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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.

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How can you calculate the distance to an object knowing its cosmological redshift? (without Hubbles law)

Given some redshift z, how do we find the distance using the cosmological red shift formula (and presumably the Friedmann equations)? a = 1/(1+z), and we can assume that omega_0 = 1. I know a ...
n014's user avatar
  • 51
-1 votes
1 answer
106 views

CMB redshift used to determine the difference in aging between the two inertial observers

If CMB redshift tells us our cosmological time dilation and we have two inertial observers in relative motion, who measure slightly different CMB redshift at the direction of their motion relative to ...
Nicram Alatiws's user avatar
2 votes
1 answer
43 views

Why would some sources in a cross-matched DESI/SDSS catalog have different spectroscopic redshifts?

I've crossmatched quasars from DESI DR9 and from SDSS DR16. When I plot the spectroscopic redshift from each of the individual catalogs for each source, I get: Naively, I'd expect the $z_{spec}$ to ...
Jim421616's user avatar
  • 2,620
2 votes
0 answers
67 views

Using prospector for jwst data

I am working with JWST data. I want to estimate the redshift of the sources I have identified with SEXtractor with the help of prospector. Can somebody guide me in this?
Walker's user avatar
  • 51
7 votes
3 answers
2k views

How do we work out the light travel time on a cosmic scale?

I just read this article in the AUSTRALIAN SKY & TELESCOPE magazine, Nov/Dec 2022 Issue 140, on P16, KEEP YOUR DISTANCE: How far away are the objects we see in the universe? And on P23: "And ...
Curious Cat's user avatar
0 votes
1 answer
92 views

Does a cosmological redshift occur within our local group, of galaxies?

I know that it is not supposed to be expanding but space is space and it is expanding everywhere else outside it so why not inside it too, and gravity just holds everything back. I suppose if it is, ...
Curious Cat's user avatar
2 votes
1 answer
134 views

Why are distant type Ia supernovae dimmer than expected?

Why are the (extremely) distant type Ia supernovae dimmer than expected? Relative to what? Their cosmological red shift? Well, what else. Please don't just say "Because the expansion is ...
Curious Cat's user avatar
-2 votes
1 answer
213 views

Shouldn't the Friedmann equation take into account the massive extra distance traveled during the time for gravity to travel across the universe? [closed]

I’ve got a question that has been bothering me for the past few years that of the few sources that are only somewhat related to this, none of them say anything about this should be wrong so I can’t ...
Gref's user avatar
  • 21
3 votes
1 answer
62 views

Why does a Decision Tree produce lines in photometric redshift predictions?

In this paper, the authors compare the speed and accuracy of various machine learning algorithms to produce photometric redshift estimates: Why does the DT regressor put the estimates into bands ...
Jim421616's user avatar
  • 2,620
0 votes
0 answers
34 views

Is the difference of redshift parameter z able to prove expansion is accelerating in flat FLRW universe model?

Sorry for my bad english, this is not my mother tongue. Recently, I've encountered a problem in cosmology class that is about FLRW universe. Assuming that the universe we inhabit is composed of non-...
ALLin's user avatar
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2 votes
0 answers
84 views

JWST Early Black Holes: Gas Collapsed To Metallic Hydrogen Core?

I was reading an article about early black holes found by JWST at Redshift 9. And saw that there was wonder at how large amounts of gas could collapse into a black hole as a theory. So my question is ...
WiFiSunset's user avatar
1 vote
1 answer
113 views

Finding an expression for the rate of change of Comoving volume with respect to redshift

I am trying to find the expression for the rate of change of comoving volume with respect to redshift, that is $\frac{\mathrm{d}V_c}{\mathrm{d}z}$. In this paper (Hogg, David W.), the comoving volume ...
noob anomaly's user avatar
8 votes
1 answer
445 views

The "k-effect"?

I'm reading some older materials which refer to something called the "k-effect". This was described as "hot stars in the Sun’s neighborhood are moving away from us in all directions, ...
Maury Markowitz's user avatar
2 votes
1 answer
96 views

How does doppler shift work for distant stars [duplicate]

I dont understand how you can look at the light from a star and say that it has been doppler shifted. For example a star emits a photon in the wavelength of 500nm and by the time it reaches earth it ...
Moiz khokhar's user avatar
2 votes
1 answer
159 views

Why does the velocity dispersion within a galaxy cluster decrease as a function of radius?

