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Questions tagged [dark-matter]

Questions about astrophysical observations, experimental searches, and theoretical models related to dark matter and its quanta.

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Could dark matter be radiation pressure? [closed]

I watched Stephen Wolfram on a podcast explaining this idea last night. He said that dark matter could be explained as "spacetime heat". My contention is that stars and black holes trap a ...
Eschaton Magazine's user avatar
1 vote
2 answers
52 views

Dark matter detector experiments above ground?

Most of the dark matter detectors I hear about are built below ground to shield from cosmic rays. One problem I see with this is what if the ground is also shielding dark matter from interacting with ...
Voltage Spike's user avatar
2 votes
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88 views

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....
vengaq's user avatar
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Gravitational waves created by quantum fluctuations as the source for dark energy and dark matter [closed]

Two generally accepted principles: Quantum fluctuations generate gravitational waves (Axion monodromy and inflation by Albion Lawrence, Brandeis/NYU) Gravitational waves can be absorbed (Numerically ...
VMT's user avatar
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Galaxies rotations speeds questions

We accept epic gravitational lensing effects around invisible supermassive black holes, but do we consider possible gentle lensing effects in huge galactic structures observations ? Do we take time ...
olivierlambert's user avatar
2 votes
3 answers
2k views

Is there a Dark Matter Paradox?

According to this preprint, The Importance of Being Symmetric: Flat Rotation Curves from Exact Axisymmetric Static Vacuum Spacetimes, spiral galaxies possess flat rotation curves without assuming Dark ...
timm's user avatar
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2 votes
1 answer
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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 ...
Kevin Kostlan's user avatar
3 votes
2 answers
339 views

Why are forces superimposable in Classical Mechanics? Does this also apply in higher theories like General Relativity and Quantum Mechanics?

In classical mechanics, forces are treated as vectors and are added linearly. Is this principle to be treated as an axiom or is there some underlying principle from which this is derived? And given ...
Vivek Kalita's user avatar
2 votes
1 answer
397 views

Contribution of dark matter to running of physical constants

I read that "essentially everything in the Standard Model impacts the running of every physical constant in the Standard Model. So, if there is even a single particle missing from the Standard ...
Jtl's user avatar
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1 answer
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What if dark matter and anti-matter collided? [closed]

Considering we know both dark matter and antimatter can interact via gravity, just like regular matter, then that means the two can gravitationally interact. However, since dark matter does not ...
Quantum Wonder's user avatar
3 votes
1 answer
250 views

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% ...
luckchen jammy's user avatar
1 vote
1 answer
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Does dark matter have mass?

When trying to understand what dark matter is, it is helpful to know that some properties of it can already be derived from various observations, such as, it only interacting via gravity and no other ...
Quantum Wonder's user avatar
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2 answers
72 views

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 ...
Ben Sprott's user avatar
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Equivalence of axion to fermion couplings

In order to solve the Strong CP problem through the axion, we introduce the axion-gluon coupling $$ \dfrac{a(x)}{f_a} \text{Tr}\, G\tilde{G}.\tag{1} $$ In a similar fashion, we may introduce the axion-...
Gabriel Ybarra Marcaida's user avatar
1 vote
1 answer
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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 "...
tparker's user avatar
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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 ...
Manuel's user avatar
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Group velocity, phase velocity and signal velocity for axion like particles

In dark matter models of axion-like particles (ALPs), sometimes we get the field $$\phi=2\phi_0\sin(m_\phi c^2 t/\hbar)\cos(k_\phi x)$$ This is like an stationary field with amplitude $\phi_0$ (in m/s ...
riemannium's user avatar
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Yang-Mills mass gap caused by gluonballs or because dark matter WIMPs?

Yang-Mills quantum field theory predicts the existence of the lightest massive Bosonic (i.e. integer spin) particle. This massive Boson will be much lighter than the $W$ and $Z$ Boson and therefore ...
Markoul11's user avatar
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Dark matter Thermal average cross section expansion

In many papers and books, including paper written by P.Gondolo & G.Gelmini in 1991, COSMIC ABUNDANCES OF STABLE PARTICLES: IMPROVED ANALYSIS, it is well known that for non relativistic gas, you ...
hwan's user avatar
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2 answers
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Is there an spherical symmetric Einstein vacuum solution which has circular orbits with flat velocities? Or a proof that it cannot exist?

The Schwarzschild solution shows decreasing velocities with larger orbits - and needs help from dark matter or MOND to explain galaxies. Apparantly no Einstein vacuum solution with flat velocities is ...
Tantal181's user avatar
15 votes
3 answers
2k views

What's the argument(s) against dark matter being "normal" baryonic dust?

So I just finished watching "dark matter is not a theory". An understanding I gleaned from it is that dark matter is observed from the discrepancy between the amount (or perhaps energy? in ...
user151841's user avatar
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Why are dark matter and dark energy favoured over changes to our physical models? [closed]

I am instinctively skeptical of the existence of "dark matter" and "dark energy". Together, they strike me as being analogous to luminiferous aether -- something that was invented ...
spraff's user avatar
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1 vote
1 answer
125 views

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 ...
Gyro Gearloose's user avatar
3 votes
3 answers
1k views

Is Dark Matter really invisible? [duplicate]

From what I understand dark matter is called dark since it cannot be seen in the universe. My question is does it have to be invisible, as in to not interact with light ? Could it be that dark matter ...
Jonathan's user avatar
4 votes
1 answer
110 views

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 ...
Zinn's user avatar
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0 answers
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What is dark matter? [duplicate]

My friend asked me about dark matter and started saying that it is likely to be another world made up of things we say dark matter and energy said that quantum fluctuations may be the cause of dark ...
Mathematical gyan's user avatar
-3 votes
1 answer
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If we are sure dark matter is not modified space producing gravity can we spot an object deacceleration while moving through a dark matter cloud?

