Unanswered Questions
264 questions with no upvoted or accepted answers
10
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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 ...
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7
votes
0
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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
7
votes
0
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315
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Gravitational eddies across the galaxy?
I read about natural gravitational eddies that travel in a wave that black holes have. They also have a strong magnetic field. Does those eddies follow magnetic field lines of the rotating black hole? ...
- 1
6
votes
0
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99
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How many galaxies are currently merging?
On the homepage of the galaxies research group at CfA SAO, it states, "Astronomers discovered that as many as 25% of galaxies are currently merging with others." They do not provide a ...
- 4,533
6
votes
1
answer
189
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Do narrow lines in the spectra of O- and B- type stars always indicate magnetic fields?
I was reading a paper on the differential emission measures of a set of hot O- and B- type stars. As the authors discuss in Section 3 (page 959), two stars, $\tau$ Sco and $\theta^1$ Ori C, have ...
CommunityBot
- 1
5
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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
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86
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Did the density wave theory for spiral arms take account of this phenomenon?
I came across this link. In it the author speculates that in the outer region of a galaxy, the spiral arms overtake the stars, and vice versa for the inner region. That means there must be a middle ...
- 403
5
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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 ...
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5
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0
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186
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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 ...
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5
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49
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What happens with a globular cluster when it passes through a galactic disc?
The orbits of globular clusters are crossing the disks of their galaxies, so they should sometimes pass through the disks. Are there any observed fluctuations in the clusters and in the disks ...
- 151
5
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62
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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
5
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0
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54
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Why Tidal Tails in Disk Galaxies, but not in Ellipticals?
Why do tidal tails result from only disk galaxies but not ellipticals.
I understand that tidal tails are results of gravitational interactions not strong enough to completely plunge out the material ...
- 1,452
5
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0
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719
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Which galaxy is closest to the center of the KBC void?
I was reading up on Bootes void and came across this list of the largest voids in the visible universe, and apparently the one we're in, the KBC void, is not only the biggest, but damned-near ...
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4
votes
0
answers
60
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Explanation for Planck 2018 temperature fluctuations strongest peaks
As it can be seen from Plank 2018 Cosmic Microwave Background temperature fluctuations data-
There are 3 sharp peaks at multipole expansions $\ell \approx 250, 550, 800 $. Also as multipole expansion ...
4
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0
answers
60
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How are plage regions related to the density of medium and velocity FeII ions?
During a literature review (abstract), I found that the intensity of FeII (298.5 nm) ions in the last solar minimum was higher than the two previous solar minima 21 & 22. The velocity of FeII ions ...
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