MadSci Network: Astronomy

Re: Does Dark Matter Possess Vibrational Energy?

Date: Thu Jul 24 14:48:53 2003
Posted By: Todd Whitcombe, Associate Professor, Chemistry
Area of science: Astronomy
ID: 1058827412.As

That is one loaded question! How to answer? I suppose that it would 
depend upon what you mean (and the scientists in the article mean) by 
both "dark matter" and "vibrational energy".

So, let's begin with a little cosmology. NASA's Wilkinson Microwave 
Anisotropy Probe has mapped out the microwave background of the visible 
Universe. The results of this detailed map tell us that the Universe 
consists of 4% matter, 23% dark matter, and 73% dark energy. This means 
that everything that we can see - all of the atoms in all of the stars 
throughout the Universe - amounts to only 4% of the 27% of the Universe 
that is "normal" matter. I put normal in quotes because it may or may not 
be the baryonic matter that is around us.

But if it is, then dark matter is just the stuff of the Universe that 
isn't shining. And there are a lot of candidates - such as Massive 
Compact Halo Objects (MACHOs). These are things like the remnants of 
stars or red dwarfs or large planets and since they consist of ordinary 
matter under ordinary conditions, the presumption would be that they 
would behave in a manner consistent with the laws of physics as we know 
them. Hence, they should possess "vibrational energy" - if by that, we 
mean energy associated with vibrational states. That is, they are not at 
absolute zero. Indeed, many of these objects - such as red dwarf - would 
have considerable vibrational energy as they are still "stars" and are 
emitting radiation, albeit very weakly.

I could also add black holes to the list of MACHOs but I am not sure how 
I would classify black holes in terms of matter. Clearly, they have mass 
and are generated from stellar material - from baryons. But as a 
singularity, they have no dimensions and are not akin to other forms of 
matter. That aside, the question of whether or not they have vibrational 
energy is perplexing. Yes, they do radiate. And if by "vibrational 
energy" we mean temperature, then yes, they do have temperature (or, at 
least, there is a temperature that we can ascribe them). But if 
by "vibrational energy", you mean non-zero point vibrational modes, I 
doubt that they do. A black hole doesn't radiate in the infrared region 
of the spectrum (or, at least, no one has detected a black hole radiating 
in the infrared...) and it is difficult to see how they could. On the 
other hand, since the event horizon prevents us from peering in (or 
radiation from coming out), I am not sure that a black doesn't.

So, if dark matter is "normal" matter that is simply not radiant, then it 
is likely to have vibrational energy. On the other hand, if has 
vibrational modes, they the lower energy end of the electromagnetic 
spectrum should be obscured. That is, the dark matter throughout the 
Universe should be absorbing low wavelength radiation and re-emitting it 
at even lower wavelengths. Since the new emission spectrum would be quite 
different from the absorption spectrum, this should be a way to look for 
dark matter. But this absorption/emission has yet to be observed. So, the 
dark matter may be either concentrated in MACHOs or a particle that is 
completely invisible to the electromagnetic spectrum in which case it 
would be hard to argue that it has "vibrational energy". That is, it a 
particle is non-interacting with electromagnetic radiation, then it can't 
very well be absorbing or emitting radiation. No absorption or emission - 
no temperature, no vibrations.

I should point out that the Hubble space telescope has been used to 
explore the question of dark matter on many occasions. In one set of 
results, the astronomers did not "see" dark matter but rather they were 
able to map the consequences of dark matter and in so doing, demonstrate 
that it pervades a galactic cluster. That is, they were able to see the 
gravitational effects of dark matter without actually observing the dark 
matter itself. In another report, a distant red dwarf was observed after 
it had resulted in the gravitational lensing of light from a distant 
star. The position of the dwarf mark it as a MACHO and provides evidence 
for at least some of the dark matter in our galaxy to be made out of 
massive "normal" objects.

But I guess the final answer to your question is, we don't really know 
what makes up the 23% of the Universe that is "dark matter" and until we 
do, we can't know what are its properties. Great question, though!

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