negative mass of dark matter?
What is the phenomenology of how to test if dark matter has possibly a negative mass (WP negative mass) in particle physics experiments, cosmology or astrophysics?
I lately came across this ...
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137
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Could dark matter be just a gravitational effect of dark energy?
I'm wondering if we just looking at the two sides of the same coin and if there is actually a correlation of DM with DE?
Is it possible that DM just to be a gravitational effect (or an effect that ...
- 4,170
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19
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Dark matter and un-smoothness in spacetime [duplicate]
Since dark matter currently is only observable with its gravitational effects and nothing else can we theorize that dark matter is only non-smoothness in spacetime that has been there from the Big ...
4
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1
answer
190
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How do BAOs provide evidence for dark matter?
So far my understanding of BAOs is that they are a relic of the old universe formed by the freezing of acoustic density waves in baryonic matter as the universe entered the recombination epoch. These ...
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$Ω = ρ/ρ[c]$, so although near to 1, for an accelerating expansion $Ω$ must be below 1. What's its value?
$Ω$ is taken to have different components - ordinary matter, dark matter, dark energy. But because it is expressed in relation to the critical density for attractive gravity, it seems that omega is ...
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3
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662
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Why is the ratio of dark matter to normal matter larger in galaxies than the cosmic average?
There seems to be a discrepancy between the ratio of dark matter to normal matter in the Universe (about 5 to 1 according to $\Lambda$-CDM) and the ratio of the average dark matter halo mass to the ...
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Is there data regarding the large-scale density (mass/volume) of “dark matter plus ordinary matter,” as a function of time?
Here, large-scale means (conceptually) the known universe. Hopefully, the data runs from (perhaps somewhat after) the Big Bang until now. Pointers to such results would be appreciated.
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Gravitational binding energy as alternative to dark matter?
Pondering this question: Casimir effect and negative mass
and, in particular, the response of John Rennie "as the mass of any bound system is slightly less than the mass of its parts" I ...
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168
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Dark matter/dark energy in Einstein's equation as manifestations of entropy production
It is well known that pressure adds a contribution to the gravity sources in Einstein's equation. That contribution is unknown in Newton's theory. What about entropy itself, or more precisely the ...
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3k
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Is Dark Matter in Motion?
What is known about the motion of dark matter, especially in galaxies?
It seems as though a particular distribution of dark matter might be required to cause the very flat galactic rotation curves ...
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39
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About the spatial distribution of vacuum energy around strongly gravitating objects in the galaxy
We know that the distribution of vacuum energy is spatially uniform. But we also know that it couples to gravity.
Anything with energy, such as a beam of light is affected by the gravitational field ...
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167
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Could dark energy be explained via the use of a "gravitational charge"?
Could gravity be explained as the existence of a "gravitational charge", acting similarly to an electromagnetic charge but where like charges attract and opposite charges repel? A graviton ...
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37
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Axions approaching thermal distribution
I am reading Sikivie's paper on Axion Cosmology. I have the equation:
$$\frac{\mathrm{d}}{\mathrm{dt}}[R^3(n_a^{th}-n_a^{eq})] = -\Gamma R^3(n_a^{th}-n_a^{eq}) \tag{1}$$
where $R(t)$ is the ...
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Could quantum vacuum polarization increase GR frame dragging beyond the predicted values and therefore replace DM explanation of galactic rotation? [duplicate]
image source credits:David Butler
This anomalous speed rotation distribution of galaxies is today mainly contributed to Dark Matter.
However, since a definitive experimental measurement and ...
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