Why Does the Universe Appear Redder Than Expected?

[Chronos]

Well put nereid. Thanks for filling in the blanks.

 

[Mike2]

Well put nereid. Thanks for filling in the blanks.

What are you all trying to say... that the redshift is only due to dopler effects and maybe the local gravity well they come out of?

 

[Nereid]

What are you all trying to say... that the redshift is only due to dopler effects and maybe the local gravity well they come out of?

There's rather a lot of baggage being carried with the words we're using, and this may be interfering with understanding.

For instance, 'redshift'. For most of us this conjures up lines in a spectrum, e.g. an H LyA emission line observed at 250 nm instead of 121.6 nm. If it's an absorption line, no problems; if it's a band, OK too ... but what about 'line profiles', 'photometric redshifts', or 'Lyman break galaxies'? or the 'Integrated Sachs-Wolfe effect in the CMBR'?? How do we need to change our picture of what a 'redshift' is to be comfortable with these (and others)?

If we stick to 'emission/absorption lines/bands in the gamma/X-ray/UV/optical/IR/radio', then AFAIK three different mechanisms giving rise to observed redshifts have been clearly demonstrated*:
1) expansion of the universe, on scales ~ or larger than the local cluster/super-cluster ("Hubble redshifts"). As Chronos said, there are several very good sets of different observations for the reality of this mechanism; however, the value of the (local) constant - the 'Hubble constant' - has been difficult to nail down, and there's still a significant range that's consistent with the observational data
2) 'local' (relative) motion, within clusters and galaxies/globulars/gas clouds/etc - the Doppler effect we all know and love
3) gravitational redshift a la Einstein, Pound-Rebka, etc. AFAIK, there are very few direct observations of this (remember, we're looking at 'lines redshifted by the Einstein mass effect', not indirect observations such as high Doppler gas motions near a BH), and they (all?) find the gravitational redshift from line profiles rather than the lines themselves. http://www.lsw.uni-heidelberg.de/users/amueller/eng/astro_emeng.html

*I'm sticking to regions of space outside the Milky Way/Local Group; there's plenty of types of good redshift observations closer to home, but discussion of these is somewhat OT for this thread.

 

[shrumeo]

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

Then why isn't a black hole? The equation said if you have this much mass with this certain radius, you will be a black hole (or z -> infinity or whatever). So IS there a galaxy's worth of matter in a quasar? Is the quasar the radius of the solar system? What am I missing here?

Just incase you didn't know, GRBs are created by hypernovas with their jet directed at Earth.

I did know. That's my point. At one point we thought that they were coming from the edge of the universe and their luminosity was too high to be realistic. Are we assuming dumb things about quasars too?

 

[turbo]

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.

There is a very interesting grouping in the link you gave, Neried:

http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/35/

Snipped from the accompanying texts...Bottom center: Hubble has captured quasar PG 1012+008, located 1.6 billion light-years from Earth, merging with a bright galaxy (the object just below the quasar). The two objects are 31,000 light-years apart. The swirling wisps of dust and gas surrounding the quasar and galaxy provide strong evidence for an interaction between them. The compact galaxy on the left of the quasar also may be beginning to merge with the quasar.

I have looked all over the 'net trying to find evidence that someone has measured the redshift of the galaxy that is interacting with PG 1012+008, to no avail. Can anyone here help locate that data? Somebody must have done some redshift studies on the companions of that Hubble 20-QSO survey. There are too many interesting objects in the study to pass up the opportunity. The galaxy is well-separated from the quasar, so one would expect that its redshift can be determined with a better degree of certainty than those that have embedded quasars.

On a side note, the text characterizes the interaction as a "merger", as is customary with interactions of this type. There is no mention of the possibility that the quasar might have been ejected from the host galaxy, despite the fact that a number of quasars were found to be peacefully residing in relatively undisturbed galaxies. It is evident from the images that those quasars did not join the host galaxies via merger because the morphology of the hosts do not show disruption.

Here is a link that has been keeping me busy:

http://nedwww.ipac.caltech.edu/level5/index.html

On this page is a link for on-line atlases and catalogs, including Arp (northern and southern) and VV. Especially interesting are:

http://nedwww.ipac.caltech.edu/level5/Kuchinski/frames.html

Which illustrates differences in galaxy morphology in UV and optical images, and:

http://www.nrao.edu/astrores/HIrogues/RoguesLiving.shtml

which overlays HI maps over optical galactic images.

 

[meteor]

Here's the formula for gravitational redshift in scienceworld. Curiously, is different from all the others formulae showed in this thread
http://scienceworld.wolfram.com/physics/GravitationalRedshift.html

 

[shrumeo]

playing around with some numbers and plugging them into that eq. makes it seem more correct than the others.

dividing 1 by all the stuff under the root, then subtracting 1 makes for really small redshifts, even for really dense objects

the formula you found makes the grav. redshifts more dramatic

maybe someone better at math than me can mold the formula at the bottom here http://world.std.com/~sweetser/quaternions/gravity/redshift/redshift.html#red.escape

into a kiddie formula for the rest of us (well, ok, just me)