In the paper 10.1093/mnras/sty2379, there are plots showing the velocity dispersion as a function of radius. Focusing on the right-hand plot, non-merging normal clusters, intuitively why should the ...
ABC's user avatar
  • 53
18 votes
2 answers
3k views

Could we (Earth, Humanity, Solar System) be falling into a black hole?

With the expansion of the universe, all objects far away from us appear to be moving away (ie: exhibit Redshift). With distance, this acceleration / redshift also seems to increase (~73,000 (m/s) / (...
G. Putnam's user avatar
  • 297
1 vote
0 answers
87 views

If astronomers didn't know about redshift could we still determine the universe is expanding?

What other evidence is there for the expansion of the universe? Would the equations of physics look wrong without it?
user avatar
8 votes
1 answer
2k views

Is Webb or any near-future telescopes like ELT capable of observing redshift changes to confirm General Relativity?

The (Davis and Lineweaver (2003)) "Expanding Confusion" paper states that "the expected change in redshift due to cosmological acceleration or deceleration is only ∆z ∼ 10^(−8) over 100 ...
Glycoversi's user avatar
0 votes
1 answer
74 views

If a supernova explodes close to the centre of the milky way does its light get blueshifted by dark matter by the time it reaches the Earth?

Does the dark matter halo of the milky way cause most of the change in wavelength or is baryonic matter responsible?
user avatar
3 votes
1 answer
108 views

How can we estimate distance of galaxies by only redshift when there are other several factors other than distance to cause redshift

There are different factors for red appearance of different objects in the night sky. Two reasons which I know are Star red by nature Example: red supergiants They emit red light because of their ...
Prajwal D M's user avatar
5 votes
3 answers
3k views

How can redshifted light be detected?

I've been reading about redshifts and it got me really curious. Basically, I want to figure out how we know light is redshifted and what's the original emitted light. I found the following question ...
Matt's user avatar
  • 203
3 votes
3 answers
1k views

Could the redshift of all incoming photons be explained by a massive ring of distant masses pulling the sources of the photons away?

ChatGPT and wikipedia have informed me that the primary evidence for the theory that the universe is expanding is the fact that photons that arrive to our planet from all directions are being ...
Hisham's user avatar
  • 231
5 votes
0 answers
513 views

How far away must galaxies be before current telescopes can no longer measure how quickly they are rotating around one another or internally?

What is the distance limit and does it depend on the size of the galaxy and on noise and interference from gas clouds and our own Milky Way?
user avatar
2 votes
1 answer
149 views

Can the expansion of the universe cool my beer?

So the expansion of the universe stretches the light traveling through the void, as demonstrated by the cosmic microwave background radiation. These photons are lower energy than when they are ...
Yakk - Adam Nevraumont's user avatar
1 vote
1 answer
50 views

Interpreting the color of galaxies in deep field images

The HST produced some deep field images in mostly visible light, which contain thousands of galaxies that range in color from white to red (e.g. see here). I understand that the interpretation of ...
user1247's user avatar
  • 121
2 votes
0 answers
98 views

Empirical Constraints on the Time Evolution of Cosmological Redshifts

The standard model of Cosmology predicts that the redshift of a single source at fixed comoving distance varies with observation time according to $$ \dot z = \left( 1+z - \frac{H(z)}{H_0} \right) H_0....
jawheele's user avatar
  • 121
2 votes
0 answers
125 views

How does one estimate the mass of a galaxy using the Balmer break region?

I am currently reading the recent astrophysical paper "A population of red massive galaxies ~600Myr after the Big Bang'. In the first paragraph/abstract it mentions, "It has been difficult ...
shram's user avatar
  • 21
4 votes
1 answer
158 views

How does the Sachs-Wolfe effect confirm the existence of dark energy?

