Questions tagged [redshift]

Questions related to the phenomenon whereby electromagnetic radiation (such as visible light) generated by an object moving away from an observer will have increase in wavelength (i.e. shifted toward the red end of the spectrum) once it reaches the observer.

Filter by
Sorted by
Tagged with
1 vote
0 answers
42 views

Angle to the line of sight

I don't understand this angle used in galaxy clustering. There is the line of sight and this angle to the line of sight which is not clear to me. Here is a transcript of a description from 1705.05442: ...
user avatar
0 votes
0 answers
48 views

How are CMB frame redshifts of galaxies corrected for coherent flows?

Say, if I downloaded the CMB frame redshifts of some galaxies from NED database, then what is the procedure to correct it for coherent flows? I'm using the SNooPy(snpy) Python package to analyze some ...
user avatar
1 vote
0 answers
12 views

Stellar connectivity for different cosmological redshifts

I'm creating models of stellar connectivity, for a range of cosmological redshifts (z=9, z=7, z=5, z=3, z=1, z=0, z=0.5). For that I'm doing the following steps: Sampling simulation sub-halos for ...
user avatar
5 votes
1 answer
124 views

How far away from us was Earendel star when it emitted the light that is just now reaching us?

From what I've read, the look back time is about 12.9 billion light years, and the current distance to the Earendel star is approximately 28 billion light years... How close to us was it when it ...
user avatar
  • 3,333
6 votes
1 answer
107 views

Declaring of 3C273 as a quasi-stellar object

I am currently reading A Brief History of Time and chapter 6 about black holes. Now, here it says He found it too large to be caused by a gravitational field: if it had been a gravitational redshift, ...
user avatar
  • 91
2 votes
1 answer
47 views

Radial velocity stability to spectrum shift calculation

I am engineer new to Astronomy and am trying to understand spec of an spectrograph (RV stability = 2m/s). There is a note in document saying "RV shift of 2 m/s is equivalent to a shift of the ...
user avatar
  • 23
1 vote
1 answer
41 views

Is luminosity distance related to both heliocentric redshift and CMB restframe redshift?

The luminosity distance $d_l=(1+z)r(z)$, where $r(z)$ is given by $r(z)=cH^{-1}_0\int_{0}^{z}\frac{dz'}{E(z')}$. When I use SN dataset Pantheon, I find there are two redshift $z_{cmb}$ and $z_{hel}$. ...
user avatar
12 votes
9 answers
4k views

Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

When we look in all directions, we see distant objects red-shifted, with the size of the red-shift correlated with the distance from us. As I understand it, the consensus among cosmologists is that ...
user avatar
  • 281
42 votes
3 answers
6k views

How did Hubble know the red shift difference between "moving away" and "old"?

My 9yo daughter is very into space at the moment and asked a question that my physics knowledge (6th form college, 20 years ago) is way too poor to answer. Her space book tells us that as stars age, ...
user avatar
2 votes
1 answer
82 views

Doppler Redshift vs. Cosmological Redshift ... or Both?

There are several existing threads on the difference between cosmological and Doppler redshifts. However, I don't see that any of them answered the question below. @pela gave the following example: &...
user avatar
  • 21
2 votes
1 answer
54 views

Intergalactic Lyman-alpha absorption for high redshift quasars (Gunn-Peterson effect)

This is a follow up to a recent question on SE asking about the apparent suppression of radiation shortward of the (red-shifted) Ly-$\alpha$ line of a quasar at redshift $z=6.53$. The general ...
user avatar
  • 2,314
1 vote
1 answer
63 views

Calculate speed of a galaxy with redshift

I was going through some old exercises but I could never figure out who to solve this one The hydrogen absorption line (656 nm) of the galaxy NGC 77 is shifted by 41 nm into the reddish wavelength ...
user avatar
  • 11
4 votes
2 answers
84 views

How to interpret this spectrum of the "new DESI Quasar at z = 6.53"; what causes the big edge at about 9150 Angstroms?

I'm not exacty sure why but Scitech Daily's Seeing Dark Energy’s True Colors: DESI Creates Largest 3D Map of the Cosmos includes the graphic and caption below. It indicates a quasar in a Hubble image ...
user avatar
  • 31.6k
3 votes
1 answer
85 views

Why is cosmological redshift treated as a different phenomenon to doppler redshift? [duplicate]

I understand that the expansion of the universe causes unbound structures to move apart from each other. This means that unbound structures have negative relative momentum due to universal expansion. ...
user avatar
  • 191
1 vote
0 answers
41 views

How to calculate radial velocity from redshift? [duplicate]

Ok, I know the question sounds silly, but please hear me out (at the very end it will probably still be silly though, albeit maybe differently). I'm trying to create a visualization of the galactic ...
user avatar
4 votes
1 answer
96 views

Are gravitational waves red-shifted?

