Unanswered Questions
201 questions with no upvoted or accepted answers
-6
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1
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What am I misunderstanding about the scale factor-redshift relation?
If the scale factor as a function of time represents or is equal to the average distance between the galaxies, then it increases altogether with the CMB redshift $z$, but it also must be equal to the ...
- 156k
-2
votes
0
answers
147
views
Universe age and cosmological time dilation throughout intergalactic space
Assuming the cosmological principle, universe has the same age and cosmological time dilation throughout intergalactic space. Why can't we use them as an indicator of synchronicity in two extremely ...
1
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0
answers
16
views
cross-matched SDSS-WISE catalog
Please where can I find cross-matched SDSS and WISE dataset for a machine learning project?
(Galaxy-star-qso classification task)
2
votes
0
answers
84
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
0
votes
0
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23
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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, ...
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3
votes
0
answers
41
views
Why MIT's Benjamin Rackham says "nearby ultracool dwarf SPECULOOS-3" would look "purplish-red, spotted, and flaring" from an airless orbiting planet?
May 15, 2024 MIT News article Newly discovered Earth-sized planet may lack an atmosphere includes the following:
“We can say from our spectra and other observations that the star has a temperature of ...
- 30.7k
0
votes
0
answers
35
views
Project Analog Hypothetical Planet
For my story Project Analog, I was wondering if a hypothetical planet (Let's call it Suria). It has the same size and conditions as Earth with the same axis, tilt, and rotation, as well as one moon. ...
CommunityBot
- 1
1
vote
0
answers
77
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
2
votes
0
answers
102
views
What would the Big Crunch theoretically look/feel like?
In the Big Crunch theory, the expansion of the universe reverses, resulting in all matter contracting into a single point. Imagine you are alive at the time of this event. What would the sky look like?...
- 29
2
votes
0
answers
174
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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
132
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 ...
- 30.7k
1
vote
0
answers
57
views
Fourier transform of the density fluctuation
There is a Fourier transform that I don't really understand in my textbook (p.218).
I have the following equation:
$$\ddot{\delta} + 2H\dot{\delta} -\frac{3}{2} \Omega_m H^2 \delta = 0
$$
Then using ...
- 101
2
votes
0
answers
34
views
Local anisotropies in the expansion of the universe and tidal forces...?
In the context of the large-scale structure of the universe, there can be local anisotropies (https://www.aanda.org/articles/aa/full_html/2021/05/aa40296-21/aa40296-21.html).
I understand from this ...
- 1,017
0
votes
0
answers
25
views
Deriving Faber-Jackson Relation from Milgrom's Law
I am reading Famaey & McGaugh 2011, a review paper on Modified Newtonian Dynamics. My question concerns bullet 3 in Sec 5.2, where the authors try to explain how Faber-Jackson Relation can be ...
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1
vote
0
answers
121
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Determining Time Based on Arc Seconds
So our arc day starts at 20°41'32 which is midnight (0:00) and ends 24 hours later at 21°42'42. According to my calculations it traveled 0 degrees, 59 minutes, and 30 seconds or 3570 arc seconds in 24 ...
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