Why Does the Universe Appear Redder Than Expected?

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The discussion centers on the reasons behind the universe's observed redshift, suggesting that it may not solely be due to the Doppler effect from galaxies moving away, but potentially influenced by the mass of stars causing gravitational redshift. This raises questions about the mass distribution of distant stars compared to nearby ones, as well as the complexities of distinguishing light sources in space. Participants highlight that while gravitational redshift exists, it accounts for a small fraction of total redshift, with the primary cause being the expansion of spacetime. The conversation also touches on the challenges in understanding redshift and its implications for theories like the Big Bang and dark energy. Overall, the thread reflects ongoing debates in astrophysics regarding the nature of redshift and the universe's expansion.
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In my other thread I learned that gravitation red-shift does exists. Now I'm thinking of an explanation of why most of the universe seems "redder." Maybe its not because most of the stars and galaxies are moving away from us, but maybe its because some of the stars are massive enough to red-shift the light they emit to make it look like their moving away from us at great speeds.

I'm probably wrong but its just a thought.
 
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Not a completely ridiculous conjecture, although it does pose some problems. One of these would be the necessity of stars further away from us being more massive than nearby stars, since they are red shifted more. Since more distant stars appear quite similar in all other ways, it would be difficult to explain why they would be so much more massive than those in our immediate neighborhood.
 
i think the whole source of confusion and controversy in the red-shift discussion is from the fact that current theory pretty much assumes that the degree of the red-shift we see is due entirely to the Doppler effect

while some or most of the redshift from some or all objects should most definitely be attributed to that, why should we assume that a very massive object that has a very high redshift should be accelerating away from us faster than a less massive object with a lower redshift?

i think the reason so many people bash the big bang and inflation is because it seems to them that the theory is based an too many simplistic assumptions like redshift=distance=velocity and then because of this, exotic crap like dark energy/matter are apparently dreamed up to explain why observations are deviating from theory

maybe someone would like to educate us about this?
 
Well put shrumeo, you took the words right out of my mouth.
 
i think the whole source of confusion and controversy in the red-shift discussion is from the fact that current theory pretty much assumes that the degree of the red-shift we see is due entirely to the Doppler effect
Not true. The redshift due to the Doppler effect, that due to the peculiar velocity of an object, it's not the principal component of the total redshift observed. The principal component comes from the stretching of the wavelentgh by expansion of spacetime

Gravitational redshift indeed exist, as proved in the Pound-Rebka-Snider experiment, but it only accounts for a very small fraction of the total redshift. And not only the source can cause it, also other stars and bodies in the path from the source to us
 
Entropy said:
In my other thread I learned that gravitation red-shift does exists. Now I'm thinking of an explanation of why most of the universe seems "redder." Maybe its not because most of the stars and galaxies are moving away from us, but maybe its because some of the stars are massive enough to red-shift the light they emit to make it look like their moving away from us at great speeds.

I'm probably wrong but its just a thought.

One other aspect is the location of where one is viewing from, the 'line of sight'. Take our Sun, we see the light emited at a near constant frequency, we are always on the receiving end of its emissions, but when we gaze away from the Sun we do not see the light propergating away with a high Redshift signal.

If we look at a local nearby Star where our Suns light falls upon it, then it has to be Redshifted form 'Our' pespective viewpoint as it's light is moving away from us, so how do we distinguish light at far away locations as being 'totally' emited from the object in view?..when light from our Sun falls onto another celestial body, that light has to be Redshifted at 'the' location of the object being investigated, we do not observe light in flight through space, only at source or end-source.

So can we ask how much of our Suns light is falling upon any celestial object we view, and how much if any of this light adds to the Red-Shift signal of other celestial bodies?..how do we distinguish our Stars light from 'other' Stars light signals?
 
meteor said:
Gravitational redshift indeed exist, as proved in the Pound-Rebka-Snider experiment, but it only accounts for a very small fraction of the total redshift. And not only the source can cause it, also other stars and bodies in the path from the source to us

How do we know that gravitational redshift accounts for a very small fraction of total redshift? We know that clocks run slower the more deeply they are imbedded in a gravitational field - even atomic clocks. This was predicted by Einstein, and is confirmed by the offset needed to keep GPS satellites synched with ground-based clocks. How do we know that quasars are not near-singularities and that the light emitted from them is not redshifted by being emitted within a very strong gravitational field? This mechanism would at least explain how frequencies are redshifted without resorting to tired-light band-aids. There is a lot about redshifts that we do not know.
 
