Is dark matter real?

Solomon
Solomon
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RE: RE: Thanks for the

Message 38332 in response to message 38330

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Thanks for the link to Ned's, Odysseus. It's hard to consider one piece of the cosmological puzzle without trying to fit it in with all the rest.

Solomon mentioned:

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There's no reason dark matter should follow the laws of thermodynamics (although, being that it's weakly interacting, one would expect the relaxation time to equilibrium states should be quite long).

Some reasons I considered were principles of invariance and conservation; if these are valid for dark matter, wouldn't thermodynamics necessarily be valid also?

Could dark matter be superfluid helium? Interesting article about how it can act similarly to vacuum, while increasing the moment of inertia of an object, as compared to vacuum. More inertia is like more mass. How would this affect the rotation curve, when scaled up to the size of a galaxy?


I think he meant "There's no reason dark matter should NOT follow the laws of thermodynamics". A double negation is an assertion.
Tullio

Yeah, that.

I guess that's what I get for not proofreading my posts.

Alexander W. Janssen
Alexander W. Janssen
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RE: RE: yeah, i was

Message 38333 in response to message 38331

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yeah, i was pretty pissed after reading this. i really didnt think dark matter was real.

Me too. I always thought it was just regular matter that was not seen, not something entirely different.


Why? I find this rather interesting that they've found something through observation - now thousands of scientists have a safe job and can try to figure out what it really is :-)
Alex.

"I am tired of all this sort of thing called science here... We have spent
millions in that sort of thing for the last few years, and it is time it
should be stopped."
-- Simon Cameron, U.S. Senator, on the Smithsonian Institute, 1901.

Joachim Schmidt
Joachim Schmidt
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RE: Thanks for the link to

Message 38334 in response to message 38329

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Thanks for the link to Ned's, Odysseus. It's hard to consider one piece of the cosmological puzzle without trying to fit it in with all the rest.

Solomon mentioned:

Quote:
There's no reason dark matter should follow the laws of thermodynamics (although, being that it's weakly interacting, one would expect the relaxation time to equilibrium states should be quite long).

Some reasons I considered were principles of invariance and conservation; if these are valid for dark matter, wouldn't thermodynamics necessarily be valid also?

Could dark matter be superfluid helium? Interesting article about how it can act similarly to vacuum, while increasing the moment of inertia of an object, as compared to vacuum. More inertia is like more mass. How would this affect the rotation curve, when scaled up to the size of a galaxy?

No, it can't be superfluid helium, otherwise you could see it ...

Chipper Q
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Thanks, Joachim. If it were

Thanks, Joachim. If it were in the plasma state, or gaseous state, it would surely be visible, as you say. 2 questions: Is there anywhere in the sky that we don't see a spectral signature of helium (is the distribution isotropic)? What about when it's the helium 4 isotope, and behaving as a single boson (ie, in a superfluid state)?

Solomon
Solomon
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RE: Thanks, Joachim. If it

Message 38336 in response to message 38335

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Thanks, Joachim. If it were in the plasma state, or gaseous state, it would surely be visible, as you say. 2 questions: Is there anywhere in the sky that we don't see a spectral signature of helium (is the distribution isotropic)? What about when it's the helium 4 isotope, and behaving as a single boson (ie, in a superfluid state)?

Helium interacts with light. All baryonic matter interacts with light. Dark matter does not. If it did, we would be able to see it and it wouldn't be able to form haloes significantly larger than the local distributions of ordinary matter.

Chipper Q
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RE: RE: Thanks, Joachim.

Message 38337 in response to message 38336

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Thanks, Joachim. If it were in the plasma state, or gaseous state, it would surely be visible, as you say. 2 questions: Is there anywhere in the sky that we don't see a spectral signature of helium (is the distribution isotropic)? What about when it's the helium 4 isotope, and behaving as a single boson (ie, in a superfluid state)?

Helium interacts with light. All baryonic matter interacts with light. Dark matter does not. If it did, we would be able to see it and it wouldn't be able to form haloes significantly larger than the local distributions of ordinary matter.


Since the light used for the observation comes from stars with high concentrations of hydrogen and helium, how can this light be reliably used to show specifically where helium is or isn't, with regard to observations of dark matter regions? Am I to believe that dark matter regions are completely void of normal matter, even hydrogen and helium? What would displace the lightest elements from these regions? Surely not that the galaxy is pulling harder than the dark matter in a gravitational tug-o-war?

Solomon
Solomon
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RE: RE: RE: Thanks,

Message 38338 in response to message 38337

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Thanks, Joachim. If it were in the plasma state, or gaseous state, it would surely be visible, as you say. 2 questions: Is there anywhere in the sky that we don't see a spectral signature of helium (is the distribution isotropic)? What about when it's the helium 4 isotope, and behaving as a single boson (ie, in a superfluid state)?

