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 increased in wavelength (i.e. shifted toward the red end of the spectrum) once it reaches the observer.

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4
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1answer
91 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 ...
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1answer
57 views

SDSS Image Download: Swarp returns all zeros

In the CASJOBS Server, I created the following query for galaxies(DR12) ...
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31 views

How to do logarithmic wavelength binning (in Python) in order to find redshift?

In Tonry and Davis (1979)(http://adsabs.harvard.edu/abs/1979AJ.....84.1511T), they formulated a cross-correlation method for extracting velocity redshifts. They bin the linear spectra into logarithmic ...
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1answer
42 views

How to identify component of velocity of a star from its red shift? [duplicate]

When a telescope observes a distant star, all it sees is the light being emitted by the star. Observing the wavelength of this light, we determine the velocity of the star. If the wavelength is red-...
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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 ...
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Q: Calculating the luminosity of a galaxy

I am currently working on a project on which I am calculating the luminosity of galaxies by using the SDSS data. They use a system of asinh magnitudes, and according to their website they use a system ...
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1answer
165 views

What is the time dilation less a magnetic field?

Does time dilation drop off like a gravity or does resemble a magnetic field model? Could a smaller body with a magnetic field have more time dilation then a larger body without and to what degree?
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1answer
31 views

Where a database of different z values of redshift can be found?

I was working on reshift details for various galaxies but do not know any database to find the z values given to redshift galaxies. Can anyone help?
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1answer
296 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. ...
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2answers
369 views

Quasar Redshifts

How can the gravitational redshift of a very distant quasar be distinguished from its cosmological redshift? Quasars are very massive objects,thought to be supermassive black holes,so therefore must ...
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2answers
130 views

Using emission lines to determine redshift of a quasar

I am attempting this past paper question and am not sure how to tackle this, this is not homework! :) The spectrum of a distant quasar shows two broad emission lines with observed wavelengths of ...
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2answers
91 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 ...
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3answers
151 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 ...
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How is “surface brightness dimming” derived from redshift in the NED extragalactic database

I have several questions regarding “Surface Brightness Dimming” in the “Quantities Derived from Redshift” section of the Nasa/ipac Extragalactic Database. As an example, please use quasar IRAS F08279+...
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Is it possible for redshift to be caused by light being somehow slowed down during travel? [duplicate]

In other words, is the assumption, that redshift is caused by universe expansion, definitive? Or are other theories still being considered? Could it be, that light is being slowed down by dark energy, ...
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2answers
238 views

Is blue light not traveling faster then red light in space?

I just can't understand why light and other massless particles are not traveling at different speeds? Gravity effects anything with a mass but light has no mass but a black hole, and weak lensing ...
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1answer
97 views

How to correct observed flux densities for redshift

Say I have a spectrum of a galaxy at a redshift $z$, in flux density units of erg/s/cm^2/Angstrom. I'd like to recover the spectrum (in the same flux density units) at z=0, i.e. at its rest ...
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98 views

If objects don't move when the universe expands, how can the expansion result in redshift?

I am approaching this topic from a layman's perspective and view this as a logic puzzle, but when someone tries to get me to accept the logic, I'm never convinced by their arguments. According to ...
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30 views

Relationship between photometric colour and redshift, part two

In the graphs in my previous question here, there are negative-sloped regions as the colour-z relationship oscillates. So if I look at how the I-W2 and W3-U colours change with redshift, as I've done ...
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1answer
35 views

Relationship between photometric colour and redshift

In this paper, the authors describe the theoretical relationship between photometric colours, particularly in Figures 1 and 6: Since the colour is the difference between two magnitudes, and the ...
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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,...
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6answers
486 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 ...
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2answers
147 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?
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2answers
73 views

Can I take logarithms of magnitudes (which are already log) [closed]

I'm investigating the relationship between the magnitude of quasars in various wavelengths, and their redshift $z$. I've found that if I take the $log$-$mod$-transform ($L_{mag}$) of the magnitudes, ...
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2answers
56 views

Wavelengths for observed objects — emitted or observed?

The WISE craft (Widefield Infrared Survey Explorer) surveys the sky in 4 wavelength bands; 3.4, 4.6, 12, and 22 $\mu$m. When it's observing an object with an estimated redshift (given by $z = \frac{\...
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1answer
198 views

At what speed does something have to travel away from us for it to red shift enough that it becomes invisible to the human eye?

