All Questions
31
questions
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21
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About redshift and distant objects observation
I did a few Time&Length dilation factor calculations. This is for a distant clock away from any field and a clock on Earth on the equator with the moon passing over clock coordinates, the factors ...
0
votes
2
answers
43
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Stars that have fairly high gravitational redshift and calculation of their surface temperature by Planck emition spectra?
How high can the ratio between gravitational redshift and planck emition spectra be depending on the mass of the star so by how much this gravitational redshift could elongate the Planck spectra of ...
- 2,255
1
vote
2
answers
129
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Is cosmological redshift associated with recession velocity when the light left or when it arrived?
Is the cosmological redshift $z$ associated with the recession velocity when the light left, when it arrived, or something in-between?
user300520
2
votes
1
answer
35
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Advantage of a single large telescope over many small ones for optical/infrared spectroscopy?
In a thought experiment where we would like to do optical/infrared spectroscopy on distant galaxies, and in which we would like to increase as much as possible the resolution of the spectroscopy (...
- 1,109
1
vote
3
answers
109
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Why do we See Black Holes?
The image of things falling into a Black Hole stays frozen on the event horizon forever. So how is it that we don't see the image of a dying star where a Black Hole formed?
We see the black, with an ...
- 61
2
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0
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81
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Keck versus Webb: discrepancies in the redshift measurements of the galaxy GN-z11 (the most distant galaxy discovered with the Hubble Space Telescope)
Two years ago Nature Astronomy published a paper based on measurements from the Keck Telescope stating that the redshift of the galaxy GN-z11 (discovered by Hubble) is:
$$ z=10.957 \pm 0.001 $$
Source:...
- 507
1
vote
1
answer
82
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Calculating distance to galaxies seen through a telescope
When we see a galaxy through a telescope, say the James Webb telescope, it is said we see a galaxy as much as about 10 billion light years away. But 10 billion years ago we were much closer (because ...
- 137
1
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2
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141
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Too many low redshift galaxies in NED database
When using the NED database I found there are too many galaxies with very low redshift (Near zero). I used NEDs search by parameters function to find all galaxies within Z=0 to Z=.03 redshift. I did ...
- 67
1
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1
answer
161
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If the redshift of CMBR is 1100 is then possible find an object as a protogalaxy at e.g. redshift 100?
If the redshift of CMBR is 1100 is then possible find an object as a protogalaxy at e.g. redshift 100? If the telescope 'James Webb' can 'look' very far should it detect some very distant objects ...
- 2,255
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2
answers
42
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When we measure our distance from a very distant astrophysical object image do we input its past location and our present location?
When we measure our distance from a very distant astrophysical object do we input its past location and our present location? Please take a look on the picture where our past location is A1 and the ...
- 1,815
1
vote
1
answer
185
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Cosmological redshift due to recession speed or expansion of space?
I am somewhat confused regarding the factors that cause cosmological redshift.
This wiki states that the amound of cosmological redshift coming from let’s say, a star, is calculated by
$$z=\frac{H_0 D}...
- 471
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0
answers
160
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What is the meaning of "current" CMB rest frame or the CMB rest frame at redshift $z$?
As I know that the definition of the CMB rest frame is the comoving frame of the plasma emitting CMB. And the anisotropy of CMB is due to the velocity difference between the earth frame and the CMB ...
- 11
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2
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576
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What's the reference/original wavelength while calculating redshift?
Measuring redshift is one of the ways of analyzing distance in astronomy, since the redshift of an object is caused by the expansion of space between us and the object, the more space there is between ...
- 338
0
votes
1
answer
142
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How astronomers estimate the redshift of galaxies clusters?
I don't understand how astronomers estimate the redsfhit of a cluster. As far as I understand a cluster of galaxies is something really "big", so I expect that different galaxies in the ...
- 429
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1
answer
183
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What is spectral redshift resolution of observationally detected damped Lyman Alpha clouds?
What is the spectral resolution, $\Delta z,$ when detecting damped Lyman alpha systems at different epochs, $z \sim 0-3,$ through current and/or future observational instruments? And is this redshift ...
- 115