How is the Sachs–Wolfe effect and the existence of voids significant in providing physical evidence for dark energy?
user avatar
2 votes
1 answer
277 views

3d distance between the Galaxies inside the galaxy cluster

I am currently working on the dynamics of the galaxy cluster, so i am trying to get the distance between the galaxies inside the galaxy cluster from its centre. As a input i have RA , DEC and Z (...
Atul's user avatar
  • 41
4 votes
1 answer
186 views

What accounts for a Lyman-break for all wavelengths shorter than 91.2nm if the Lyman limit is the highest energy photon that neutral hydrogen absorbs?

From this description of Lyman-break galaxies, I don't understand how: ...radiation at higher energies than the Lyman limit at 912 Å is almost completely absorbed by neutral gas around star-forming ...
Rich McDaniel's user avatar
3 votes
0 answers
69 views

How do we know universe is expanding and not light slowing down? [duplicate]

We tend to take some things for granted, for example the light of speed is constant, but what if it isn't? How can we know that light is not slowing down at great distances for example, or that light ...
Dimitris's user avatar
3 votes
1 answer
333 views

Redshift distance proportionality at high Z and need for "mighty mouse" galaxies?

Allegedly supported by some evidence from the new James Webb space telescope physicist Eric Lerner has written an article that have garnered some attention. He writes that: "Put another way, the ...
Agerhell's user avatar
  • 457
6 votes
1 answer
457 views

What parameters of the Big Bang model will have to be adjusted to account for JWST's observations of highly redshifted galaxies?

There are a lot of claims, on YouTube at least, that the James Webb space telescope have found too many to old/highly redshifted normal looking galaxies to fit easily into the Big Bang model. One such ...
Agerhell's user avatar
  • 457
3 votes
1 answer
130 views

Minimum redshift for galaxies receding $\geq c$ when light transmitted

What is the minimum redshift for galaxies receding $\geq c$ when light was first transmitted that are visible today from Earth? Is that value the same as maximum angular size distance? This question ...
Sheldon's user avatar
  • 181
4 votes
1 answer
282 views

How is z calculated in red shift observations?

If z is calculated using the ratio between observable wavelength and emitted wavelength, how do we know the emitted wavelength of a star that is moving away from us? Wouldn’t we have to be at a ...
tomh's user avatar
  • 663
1 vote
1 answer
105 views

redshift puzzle

I have the central line of the spectrum of an elliptical galaxy (NGC:4697) and a template K-star. I have calculated the redshift z by computing the crosscorrelation function between the galaxy and the ...
trynerror's user avatar
  • 849
2 votes
0 answers
194 views

Plotting galaxies in 3-D

Suppose I have a catalogue of galaxies in a .dat file with each row representing information about a galaxy: right ascension of the galaxy, declination of the ...
peakcipher's user avatar
4 votes
0 answers
52 views

How does SDSS estimate photometric redshift of sources?

I'm looking through the data in SDSS DR 12: ...
Jim421616's user avatar
  • 2,620
2 votes
1 answer
689 views

Why is the CMB's redshift so high?

It is pretty well-established that the CMB was originally emitted around 380,000 years after the Big Bang, at a redshift of ~1100. The most distant known object is HD1, the light from which was ...
Max's user avatar
  • 284
1 vote
0 answers
62 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: ...
P. Ferreira's user avatar
1 vote
0 answers
123 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 ...
gautam bhuyan's user avatar
1 vote
0 answers
14 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 ...
8-Bit Borges's user avatar
5 votes
1 answer
319 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 ...
Kurt Hikes's user avatar
  • 5,297
6 votes
1 answer
135 views

Classifying 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, ...
Aveer's user avatar
  • 191
3 votes
1 answer
131 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 ...
Nirmala's user avatar
  • 33
1 vote
1 answer
208 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 the SNe dataset "Pantheon", I find there are two redshifts:...
user578569's user avatar
18 votes
11 answers
5k 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 ...
Brionius's user avatar
  • 341
42 votes
3 answers
7k 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, ...
Whelkaholism's user avatar
3 votes
1 answer
279 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: &...
Matt's user avatar
  • 31
3 votes
1 answer
163 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 ...
Thomas's user avatar
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