Are there stars, galaxies etc that we cannot see because they are traveling too fast and their spectrum is shifted below our visible range? From what I understand, red shift is caused by stars and ...
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2answers
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Do other supercluster like Laniakea also get pulled by the Great Attractor?

I'm not sure, whether there is any other observable super cluster like our local one, Laniakea, and if they do exists, do they also get pulled by the Great Attractor? I am a little confused about ...
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0answers
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Do gravitational waves have distinct bands or parameters from which a source redshift can be inferred? [duplicate]

In optical astronomy, much (most?) electromagnetic radiation is emitted at well defined frequencies, and this can be used to infer a redshift for the source, and hence its recessional velocity, age, ...
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2answers
118 views

How far away is this galaxy?

Arp 299 is in the news, with most sources reporting it as 140 or 150 million light-years away. But what kind of distance is this? The paper which is trhe source for the news item has Supplementary ...
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1answer
266 views

Question from Introduction to Modern Cosmology by Andrew Liddle

The exact question goes like this: In the real Universe the expansion is not completely uniform. Rather, galaxies exhibit some random motion relative to the overall Hubble expansion, known as their ...
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0answers
51 views

How can you estimate distance of an object by its redshift? [duplicate]

Is there a way to take the red shift of an object and, from that, calculate a rough estimate of its distance from us (in parsecs, preferably)?
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2answers
547 views

Approximate conversion of redshift 'z' to a time and/or distance, when reading papers?

I'm looking for some form of "rough and ready" formula to convert between redshift z value, years since BB, and distance, so that when I read an astronomy paper and it discusses an event that occurred ...
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1answer
45 views

Photometric redshift

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 ...
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1answer
114 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/...
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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 ...
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2answers
280 views

How does space time differ within a galaxy?

Not the same question but is similar to other marked duplicate. How much time dilation does the center of a galaxy can exist and sustain human life from our point of view? What would a day equal to ...
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3answers
289 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 ...
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2answers
146 views

Is there any way to tell which way is the next universe? [closed]

Is there a observable void outside our universe that can give a clue on how far the next on is? How many universes can surround ours? What does a universes gravity well look like?
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Can the shedding of radiation of stars contribute to the red-shift of the universe?

The sun is losing mass(1.5cm per year) by emitting radiation and the orbits of the planets are widening because of the weakening gravity of the sun. Are most of the stars shedding mass via ...
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2answers
240 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 ...
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1answer
67 views

Does wavelength affect redshift caused by the metric expansion of space?

Does wavelength play a role in cosmological redshift? Do we see certain wavelengths affected less by expansion or notice any delay in arrival of certain wavelengths? How accurate are any observations?...
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168 views

Redshift observation at different wave length

Can one star be observed at different wave length show different redshift ?
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1answer
280 views

How to shift AGN x-ray spectrum to rest frame from

I have limited information to shift a spectrum (in the x-ray 0.5-10 keV bandpass) at redshift z=2 to rest frame. I have a plot of normalized (photon) counts s$^{−1}$ keV$^{−1}$ by energy (keV), and so ...
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1answer
46 views

relative distance and right ascention

The redshift-distance relation is $cz=H_0d$. So if we have $z$ we can calculate $d$. But is there a way to calculate or covert or write this $d$ in terms of right ascension (RA) and declination (DEC) ?...
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1answer
743 views

Understanding The Turnover Point of Angular Diameter Distance

I am trying to get a better understanding of cosmological distances, in particular the angular diameter distance which I have also seen referred to as angular size distance. What I am looking for is ...
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2answers
288 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 ...
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1answer
263 views

Approximating density of hydrogen in [observable] universe

Let universe be completely made from hydrogen. And also we have redshift $z= 6$. with Hubble constant $H_{0} = 2.1941747572815535\times 10^{-18}\:\mathrm{s}^{-1}$. We also know that density of the ...
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1answer
220 views

Question about Hubble parameter (Hubble constant) and measuring it

I see this question in "An introduction to modern cosmology - Andrew Liddle - Wiley Publication": In the real Universe the expansion is not completely uniform. Rather, galaxies exhibit some ...
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1answer
147 views

How long will it be until the nearby groups of galaxies are receding at speeds faster than light?

And subsequently how long will it be until we can never see them again?
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1answer
738 views

How to convert theoretical template spectrum from luminosity density to flux density units?

I'm working with galaxy spectral templates (e.g., Bruzual & Charlot 2003) which seem to always come with y-axis units of $L_{\odot}$/A and x-axis units of Angstroms. Thus the y-axis is a ...