Questions tagged [cosmology]
Questions about the origin, history, evolution and fate of the Universe.
42
questions
1
vote
1
answer
56
views
What exactly does $k\sigma$ mean in astrophysics and cosmology?
In statistics, $\sigma$ or $1\sigma$ is the standard deviation. For the normal distribution, approximately $68\%$ of the values lie within $1\sigma$ range, $95\%$ within $2\sigma$, and $99.7\%$ within ...
- 441
2
votes
0
answers
83
views
Would we know if the universe was rotating?
I was wondering what we would observe if the universe had a small rotation. My conclusion was that galaxies on the equatorial plane of the universe would be slightly more redshifted than galaxies than ...
- 373
8
votes
1
answer
574
views
References about neutrinos getting clumped in "structures" in the future?
I was wondering whether (standard model) neutrinos could form clumped structures (like halos perhaps). The problem with this is that neutrinos have a very light mass, have a great speed and do not ...
- 1,017
1
vote
1
answer
110
views
Does the lower value of the Hubble Constant predicted by the Planck Satellite and now confirmed by Wendy Freedman invalidate the idea of dark energy?
Is the dark energy part of the Lambda-CDM model (the 'lambda') still necessary if the value of the Hubble 'constant' is lower than that predicted by Adam Reiss and collaborators when they examined ...
- 5,177
0
votes
0
answers
22
views
Is the hypothetical '(Don) Page curve' of evaporating black holes equal in time, so to speak, on both sides of the curve?
I have heard that Hawking radiation is slow at first, but rapidly increases when the black hole becomes much smaller... (I forget the formula...)
Does that mean that the second half of Page's curve, ...
- 5,177
7
votes
1
answer
129
views
What exactly is a 'gravastar'? How is it different from a 'regular' black hole?
The Wikipedia article on gravastar says that it has a 'regular' black hole metric (Schwarzschild, I presume?) on the outside, but a de Sitter metric on the inside....
What exactly does that mean?
Don'...
- 5,177
0
votes
2
answers
79
views
How can $\Omega_m<1$ indicate an infinitely expanding universe?
I was reading up about the cosmological density parameters $\Omega_m. \Omega_{rel}, \Omega_{\Lambda}$ corresponding to total matter(baryonic+dark), relativistic particle matter and dark energy. I ...
- 779
5
votes
2
answers
495
views
White dwarf supernova luminosity
I understand that the mass limit for a white dwarf is 1.4 solar masses, and therefore approaching it would cause a white dwarf (type Ia) supernova, and thus it is a standard candle. I understand this ...
- 173
1
vote
0
answers
75
views
What is Helix Nebula made up of?
The Helix is a planetary nebula, the glowing gaseous envelope expelled by a dying, sun-like star. Helix nebula consists of two gaseous disks, how they are formed or which material is present in it.
- 53
4
votes
1
answer
538
views
Can an astronomer fully work remotely? [closed]
My question today is addressed to those astronomers who have quite a lot of experience working remotely.
In general terms, the answer to the question includes the following elements: the range of ...
- 853
0
votes
0
answers
75
views
How can I convert luminosity from [erg/s/Hz] to [erg/s]
I have the dust-corrected luminosity in the Ks band in the unit erg/s/Hz. I want to convert it to erg/s. I would like to know which method is correct:
$L[erg/s]=L[erg/s/Hz]\times(C/\lambda)$
$L[erg/s]...
3
votes
1
answer
167
views
A couple of questions on Hawking radiation
Black holes progressively evaporate due to the emission of Hawking radiation just outside their event horizon primarily in the form of photons. However, there is a small probability that they emit ...
- 1,017
2
votes
1
answer
107
views
Earth-Moon receding-approaching cycle?
I made the following question in an another more informal forum of discussion on physics:
My question comes after reading this article: https://www.coastreporter.net/in-the-community/the-moon-is-...
- 1,017
2
votes
0
answers
159
views
What happens at the edge of a finite and "bounded" universe?
So far, we know only about two types of universes: Infinite and finite universes (Unbounded edition).
In an infinite universe, there is no edge. Because well, an infinite space doesn't have an edge. ...
- 2,668
3
votes
0
answers
128
views
What are the loopholes in recent claims that dark energy is not necessary?
I read an article on spacechatter about recent work that eliminates the need for dark energy in explaining observations. The pertinent quote from that article is
“The study’s findings confirm that ...
- 131