Gravitational waves originate from significant distances. Presumably they are red-shifted the same amount as the galaxies they originated in. In the absence of gravitational “spectral lines”, can this ...
user avatar
  • 685
10 votes
2 answers
2k views

Can the gravitational redshift of our sun be measured?

How much of a wavelength change does our sun’s gravity cause in the light it emits? I imagine this could be measured by the shift in its spectral lines. And by extension, does the earth’s ...
user avatar
2 votes
2 answers
126 views

Could quasars be interior to the event horizon of a SMBH?

My question is prompted by suspicion of three current ideas in astrophysics: GR predicts a singularity at the center of a BH without regard to QM. quasar hyper-luminosity is caused by an acretion ...
user avatar
  • 29
3 votes
0 answers
83 views

How to remove redshift from galaxy spectra in Python?

Hello I extracted a spectrum from the central region of the 2D spectrum of the major axis from NGC 4697 (I just took a central row in the 2D data set, see this question for more information: How to ...
user avatar
  • 317
2 votes
1 answer
87 views

E(B-V) , the color excess between B and V bands, for galaxy at redshift 0

Following Mo et al. 2010 (page 479), the quantity $E(B-V)$, called the color excess between B and V bands, is equal to: $$E(B-V) = A_B - A_V = (B - V) - (B - V)_0 = (m_B - m_V) - (M_B- M_V)$$ where $...
user avatar
  • 51
8 votes
1 answer
121 views

How distant were the furthest currently-observable cosmic events when their currently-observed radiation was emitted?

(Edited for clarity. Thanks to James K and Connor Garcia.) This question about the most distant, observable cosmic objects made me wonder if we know the distance that was between us and them at the ...
user avatar
5 votes
2 answers
124 views

How does the hypothesis of the "inconstant Hubble constant" solve the current crisis in cosmology?

It was published in a paper more or less like two months ago. I'd like to know also if more accurate measurements are necessary to close the gap between the model of the universe and the data reported....
user avatar
4 votes
4 answers
321 views

Why do we see a cosmological redshift at all if space is not expanded in our solar system?

It is generally accepted that the large scale redshift of galaxies (as given by the Hubble law) is due to the expansion of the universe. According to this theory, the fabric of space itself stretches ...
user avatar
  • 2,314
2 votes
1 answer
50 views

Photometry templates -- what are the templates of?

Redshift measurements from photometric data can be determined using template-fitting (Cosmos website, SDSS photo-z). What does it mean to fit a template to determine redshift? What is the template of?
user avatar
  • 1,931
2 votes
0 answers
36 views

How to find the scale factor on given time in the future if initial distance between source and destination is known

Assume the received redshift $z$ of a photon is known. We then can calculate the initial distance (when the received photon was emitted), the light Travel Distance, the current Distance (proper ...
user avatar
2 votes
1 answer
515 views

Comoving Volume Calculation

Suppose I have data from an astronomical survey at redshifts in the range $z = [2,3]$. Suppose that, on average in this range, the data covers an area on the sky of $A=1$ $\mathrm{Mpc}^2$. How would I ...
user avatar
  • 85
2 votes
0 answers
43 views

Kaggle dataset for Photo-Z estimation?

I would like to use the dataset for this kaggle but the competition was private, is closed and I have been unable to contact anyone directly. The challenge is machine learning for photo-z estimation ...
user avatar
1 vote
1 answer
86 views

HR diagram x-axis (color) and redshift?

I've read several articles and watched some videos on the HR diagram, but no-one seems to mention the effect of redshift on the color of a star. Is there some calibration step that needs to be applied ...
user avatar
  • 113
5 votes
2 answers
266 views

Is there an equivalent of the red shift effect for cosmic rays?

I had read somewhere that light from very distant sources can be measured to be increasingly red shifted the further away the object is (due to cosmic inflation?). Suppose you had an object emitting ...
user avatar
2 votes
1 answer
54 views

When calculating absolute magnitudes of distant objects, do you use the light-travel distance or the comoving distance?

I want to calculate the absolute magnitude of GN-z11. Its light-travel distance is 13.4 billion ly (4.1 Gpc), its comoving distance is 32 billion ly (9.8 Gpc), and its apparent magnitude is $25.8$. ...
user avatar
0 votes
0 answers
50 views

Are there viable explanations for the red shift of distant galaxies other than the accelerated expansion of the universe? [duplicate]

I was told that photons lose energy (= increase their wave length) when moving away from mass and gain energy moving towards mass. Could this increased red shift of photons, originated a long time ago,...
user avatar
  • 111
1 vote
1 answer
75 views

Shouldn't the estimate of the universe's age be higher, not lower, after the attractive strength of gravity is taken into account?

From 'Fundamentals: Ten Keys to Reality', by Frank Wilczek : "Running the movie of cosmic history backward in our minds, we found the galaxies all coming together to meet at a definite time. ...
user avatar
  • 3,333
0 votes
1 answer
244 views

How do you calculate comoving distance and light's travel distance? According to the formulae below?