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turbo-1, I also believed that gravitaional redshifts could be important, but then i asked a question in this forum (i'm iron4 there), and JS Princeton, that is a knowledgeable person, answered this
http://www.badastronomy.com/phpBB/viewtopic.php?t=3636&highlight=gravitational+redshift+iron4

Note: Although JS Princeton seems to have been banned, and that surprises me very much, he used to be one of the leaders of the forum. Russ Watters also posts there, he can confirm that
 
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Ah, yes, the new one is that it's the expanding space elongating the light waves, i forgot

so, when did IBBT start? did it start with Hubble's observations or did it start with Einstein and his "cosmological constant"? or was one feeding into the other and we can't get an expanding universe out of our heads (where everything we see "points" to an expanding universe?)

So now, we have apparently said that the gravitational redshift isn't enough, and the Doppler redshift isn't enough to produce the redshifts we see, and it must be expanding space.

Was there ever a point when we thought that the Doppler shift was all we needed?
When was the transition made from all Doppler to some Doppler, some Compton, and mostly space expansion?

I think I want to start a thread about:
http://www.sciencemag.org/cgi/content/full/304/5675/1226b

which refers to soon-to-be-published results with implications to the age of the oldest stars (they could be older than 13.7 by)
 
  • #11
This is interesting. I had never heard of it before. Of course, we all had to learn the Lyman, Paschen, and Balmer Series in school.


from: http://cfa-www.harvard.edu/~jcohn/lya.html
Distribution of matter: The Lyman alpha clouds are formed by gas falling into gravitational potential wells of all the matter, not just the luminous matter. So they provide another tracer of dark matter.

They don't provide enough information here. Do they mean non-luminous matter (big clouds of gas, etc.), or the mysterious dark matter that's supposed to be most of everything?

this from: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A&A...329...30R
We study the evolution with redshift, from z ~ 5 to z=0, of the Lymanalpha forest in a CDM model using numerical simulations including collisionless particles only. The baryonic component is assumed to follow the dark matter distribution.

sounds like Aristotle's concentric spheres
 
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  • #12
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  • #13
Ah,
so a quasar is supposed to have a mass comparable to a galaxy
i will say a typical galaxy holds 10b stars,
let's just say our hypothetical galaxy has 10b solar masses
IIRC, a typical quasar has a radius comparable to the solar system
I will just say 30 AU

mass of sun = 2.3 x 10^33 g (from the Wikepedia page)
10b x this = 2.3 x 10^43 g
radius of 30 AU ~ 4.5 x 10^14 cm

plugging these into the equation above, I get a gravitational redshift from a typical quasar to be z=3.78 !

Am i wrong here?
 
  • #14
The emission source of quasars is thought to be infall of matter into a supermassive black hole. This occurs at a respectable distance from the event horizon: probably much greater than 30 AU. 10 billion solar masses is probably too large. There is no large gravitational redshift component in radiation emitted by supermassive black holes of known size, so no reason to think there it would be a major component of quasar emissions.
 
  • #15
Anyway, Shrumeo, I stated that that is the formula for a star! I don't know the formula for a quasar
If you scroll down the wikipedia page, there's a general formula for an spherical object, not necessarily a star. But given that quasars are really black holes (in General relativity volumeless pointlike or ringlike objects), the formula can't apply. Perhaps if you believe (like me) that black holes really have volume, you can try to apply this other formula...
 
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  • #16
The 'size' of a black hole is defined by the event horizon. All observable consequences [mainly Hawking radiation] end there. It occupies an observable [finite] volume of space in that respect. It is, however, an interesting feature. Due to quantum fluctuations the precise location of the event horizon is always fuzzy [always in a state of expansion or contraction]. If we apply this model to the concept of the universe as a hyper massive black hole [and it does contain similar features], we would be forced, at any given time, to conclude it is either expanding or contracting. Assuming that to be the case, time dilation effects would cause us to conclude that whatever state we happen to currently observe endures for an enormous period of time [by our clocks].

So this is the same as saying we exist in a universe with an event horizon radius of 13.7 billion light years. Anyone care to calculate the mass required to produce an event horizon of this size.. and see how it compares to the estimated mass of the observable universe? ... I'm feeling lazy at the moment.
 
