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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40
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8answers
7k views

Does matter accumulate just outside the event horizon of a black hole?

My understanding is that time slows and approaches stopping when approaching the event horizon of a black hole. I have seen this explained several places, including a brief explanation in the last ...
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1answer
2k views

How distances are measured in the Solar System, in the Galaxy, and in the Universe?

Distances in our universe can be calculated in several ways: Stellar Parallax Standard Candles Redshift How are these methods linked, and how they are actually used to calculate distances are ...
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2answers
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Where does the energy of light go, when it red-shifts?

When talking about the expansion of the universe, it is said that it can be proven by the red-shifting of light.(As we would need higher than lightspeed to get this redshift by the Doppler effect) I ...
15
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3answers
2k views

Is it possible to measure galactic red shift using consumer telescope equipment?

I was wondering if it would be possible to measure red shift from distant galaxies using consumer grade telescope equipment and spectroscopy filters. (like this one) I imagine it would require a ...
14
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3answers
7k views

Can the difference between a star and a galaxy which are point sources be detected?

Obviously a star would be a point source. A galaxy should be an irregular blob if close, but if it is far away then it would seem that a galaxy too would be just a point source. Given that the star ...
13
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4answers
1k views

Why are there so many seemingly blue-shifted galaxies in deep space

NASA released this image of deep space. The way light shifting vis-a-vis universe expansion is supposed to work is by making the furthest galaxies appear mostly red-shifted. But NASA's image shows ...
11
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1answer
2k views

How do we know if an object is redshifted?

I have some questions about redshift. I think that the first two hang on the last two, but feel free to point out anything you think I should know. How do we know if an object is actually redshifted,...
11
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1answer
1k views

How does gravity affect the wavelength of light?

If, hypothetically, me and my rocket powered flashlight were falling straight toward the center of a black hole. The flashlight is a few kilometers behind me in our travels toward the center of the ...
10
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2answers
2k views

Does the accelerating expansion of the Universe contradict Hubble's law?

Hubble's law gives a linear relationship between the distance to a galaxy and it's recessional speed. Observations of distant type 1a supernovae showed that their red shift (and therefore their ...
9
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6answers
901 views

Are there other proofs of the expanding universe apart from the redshift?

The theory of the expanding universe is so widely accepted, that the redshift is sometimes used as a measure of distance to far away galaxies. But is it still possible that the redshift is caused by ...
9
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1answer
2k views

In km/h, what actually is the “speed” of Andromeda away from us: cosmologically?

Andromeda is about 2.5 million ly away. Actually, in this universe, at what "speed" (in km/h) are two objects separating cosmologically - I mean strictly due to the "expansion of the universe" - if ...
8
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2answers
4k views

Which star / galaxy is moving away from us the fastest?

I know that we have measured the rate a lot of stars and galaxies move away from us using the doppler shift, and I know that the further a star / galaxy is the faster they accelerate away from us due ...
8
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3answers
743 views

Cosmological redshift vs doppler redshift

I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift. He ...
8
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1answer
447 views

Have we detected galaxies which have red-shifted beyond the visible light range?

According to this answer it is possible for galaxies' light to move beyond the visible frequencies due to redshift: ...
8
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1answer
242 views

Dark Energy Expansion

The new Cosmos extra features mentions that at about 6,771,500,000 years ago the universe began an accelerated expansion. How do we know this? What evidence do we have for this renewed and accelerated ...
8
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1answer
259 views

Why is the letter *z* customarily used to denote redshift?

What events led to the nearly universal acceptance of the letter "z" as the denotation of redshift? What did the letter originally stand for?
7
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2answers
696 views

Which galaxy is receding from the Milky Way the fastest? What is known of the mechanism behind its recession?

Galaxies are always in motion relative to the Milky Way. My question is, which galaxy is receding the fastest from our viewpoint? What is the theorised mechanism that causes this?
7
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2answers
405 views

Why do we have the cosmological constant?

Since the cosmological constant is not required to explain that the universe seem to be expanding, why do we have it? What other factors cause us to have that constant? Background: Without the ...
6
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3answers
476 views

Heavy star and redshift

A heavy star should look redshifted, due to gravitational time dilation. How is that incorporated into the calculations of distances to the stars, or is it negligible? How about an entire region of ...
6
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1answer
422 views

Where can I find a database of galactic spectra?

I was wondering where spectra of galaxies at various redshifts are to be found. I'm looking for ones that can be used to find the recessional velocity of the galaxy and eventually the Hubble Constant. ...
6
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2answers
1k views

Fingers of God effect for galaxy clusters

Galaxies that reside in galaxy clusters are know to have peculiar velocities that cause the Fingers of God effect. But what about galaxy clusters themselves? Do they also have peculiar velocites ...
6
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1answer
217 views

Might the universe be really small yet seem infinite from spherical reflections? [closed]

if a single source of light quite small, was placed somewhere inside a completely reflective sphere, quite large, what would the reflections look like from the light source's point of view within that ...
5
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4answers
409 views

Could a contracting Universe create the redshift effect observed by Hubble?

What if we just can’t see far enough and the redshift actually shows the galaxies speeding up towards a gigantic black hole to where everything is converging, repeating a cycle that took place ...
5
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2answers
311 views

Number Density of Dark Matter Halos

Is there a way to calculate the expected number density of Dark Matter Halos above a given mass, in a certain redshift range, and in a certain area?
5
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1answer
2k views

Does the universe expand at the same rate everywhere in the universe?

