Unanswered Questions
238 questions with no upvoted or accepted answers
10
votes
0
answers
211
views
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
7
votes
0
answers
256
views
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
answers
315
views
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
answers
99
views
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
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
86
views
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
votes
0
answers
88
views
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
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
49
views
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
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
5
votes
0
answers
54
views
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
votes
0
answers
719
views
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 ...
- 37.3k
4
votes
0
answers
60
views
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
votes
0
answers
107
views
Reasons for extremely high number density of galaxies at low redshift
I am currently analyzing the SDSS data especially in the extremely low redshift area, in order to measure the cosmological statistics. What I mean by extremely low is z<0.1. One peculiarity that I ...
4
votes
0
answers
32
views
How are shockwaves used to study magnetic fields of merging galaxy clusters?
Recently i read an article about how a shockwave 60 times larger than milky way galaxy is generated.When these shockwaves interacts with magnetic field, radio waves are emitted. I wanted to know how ...