According to Wikipedia, Distance measures (cosmology), Comoving distance: $${\displaystyle d_{C}(z)=d_{H}\int _{0}^{z}{\frac {dz'}{E(z')}}}$$ Light-travel distance: $${\displaystyle d_{T}(z)=d_{H}\int ...
user avatar
  • 3,333
0 votes
0 answers
44 views

How long does it take for a galaxy (or other object) to disappear behind the cosmic sight horizon?

After looking at this question, I am wondering, how long does it take for a galaxy or other space object, to disappear from our view from the Milky Way due to the expansion of the universe? Assume GN-...
user avatar
2 votes
1 answer
112 views

Why are galactic nuclei yellow?

So we've seen millions of galaxies, and all of them have a bright, yellow nucleus. What is the cause of the yellowness? Is it because of aging stars, redshift from the SMBH, or something else?
user avatar
4 votes
0 answers
38 views

K-correction vs resizing photometric bands

Is there a difference between a K-correction (see Wiki https://en.wikipedia.org/wiki/K_correction) and simply "resizing" the bands, e.g. the 2-10 keV x-ray band, with the redshift? I've read ...
user avatar
1 vote
1 answer
753 views

How to find the distance between two galaxies from ra and dec and redshift [duplicate]

I have ra and dec and corresponding redshift of galaxies. I would like to calculate the distance between two galaxies. I did like this to find the nearest neighbour galaxies. Suppose I am trying to ...
user avatar
1 vote
1 answer
74 views

Question about redshift and effective gravity at the rotating neutron star surface

For a rapidly rotating neutron star, if consider the star as a sphere, redshift at the equator surface will be larger than at the pole. But if consider the star as an obsolate sphereiod (the ellipsoid ...
user avatar
  • 329
1 vote
1 answer
48 views

redshift in astrophysical plots [closed]

Why do astrophysicists often use redshift in plots? Why it is important to know how an astrophysical object evolves in function of redshift? I was seeing an "cosmological time per redshift ...
user avatar
0 votes
2 answers
77 views

is there a way to determine a distant galaxy’s speed relative to the Hubble Flow by measuring time dilation effects between there and this galaxy?

As I understand it there is a preferred frame of reference based on the velocity for the CMB and our galaxy is moving in relation to it (at about 600 km/s). I think this is how the Hubble Flow is ...
user avatar
2 votes
1 answer
69 views

Is there any way to distinguish the doppler redshift from a distant galaxy from the probably much greater cosmological redshift? [duplicate]

Is there any way to distinguish the doppler redshift from a distant galaxy, caused by its initial recessional velocity relative to this galaxy, from the probably much greater, cosmological redshift, ...
user avatar
0 votes
0 answers
42 views

What was the energy/wavelength/frequency of the CMB when first emitted/released?

Given the z redshift of 1089, and the temperature difference between then and now of about 1089, I tried scaling the ev, freq. and wavelength by 1089.... Is that right? I get a freq. of about 240 ...
user avatar
  • 3,333
1 vote
1 answer
40 views

Approximate formula to find velocity from cosmological redshift

From IOAA 2013 (Greece) Theory question no. 15, they stated that the approximate formula to find velocity from cosmological redshift is $$v = c*log_e (1+z)$$ and that it is often used by cosmologists. ...
user avatar
1 vote
1 answer
109 views

How to calculate the redshift of a line in a bunch of line spectra?

If in a spectra, there are many lines, mixed with gravitational redshift and non-redshift lines. For example, in this paper, they identify lines both redshifted and no-redshifted. Then how can i ...
user avatar
  • 329
6 votes
0 answers
210 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 ...
user avatar
3 votes
1 answer
79 views

Were radio spectroscopic observations ever used to first measure a distance successfully?

Usually, especially for an extragalactic object, its redshift is determined by optical spectroscopic redshift. But the angular resolution of early radio observations is poor and an optical counterpart ...
user avatar
  • 2,945
1 vote
1 answer
156 views

Intuitive explanation for why the Doppler effect (and red-shift) happens?

I was looking for an intuitive explanation as to why the Doppler effect happens. I haven't found any, but this is what I thought: -Waves emitted travel at a constant speed -The source emits a wave -If ...
user avatar
  • 201
0 votes
1 answer
59 views

Which redshift is used to determine the Hubbleconstant?

I think they measure cosmological redshift to use in the Law of Hubble-Lemaître together with the distance to calculate $H_0$. Is this correct, or do they use Doppler shift (too)? $H_0$ indicates how ...
user avatar
2 votes
2 answers
58 views

Is light emitted from a heavier body more redshifted than light from a lighter body?

Is light emitted outwards from, say, a region very close to a black hole more shifted than light with the same wavelength that began next to a less massive object?
user avatar
  • 743
2 votes
0 answers
60 views

Is cosmological redshift caused due to expansion of space or distance traveled by light?

If the universe wasn't expanding, would light still be redshifted after traveling some distance? Is there a way of being sure that it's the expansion that causes light to redshift and not just a ...
user avatar