All Questions
Tagged with cosmology astrophysics
339
questions
-2
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32
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What is the energy density of gravitational fields around neutron stars? [closed]
The field strength of gravitational fields around neutron stars is extremely high. This would lead to an extreme negative value for the energy density. But if an absolute negative energy density is ...
-1
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0
answers
43
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Should luminosity distance be $0$ at $z=0$?
I am working on coding up the luminosity function for blazars but I have ran into a problem. In equations 1-3 of this paper https://arxiv.org/abs/1912.01622 they state that the flux can be broken down ...
- 57
2
votes
1
answer
76
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Can glueballs and bosons survive indefinetely in space (forming structures)?
I have been recently interested in looking for possible structures (ranging from clumped structures like "stars" to diffuse clouds of gas or halos) made from standard model-particles other ...
- 2,466
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53
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Can there be structures made from neutrinos that can have angular momentum?
Would it be possible to eventually have structures made from neutrinos somewhere in the universe, as it is indicated in this question (Are neutrino stars theoretically possible?), like halos of ...
- 2,466
3
votes
1
answer
97
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Does the Kardashev Scale have any practical application?
As the question states: are there any practical applications of the Kardashev Scale?
- 1,058
4
votes
1
answer
139
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Supressing proton and neutron decay?
I was wondering whether the decay of neutrons and protons (if they happen to be able to decay, as it is predicted by some GUTs) could be avoided in some cases.
Let's begin with neutrons:
In principle ...
- 2,466
0
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0
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33
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Turnaround radius being increased in fast collapsing regions?
In the context of formation of large-scale structures, there would be a turnaround radius where expanding matter would detach from the Hubble flow and start to collapse (https://www.aanda.org/articles/...
- 2,466
1
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2
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59
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Interplay between gravity and cosmic expansion causing collapse of large-scale structures?
As far as I understand it, in the context of large structure formation, the interplay between gravity and cosmic expansion can cause certain anisotropies in voids that can make them collapse (https://...
- 2,466
2
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48
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Voids blueshifting CMB photons (in certain cases)?
I have some questions about this interesting work (https://iopscience.iop.org/article/10.1086/517603/pdf) where the authors analysed the effects of voids in the CMB radiation (particularly through the ...
- 2,466
0
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0
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13
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CMB anisotropies due to moving clusters/voids?
Apparently, there is an effect where a moving overdensity/underdensity (or an object, e.g. a galaxy, moving in an overdensity/underdensity) that is going through an evolution of its gravitational ...
- 2,466
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20
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Relativistic Fluid Equation - Density Perturbations in Cosmology
While I am deriving the relativistic fluid equation for the radiation component I am getting an extra term like $\vec{v} \cdot \vec{\nabla}P$ where $\vec{v}$ is the velocity and $P$ is the pressure.
...
- 3,122
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Can the integrated Sachs-Wolfe and the Rees-Sciama effects have any influence on matter?
CMB photons can be affected by the expansion of the universe through the linear integrated Sachs-Wolfe effect (ISW) 1 and the non-linear ISW effect or also called Rees-Sciama effect 1.
In particular, ...
- 2,466
1
vote
0
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61
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Bunch-Davies initial condition
I have the Mukhanov-Sasaki equation in terms of $Q(t)$
\begin{align*}
Q''(t)+3HQ'(t)+k^2Q/a^2+\left(3\phi'(t)^2-\phi'(t)^4/2H^2+2\phi'(t)V_\phi/H+V_{\phi\phi}\right)Q=0,\ u=aQ
\end{align*}
and also ...
4
votes
1
answer
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 ...
- 351
1
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2
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129
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Is cosmological redshift associated with recession velocity when the light left or when it arrived?
Is the cosmological redshift $z$ associated with the recession velocity when the light left, when it arrived, or something in-between?
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