Unanswered Questions
114 questions with no upvoted or accepted answers
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What are You 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 ...
1
vote
0
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16
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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
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0
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84
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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 ...
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3
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0
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41
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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
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0
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35
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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
2
votes
0
answers
102
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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
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0
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34
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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
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25
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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
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0
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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 ...
- 2,349
0
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0
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66
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Flux from the Sun on the Earth using the Stefan-Boltzmann law
What is wrong with this computation, plase? I am getting the result of 4291.65 W m^{-2} instead of 1361 W m^{-2}. Thank you very much
...
- 555
0
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46
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Consistent values for density of galaxies between degree squared and steradian
I have a table of densities of galaxies :
Expected number density of galaxies for photometric survey per unit area and redshift intervals, $\mathrm{d} N / \mathrm{d} \Omega \mathrm{d} z\left[\mathrm{...
1
vote
0
answers
24
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What would be the new Equation of motion if the magnetic field's origin is shifted from the origin of a co-rotating spherical polar coordinates?
The equation of motions due to the dipole magnetic force of a planet in a frame corotating with the planet and origin at the centre of planet assumed to be sphere components wise are given as below:
\...
- 145
0
votes
0
answers
33
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How to plot different curves in the same polar cordinates in matplotlib?
I tried to plot the paths of particle of different sizes in the same polar coordinate using the code given below using matplotlib. somewhat like this:
Instead I got this plot:
while the path for ...
- 145
2
votes
0
answers
70
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How is an index of n=0 possible for the Lane-Emden equation?
I was recently showing that an index of $n=0$ for the Lane-Emden equation results in constant density throughout the star. However, in my calculations I had to use the constant $\alpha$ which can be ...
- 106
1
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0
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37
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What is value of charge by mass ratio (q/m) for a spherical micro charged particle with surface potential 6 volts in S.I units and in e/amu units?
In Liu and Ip (2014),The Astrophysical Journal, 786:34 (8pp), the value of q/m is derived as follows :
"for a dust grain with radius 'a', from $\phi = \frac{4\pi q}{\varepsilon_0 a}$ we have $\...
- 145
0
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0
answers
60
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Crop a FITS file in shape of another
I have a FITS file, let us say file A. I have another FITS file, file B. File B has a smaller footprint than file A. I want to crop file A in shape of file B. How do I go about doing that?
- 304
0
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0
answers
50
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calculating mass of galaxy from luminosity
A very elementary question, just to make sure I got this thing right.
Suppose we are given that the mass to luminosity ratio of a galaxy is $2 \frac{M_{\odot}}{L_{\odot}}$.
Let us say, that the ...
- 221
1
vote
0
answers
99
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Formula for "gravity assist"
I am familiar with the concept of "gravity assist" by which a space probe or other object, passing near a moving planet, can pick up some of the planet's orbital velocity.
I presume that ...
- 511
2
votes
0
answers
60
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What could these LMC objects in this color-color diagram be?
I have performed a color-color and colour-magnitude plot of various sources detected in an LMC image (JWST NIRCAM F200W, F150W and F115W filters). I then also queried SIMBAD to collect relevant ...
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1
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94
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Is there such a thing as a map that shows the current (not observed) positions of celestial objects?
As I understand it, maps of the sky and three-dimensional maps of the universe all show the observed positions of celestial objects.
Are there any maps that show our best guess at their current ...
- 111
3
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0
answers
68
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Gravitational recoil with stars/planets...?
When two black holes are merging, the resulting merge can be ejected if one of the black holes had less mass than the other one, so the gravitational waves emitted by both of them is unbalanced, and ...
- 1,017
1
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0
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222
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Typical astronomical and astrophysical problems in various programming languages
As a rule, work in the field of observational astronomy and astrophysics requires knowledge of such programming languages as: C/C++ and the principles of OOP, MPI, CUDA. Sometimes additional ...
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2
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0
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34
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Could rogue planets with cold nucleus have winds or water currents/waves due to the planet's rotation?
Are there any types of wind or waves caused and produced only and exclusively by a planet's rotation? Not influenced by the planet's rotation, but produced solely by it?
In the case of waves, are ...
- 1,017
0
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0
answers
50
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What are the primary astrophysical implications of a proposed mass of about 11 M⊙ for the SN 2023ixf progenitor?
The abstract of the arXiv preprint SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova (itself recently "discovered" in the observatory) ...
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0
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0
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42
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Trying to understand how to properly implement this equation to a healpix map
So i am working on reproducing a paper (Secrest, N. J., von Hausegger, S., Rameez, M., Mohayaee, R., Sarkar, S., & Colin, J. (2021). A test of the cosmological principle with quasars. The ...
- 20k
2
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0
answers
61
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Is there an equation that can give position of a satellite around a parent body as a function of time?
I’ve been looking into this lately, and most sources I have used solve this problem numerically. I was thus wondering if there is a proper equation to solve for position without numerical, especially ...
- 201
2
votes
0
answers
101
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Conversion of 1D plot in 3D plot gives different physics
I am to track the path of a particle due to Lorentz force of the planet magnetic field, assuming there is no gravitational force on it.
The equation of motion due to Lorentz force in rotating ...
- 145
1
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0
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108
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What exactly IS a "Domain Wall"?
A Domain Wall is an "topological defect" and a 2-dimensional singularity. They are widely theorized to exist throughout the universe, but none have been detected yet. I'm having trouble ...
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1
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95
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Stellar structure equations - mass continuity
Out of the four stellar structure ODEs, I would like to understand why the mass continuity equation was named this way. It reads
$$ \frac{dm}{dr}=4\pi r^2\rho \tag{1} $$
and I understand what it means,...
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2
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0
answers
255
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Abundance of an element Xi in mass fraction from its abundance by number
How can I calculate the expression of the abundance of a given element Xi in mass fraction from its abundance by number Ni/NH, where log(NH) = 12 is the abundance by number of hydrogen?
I've tried the ...
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