Helium interacts with light. All baryonic matter interacts with light. Dark matter does not. If it did, we would be able to see it and it wouldn't be able to form haloes significantly larger than the local distributions of ordinary matter.


Since the light used for the observation comes from stars with high concentrations of hydrogen and helium, how can this light be reliably used to show specifically where helium is or isn't, with regard to observations of dark matter regions? Am I to believe that dark matter regions are completely void of normal matter, even hydrogen and helium? What would displace the lightest elements from these regions? Surely not that the galaxy is pulling harder than the dark matter in a gravitational tug-o-war?

If these huge masses of dark matter were just clouds of baryonic matter, they would scatter some of the light from whatever was behind them. We would expect to see unexpected absorption lines when looking at galaxies through the cloud and some amount of emission along lines of sight that don't intersect background objects.

However, to my mind, the more damning part of this is that the ability to interact electromagnetically would give these clouds an easy way to shed energy, which would lead to the size of the clouds decreasing - directly analogous to the way gas clouds can condense to form stars.

The void is, of course, not completely devoid of baryonic matter; but it is there in densities far too low to account for dark matter.

tullio
tullio
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RE: RE: RE: RE: Thank

Message 38339 in response to message 38338

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Thanks, Joachim. If it were in the plasma state, or gaseous state, it would surely be visible, as you say. 2 questions: Is there anywhere in the sky that we don't see a spectral signature of helium (is the distribution isotropic)? What about when it's the helium 4 isotope, and behaving as a single boson (ie, in a superfluid state)?

Helium interacts with light. All baryonic matter interacts with light. Dark matter does not. If it did, we would be able to see it and it wouldn't be able to form haloes significantly larger than the local distributions of ordinary matter.


Since the light used for the observation comes from stars with high concentrations of hydrogen and helium, how can this light be reliably used to show specifically where helium is or isn't, with regard to observations of dark matter regions? Am I to believe that dark matter regions are completely void of normal matter, even hydrogen and helium? What would displace the lightest elements from these regions? Surely not that the galaxy is pulling harder than the dark matter in a gravitational tug-o-war?

If these huge masses of dark matter were just clouds of baryonic matter, they would scatter some of the light from whatever was behind them. We would expect to see unexpected absorption lines when looking at galaxies through the cloud and some amount of emission along lines of sight that don't intersect background objects.

However, to my mind, the more damning part of this is that the ability to interact electromagnetically would give these clouds an easy way to shed energy, which would lead to the size of the clouds decreasing - directly analogous to the way gas clouds can condense to form stars.

The void is, of course, not completely devoid of baryonic matter; but it is there in densities far too low to account for dark matter.


What about axions? See www.cerncourier.com
Tullio

Joachim Schmidt
Joachim Schmidt
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Axions are far too light to

Message 38340 in response to message 38339

Axions are far too light to explain the gravity of dark matter

The dark matter and baryonic matter are mixed in the universe, you too got in touch with dark matter, you just don't recognize this becaus it do only weakly interact with other particles.

The whole gravitational force of a galaxy consists of the various contributions of gravitational force from normal matter like we now it until now, dark matter and vakuum energy ... but thats a different story :=)

greets

Chipper Q
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If dark matter is 'weakly

If dark matter is 'weakly interacting', here's a quote from an abstract concerning the interaction between helium and x-rays:

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X rays in the keV energy regime interact only very weakly with helium atoms. Starting at about 6 keV x-ray energy, the absorption of x rays becomes less important in the ionization of helium than Compton scattering. Whereas for photoabsorption the high-energy asymptotic value for the fraction of helium double ionization is practically reached for keV x rays, the fraction of helium double ionization in Compton scattering is expected to be dependent on the x-ray energy up to much higher energies.


I've read elsewhere that helium (in the 'helium II' state, cooled below ~2.1 K) conducts heat better than any other substance known, as its thermal conductivity is several hundred times that of copper. Maybe a wrong conclusion on my part, but to me this suggests that no scattering is taking place (for helium II).

Seems like it would take the energy of a nova's shockwave to stir it up enough for it to be 'visible'. The reason is that anything less is so weakly interacting and easily conducted. Helium (in the Helium II state) has no boiling point, and the dark matter region is one of tremendous volume and almost no pressure.

I understand what you're saying about emission and absorption, Solomon (and thanks for your patience). From this work on primordial abundance using light from quasars, it looks like there's plenty of hydrogen and helium out there. But it's hard to tell it's there when it isn't ionized.

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