Unanswered Questions
201 questions with no upvoted or accepted answers
12
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0
answers
218
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Estimating the tangential and cross component of the galaxy's shear using Gnomonic projection
I would like to know how I can estimate the tangential and cross component of the galaxy's shear using Gnomonic projection
of the right ascension and declination the galaxies relate to the center of ...
- 5,636
10
votes
0
answers
211
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How well conserved is etendue in extreme gravitational lensing scenarios?
This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description:
Light from the background galaxy circles a ...
- 30.7k
8
votes
1
answer
186
views
What is the history of the average pressure, density, and temperature of the matter in the universe over time?
This question is inspired by this more specific question where Cerelic wanted to know if conditions were suitable for liquid water to exist during an epoch when the characteristic temperature of the ...
- 61
7
votes
0
answers
256
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Get the expression of probed volume between 2 redshifts
1) I can't manage to find/justify the relation (1) below, from the common relation (2) of a volume.
2) It seems the variable r is actually the comoving distance and not comoving coordinates (with ...
CommunityBot
- 1
5
votes
0
answers
70
views
Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow?
Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow? I mean is it mandatory for a jet to be emitted from an accretion disk?
If so, then why?
...
- 2,169
5
votes
0
answers
127
views
Explain as simply as possible how the Sunyaev-Zeldovich (SZ) effect is used to estimate the Hubble constant
The Sunyaev–Zeldovich effect (SZ effect) is useful in determining the Hubble constant because it is independent of the cosmic distance ladder. This effect occurs when CMB (cosmic microwave background) ...
- 30.7k
5
votes
0
answers
79
views
How did pressure evolve in the (early) universe?
I am trying to derive how the cosmological pressure $p(t)$ evolved over time in the universe, especially in the radiation and matter dominated epochs. There are some very nice explanations how $H(t)$ ...
- 5,636
5
votes
0
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88
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Significantly blueshifted Lyman-$\alpha$
Lyman-$\alpha$ line in galaxies is notably known to show a double peaked profile, mainly due to its scattering in a moving medium, see e.g., the very recent Matthee et al. 2021, The X-SHOOTER Lyman-α ...
- 30.7k
5
votes
0
answers
104
views
How to place an observer in a cosmological simulation
Suppose I have a cosmological simulation with points in xyz space at a certain redshift in a cube like this:
And I have these for many cubes of different redshifts say from z=0 to z=2. Now I want to ...
- 326
5
votes
0
answers
185
views
What are some good books/online resources for astronomy problem sets?
I am currently studying for the international olympiad for astronomy and astrophysics (the syllabus can be found here: https://www.ioaastrophysics.org/syllabus/). I am currently using Carroll Ostlie's ...
- 147
5
votes
0
answers
126
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Does the cosmological principle apply to the entire universe?
Some cosmological models assume that the universe is isotropic and homogeneous and that is also flat and infinite. If the universe is infinite now it was infinite immediately after the big bang. If ...
- 91
5
votes
0
answers
62
views
Strength of core-envelope coupling in stars
For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope?
I understand that the core-envelope boundary is only (...
- 4,533
4
votes
0
answers
70
views
What does it exactly mean for spacetime to have no global symmetries?
Are there spacetimes or metrics with no global symmetries? Spacetimes/metrics with no global Poincaré, Lorentz, diffeomorphism, CPT, translational and gauge invariances?
And if there are, what does it ...
- 1,017
4
votes
0
answers
97
views
Why is the latest Webb discovery of early-age universe considered so important?
The past week, news were flooding of an unexpected discovery of James Webb Space Telescope. In many articles it is mentioned that cosmologists cannot explain the formation of galaxies of this ...
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4
votes
0
answers
70
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If the universe is a closed spacetime structure, can we assign a center of mass to it?
If we envision the universe like a balloon but in 3D, is it possible, in general, to assign a of global center of mass?
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