  • #17
So what the general equation is saying is that M/R can never be more than
1.35 x 10^28 g/cm, otherwise you will have a black hole? Since as you approach that ratio z --> infinity.

Why am I told then, when I read things about quasars, that they have the mass of a galaxy (maybe I'm confusing luminosity) but the size of the solar system?
 
  • #18
The event horizon incompasses the area the size of the solar system not the singularity where the actual mass is held. And actual black holes don't have densities of 1.35 x 10^28 g/cm, that's just the threshold volume where after you pass it, all the matter is compressed down to a near point. So you can have a supermassive black hole with the mass of a galaxy but all the mass will still be all be in the central point.
 
  • #19
  • #20
shrumeo said:
So what the general equation is saying is that M/R can never be more than
1.35 x 10^28 g/cm, otherwise you will have a black hole? Since as you approach that ratio z --> infinity.

Why am I told then, when I read things about quasars, that they have the mass of a galaxy (maybe I'm confusing luminosity) but the size of the solar system?

It is often said that some quasars are as luminous as a thousand galaxies, even though the variability of the light output of such a quasar can limit its physical size to the diameter of our solar system. If quasars are at the cosmological distance suggested by their redshifts, this is the kind of awesome energy output that is calculated by relating their brightness to their perceived remoteness. If the extreme redshift of quasars is NOT due to their distance from us, but is caused by some other mechanism, they don't have to be as luminous (by many orders of magnitude).
 
  • #21
It is often said that some quasars are as luminous as a thousand galaxies, even though the variability of the light output of such a quasar can limit its physical size to the diameter of our solar system. If quasars are at the cosmological distance suggested by their redshifts, this is the kind of awesome energy output that is calculated by relating their brightness to their perceived remoteness. If the extreme redshift of quasars is NOT due to their distance from us, but is caused by some other mechanism, they don't have to be as luminous (by many orders of magnitude).

Redshift does not effect luminosity. Redshift chages the wavelegth of the photons, not the actual number of photons being emitted (luminosity) from the quasar.
 
  • #22
Implications of redshift...

Entropy said:
Redshift does not effect luminosity. Redshift chages the wavelegth of the photons, not the actual number of photons being emitted (luminosity) from the quasar.

I think you misunderstood me. I didn't say that redshifted objects are more or less luminous due to their redshift. The problem is that if redshift is interpreted as being an indicator of distance (as it always is, in the minds of conventional cosmologists), we are forced to attribute exceptional luminosity to quasars - as much output as 100s or even 1000s of galaxies.

Their apparent magnitudes are not great (most quasars are very faint and not even visible in amateur 'scopes like my 6" APO), but if they are at the distances required by a strict interpretation of redshift=distance, their absolute magnitudes have to be ridiculously high. Nobody has come up with a reasonable way to explain how an object with a diameter as small as our solar system can put out more energy than a thousand galaxies, each with billions of stars. Most cosmologists are willing to overlook this problem because the alternative (redshift can be intrinsic to an object, and not just cosmological) threatens the Big Bang, expansion, etc, etc. In short, if quasars are not at the distances assumed by their redshifts, the underpinnings of conventional cosmology are undone and many thousands of man-years of work will have to be re-examined and adjusted (if possible) or abandoned.
 
  • #23
turbo-1 said:
I think you misunderstood me. I didn't say that redshifted objects are more or less luminous due to their redshift. The problem is that if redshift is interpreted as being an indicator of distance (as it always is, in the minds of conventional cosmologists), we are forced to attribute exceptional luminosity to quasars - as much output as 100s or even 1000s of galaxies.
However, if redshift is a function of both Dopler effects and changes in the gravitational potential of the universe, then the velocity of distant galaxies is a function of distance to that galaxy and the mass of the universe. We would have one equation in 3 unknowns, and it would be impossible to solve for any of them.

So I have to wonder if redshift is effected by gravitational changes, then are the results of supernova observations still correct, and is the universe actually accelerating.
 
