Redshift Effect on Absorption/Emission Lines

[Drakkith]

Is the width of spectral emission/absorption lines stretched in either cosmological or doppler redshift?

 

[cepheid]

Generally speaking, no.

Let's take a gas cloud as an example. The width of the line is determined by the random motions of the individual emitters. The whole gas cloud may be moving away from you. However, some emitters are moving slightly faster away from you and some are moving slightly slower away from you. This is because of the velocity dispersion (the spread in velocities around the mean motion of the cloud).

The result is that, even after accounting for the redshift, not all emitters emit at the same wavelength, leading to a spread in the range of wavelengths that constitute the line. This phenomenon is called "Doppler broadening."

In summary, the overall motion of the cloud towards or away from you leads to an overall shift in the location of the central peak of the spectral line. The spread in velocities present due to the random thermal motions of the gas particles (which depends on temperature) determines the width of the line.

Thermal broadening is just one mechanism of broadening. Turbulent motions within the gas cloud can do it too.

 

[Drakkith]

Understood. Thanks Cepheid!

 

[Chalnoth]

Is the width of spectral emission/absorption lines stretched in either cosmological or doppler redshift?

Well, if you think about it, the lines have to be broadened by the exact same amount as the wavelength is lengthened.

Imagine, for a moment, that some source emits light between 100nm and 101nm. If that source is at a redshift of 1, then the 100nm lower part will be redshifted to 200nm, while the upper wavelength of 101nm will be redshifted to 202nm, changing a 1nm width line to 2nm width.

I don't think that there are any additional effects on top of this that would broaden the lines further (though interaction with matter can do that).

 

[cepheid]

Well, if you think about it, the lines have to be broadened by the exact same amount as the wavelength is lengthened.

Imagine, for a moment, that some source emits light between 100nm and 101nm. If that source is at a redshift of 1, then the 100nm lower part will be redshifted to 200nm, while the upper wavelength of 101nm will be redshifted to 202nm, changing a 1nm width line to 2nm width.

I don't think that there are any additional effects on top of this that would broaden the lines further (though interaction with matter can do that).

Yeah I missed that completely. Thanks for pointing that out.

 

[Gabrell]

If the Variable or any variable mass theory is correct...when atoms are first formed in a particular galaxy, they at first radiate weak, high redshift photons. The redshift would then decrease with time as it evolves.Why do we see redshifts almost everywhere we look? According to variable mass theory, we see redshifts because we see objects as they were when the light left them. If you gaze at a tree 30 feet away, you see the tree as it was 30 nanoseconds ago; if you gaze at a galaxy 10,000,000 light years away, you see it as it was 10,000,000 years ago. Even if the distant matter is the same age as our own, we see the galaxy (or the tree!) as it was when it was younger and less massive--and therefore redshifted.
http://www.ias.ac.in/jarch/jaa/18/435-440.pdf
http://arxiv.org/abs/gr-qc/0212012
Cosmology and the origin of nuclei J.V. Narlikar
Uzbek Journal of Physics
www.ias.ac.in/jaa/junsep2007/JAA521.pdf

 

[Chalnoth]

According to variable mass theory, we see redshifts because we see objects as they were when the light left them.

That's positively ridiculous.