Can a moving object deacceleration caused by interaction with enviroment be measured while the object passes through a region populated by dark matter?
Krešimir Bradvica's user avatar
1 vote
1 answer
77 views

"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 ...
kakaz's user avatar
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1 vote
3 answers
144 views

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 ...
Bababeluma's user avatar
6 votes
2 answers
2k views

Attraction between dark matter

Why does dark matter not attract other dark matter in space, and form a giant structure?
Super Vision's user avatar
3 votes
4 answers
2k views

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 ...
Thomas Moore's user avatar
2 votes
3 answers
1k views

Why isn't the "Dark Matter" in the Bullet Cluster supermassive black holes?

I've seen several videos that claim that the Bullet Cluster is evidence for Dark Matter. The general idea is that the gas is trapped on one side of the collision and the light-bending "Dark ...
The Shepard's user avatar
0 votes
3 answers
108 views

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?
Wileyo's user avatar
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3 votes
0 answers
117 views

Is shape dynamics capable of explaining dark matter?

I recently got introduced to the incredibly fascinating subject of Shape Dynamics: for example see https://arxiv.org/abs/1409.0105 Shape Dynamics uses conformal three-dimensional geometry to build up ...
MartyMcFly's user avatar
1 vote
3 answers
100 views

Interactions within constituents of dark matter

Inspired by Are the visible matter and dark matter separately segregated? I wonder if the constituents (I don't say particles, as we don't know) have actions and forces among themselves, that we ...
Gyro Gearloose's user avatar
0 votes
1 answer
60 views

Are the visible matter and dark matter separately segregated?

I am having difficulty in visualising dark matter. Dark matter does not interact electromagnetically. Dark matter is inferred gravitationally. However it is not clear whether dark matter is present ...
SacrificialEquation's user avatar
0 votes
0 answers
35 views

Can dark matter be isolated from baryonic matter?

The above is an image to test Verlinde's emergent gravity theory (2016, https://arxiv.org/abs/1611.02269). The research team observered galaxies and masses beyond, used gravitational lensing (y-axis) ...
Koen de Jong's user avatar
-1 votes
1 answer
152 views

Which of Newton's shell theorems applies to a galaxy?

From this question I gathered that Newton came up with two sets of shell theorems, one for hollow spheres and one for solid. It was also said we should use the version inside a solid sphere to model ...
Livid's user avatar
  • 870
0 votes
1 answer
48 views

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 ...
mahsum's user avatar
  • 19
0 votes
1 answer
134 views

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 ...
Rahim's user avatar
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1 vote
2 answers
171 views

How can I estimate the dark matter density for some specific galaxies by using the rotation curves?

I have rotation curve data (radius vs rotational velocity) for some specific galaxies. How can I estimate the dark matter density for those specific galaxies by using the rotation curves? Or is there ...
mahsum's user avatar
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0 votes
0 answers
20 views

Scalar Axion Field Amplitude Calculation in localised laboratory / Earth

This question concerns the paper "Axion Dark Matter: What is it and Why Now?", in the Appendix A.3 regarding equations related to the Axion Field. It states that by the Friedmann Equation, $$...
Avis Yu's user avatar
0 votes
0 answers
53 views

Invisible decaying dark photon

I am interested in invisibly decaying dark photon to the dark sector. Let's assume the particles in dark sector are dark photon ($\gamma_D$), dark matter (DM) , and long lived particle scalar ($\phi_D$...
PhysicsStudy's user avatar
0 votes
1 answer
45 views

When calculating the amount of missing mass in a galaxy due to dark matter, do cosmologists take into account local effects of gravity on time? [duplicate]

If I understand correctly, massive objects cause time dilation, and so time seems to pass more slowly for observers closer to a massive object than those who are farther away. Do cosmologists take the ...
Amber Lily's user avatar
1 vote
1 answer
183 views

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)?
Peyman's user avatar
  • 11
1 vote
0 answers
82 views

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 ...
H-QM-W's user avatar
  • 11
2 votes
0 answers
48 views

Slope in interaction strength vs mass for QCD axion

The theory models of QCD axion, i.e. those who solve the strong CP problem, all have a prediction that follows a band with a slope in the space interaction strength vs. axion mass. (1) What does cause ...
Stefano Barone's user avatar
1 vote
1 answer
121 views

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, ...
Lehs's user avatar
  • 521
1 vote
1 answer
45 views

Flat galaxy formation in a spherical dark matter halo

The dark matter halo of our own galaxy is assumed to be spherically symmetric. This sounds reasonable, since dark matter interacts gravitationally. However, stars in our galaxy are on a flat disk. ...
SD11's user avatar
  • 171
0 votes
1 answer
23 views

Can outer star be captured by a more distance galaxy due to dark matter?

Imagine of an outer star lies between 2 galaxy cores with identical matter & dark matter distribution. If the outer star lies closer to galaxy core 1 and farther to galaxy core 2, the dark matter ...
Hantarto's user avatar
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