  • #24
There is other observational evidence that supports the premise that quasars are at the distances implied by their red shift -

1. Lyman alpha forest: inter-galactic non luminous gas clouds cause absorption lines in the spectrum of quasars. The number of absorption lines increase with distance, are less redshifted than emission lines of quasars, and do not appear in the spectrum of objects less distant than these gas clouds.
2. Gunn-Peterson trough: shortly after recombination [~300,000 years following the big bang], it was predicted remnants of the primordial soup would still floating around for a few billion or so years. These remnants would selectively block certain wave lengths in objects sufficiently distant. In the last year or so, the GP trough has been found in some extremely red shift distant [z=6+] quasars.
3. Type Ia supernova: Certain, extremely bright supernovas are useful as distance indicators because they have similar luminosity and their brightness decreases at a consistent and predictable rate. Type Ia supernova observed in galaxies at distances comparable to quasars have the luminosity and periodicity expected based on their own redshift, as well as the galaxies in which they occur.

There are additional indicators that remote objects, such as quasars, are at the distances suggested by their redshift, but, these are among the most compelling.
 
  • #25
I think you misunderstood me. I didn't say that redshifted objects are more or less luminous due to their redshift. The problem is that if redshift is interpreted as being an indicator of distance (as it always is, in the minds of conventional cosmologists), we are forced to attribute exceptional luminosity to quasars - as much output as 100s or even 1000s of galaxies.

Kay, my bad.

I have a question about redshifting over a distance. What actually causes light to redshift just by traveling large distances? The general background gravition? Or something to due with the expansion of the universe (something I also don't understant, why does that effect light at all)?
 
  • #26
Entropy said:
The event horizon incompasses the area the size of the solar system not the singularity where the actual mass is held. And actual black holes don't have densities of 1.35 x 10^28 g/cm, that's just the threshold volume where after you pass it, all the matter is compressed down to a near point. So you can have a supermassive black hole with the mass of a galaxy but all the mass will still be all be in the central point.


So, if there isn't a whole galaxy's-worth of matter in a quasar, where is all the energy coming from to give it the luminosity of many galaxies? I mean, if the thing were the size of the solar system, but putting out the power of a galaxy (or many galaxies) there should be the amount of matter comparable to a galaxy or so.

It's starting to sound to me like the old gamma ray burst problem.
 
  • #27
So, if there isn't a whole galaxy's-worth of matter in a quasar

I never said there wasn't a galaxy's worth of matter in a quasar.

It's starting to sound to me like the old gamma ray burst problem.

Just incase you didn't know, GRBs are created by hypernovas with their jet directed at Earth.
 
  • #28
Most quasars are too distant to see the host galaxy [which is another indicator they are extremely distant]. Some, however, are near enough to see their galactic halo.
 
  • #29
With respect to the mass of a quasar (and I'm referring exclusively to the black hole):it's tipically about 100 million solar masses
Compare it with the black hole of the center of M87: 3 billion solar masses

PS: Though the quasar SDSS J1148+5251 equals this last cipher
http://arxiv.org/abs/astro-ph/0303062
 
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  • #30
Chronos said:
There is other observational evidence that supports the premise that quasars are at the distances implied by their red shift -

1. Lyman alpha forest: inter-galactic non luminous gas clouds cause absorption lines in the spectrum of quasars. The number of absorption lines increase with distance, are less redshifted than emission lines of quasars, and do not appear in the spectrum of objects less distant than these gas clouds.
2. Gunn-Peterson trough: shortly after recombination [~300,000 years following the big bang], it was predicted remnants of the primordial soup would still floating around for a few billion or so years. These remnants would selectively block certain wave lengths in objects sufficiently distant. In the last year or so, the GP trough has been found in some extremely red shift distant [z=6+] quasars.
3. Type Ia supernova: Certain, extremely bright supernovas are useful as distance indicators because they have similar luminosity and their brightness decreases at a consistent and predictable rate. Type Ia supernova observed in galaxies at distances comparable to quasars have the luminosity and periodicity expected based on their own redshift, as well as the galaxies in which they occur.

There are additional indicators that remote objects, such as quasars, are at the distances suggested by their redshift, but, these are among the most compelling.
There are also a number of nice piccies of quasars at home inside galaxies (some examples); it may be that there are (difficult) observations of the redshift of the underlying galaxy in some of these cases.

Then there are those consistency points: the best model of a quasar also nicely matches observations of AGNs, Seyferts, ... (just turn down the volume); X-ray, gamma, radio, and IR observations of many kinds (e.g. 'diffuse X-ray background' becomes 'unresolved quasars, many invisible in the optical, but detectable in IR') ... none of these on their own does much, but together they form a nice, interlocking story ...
 

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