Specifically, I am wondering if some areas of the universe expand faster than other areas and whether the faster expanding areas diffuse the expansion through the slower expanding areas or does the ...
5
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2answers
234 views

Is there another explanation, apart from the doppler effect, for the redshift observed in distant galaxies?

On episode 10 of the original Cosmos TV series, Carl Sagan mentions that some scientist don't agree that the redshift observed in distant galaxies is evidence of the big bang, stating that probably ...
5
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1answer
682 views

Redshift quantization

A full disclosure to begin with: I'm a PhD student in mathematics and while I understand most of standard cosmological-astronomical terms and I've followed a one semester course on cosmology, I don't ...
5
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1answer
178 views

Can Hubble red shift be interpreted as time dilation?

Can we interpret the de Sitter universe as a spherical cosmic horizon null surface of finite radius, centered at Earth, and containing the Hubble volume of space where time is dilated and radial ...
5
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1answer
511 views

Is the expansion accelerating or Decelerating?

According to Hubble's Law, the farther a galaxy is, the farther it is moving away. But do we take into account the fact that we are actually looking in the past? For example, there are two galaxies A ...
5
votes
1answer
274 views

Sun's spectrum red shift

Does Sun's spectrum expose any red shift at all? Namely, the center of it's visible area (not due to limb effect). If it does, how much is it and does it comply with relativity theory or is it higher/...
5
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1answer
120 views

Red shifting galaxies

I am an amateur astronomer please correct if any of my understandings are wrong. We all know that from the Hubble's ultra deep field image the most distant galaxies which were created shortly after ...
4
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2answers
2k views

How Do we know about redshift?

Okay so scientists use the red shift to know that galaxies are moving away from us faster than light. How do we know that its not just red light from red stars. i mean most stars are in the infrared ...
4
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3answers
190 views

How do we measure distance in space?

I know that you can calculate the distance to another star for example, by using the phenomenon redshift to determine how much it has redshifted because of the expansion of the universe. But how do ...
4
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2answers
344 views

“True” motionlessness - red shifts and CMB

This is a question I asked years ago in an astronomy course, but to which I never got a straight answer. Please feel free to correct me if any of my assumptions here stray from facts. It goes like ...
4
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2answers
337 views

Can space-time expansion destroy light?

I know that light shifts from high frequency(like gama rays) to low frequency (like radio waves) when traveling throw a gravitational field, this is called red shifting. My question is: Is there a ...
4
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3answers
2k views

Do objects look larger the further away they are, beyond z=1?

I stumbled upon this text which illustrates and says: We find that as the object is moved to higher redshifts its angular size first decreases (as naively expected) but soon begins to increase ...
4
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2answers
16k views

How do we find the exact temperature of a star?

This is a very basic question, but I am a little confused. As far as I know, the temperature of a star is analyzed based on the color of the light it emits. So, if a star is moving away from us, then ...
4
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1answer
119 views

Dark energy and light red shifting

When light is red shifted from distant galaxies, the photons have lost energy. When dark energy pushes objects apart, those objects have gained energy from a larger gravitational potential. Is the ...
4
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1answer
238 views

Estimating galactic dust extinction for medium band filters

I have a set of medium-band filters and I would like to compute $A_{\lambda}/E(B-V)$ for each filter which are not reported in the literatures. The magnitudes of the objects in the photometry ...
4
votes
1answer
110 views

Interpretation and understanding of the relation for the photometric redshift in a given bin

In the context of photometric probe of surveys (like LSST), I need to understand the relation I have to use for photometric bins. Considering $p_{ph}(z_p|z)$ the probability to measure a ...
4
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2answers
75 views

Photometric redshift - empirical methods (machine learning)

I am currently learning about estimation of photometric redshifts with machine learning methods (or empirical methods in general). These methods use the knowledge about the photometry and the ...
4
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1answer
57 views

Photometric redshift [closed]

I have decided to do undergraduate thesis on "estimating photometric redshift" or something related to this using machine learning. Reading previous papers, I have come to know that work has been done ...
4
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1answer
101 views

Why is there no time in the distance equation using Hubble constant, red shift and speed of light?

So I had some problem and I think I solved it, then I began to dig out things around it and I found some equations using red shift etc. to get speed of the object in Universe relative to us and then I ...
4
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0answers
30 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 ...
3
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2answers
110 views

Why does the Supernova 2006cm give a very different value for the Hubble constant? Why doesn't it increase error bars for the Hubble constant?

The Supernova 2006cm has a redshift of 0.0153 which translates into a recession speed of 4600 km/s. It has a distance modulus of 34.71 which translates into a luminosity distance of 87 Mpc. This ...
3
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1answer
2k views

How do we know that light is redshifted/blueshifted and not the original light of a star/galaxy? [duplicate]

If a star/galaxy is moving towards us, then its light is blueshifted, and if it is moving away from us, then its light is redshifted. How do we exactly know that the color we are seeing is not part of ...
3
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2answers
182 views

How to disentangle a very distant star's relative velocity vs. redshift distance

We measure a star's relative velocity towards or away from us via its Doppler-shifted spectrum. This is also how we measure the distance of very distant stars: measuring the shifts in the spectrum ...
3
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2answers
946 views

Gravitational red shift vs Doppler redshift: Is the universe really expanding?

Is it possible that the redshift observed by Edwin Hubble is really from a gravitational redshift and the universe isn't expanding as he has predicted? What I think I know thus far is this: Redshift ...
3
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1answer
64 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 ...
3
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2answers
143 views

Does the expansion of the universe increase with distance?

I read something in a book the other day which has gotten me really confused. They were talking about the expansion of the universe, and if I understood it all, they said that the expansion of the ...