The first thought that comes to my mind, with dark matter proposed at 10^4 K is whether this stuff radiates and what that radiation is. Chad Orzel remarks that its on the order of the temperature of the sun whose radiation we are all familiar with (except those stuck in basement labs). So can we expect a new type of radiation?

Er…because of many different data sets.

Hi Clifford

OK, so people like the Conformal Gravity crowd haven’t analysed the WMAP data yet (there aren’t so many of them, after all) but AFAIK, despite the conventional wisdom, I believe the question is open, no?

I think there are two points to consider here and I am having some confusion with them. I see one that may be appropriate to “warm dark matter” in the form of strangelets? How these are produced and how one might see it in ways that Cliffords sees?

What are the rules here in regards to temperature variation from the cosmic background? Would one find this relation to CFT on the boundary, appropriate as to the conditions, of the blackhole state, applicable, to warm dark matter?

Just one of those nagging itches and how it is related I am not sure Is it okay to think out loud here? Please forgive my ignorance.

Poppycock: I had a bit of a chuckle about the ‘1000 light year bricks’ – I don’t think that’s what’s being suggested at all, although the caveats about it being unpublished apply to my comment as much as anywhere else! That article does rather give the impression of supergalactic structure being based on some kind of invisible Lego. I think it’s a journalistic misunderstanding or unfortunate misphrasing.

Dark matter doesn’t interact electromagnetically, so it won’t radiate electromagnetically. Possibly we don’t know enough to rule out other kinds of radiation, but I am guessing that if it does radiate at all then it isn’t in any currently detectable manner.

On a more general note, it seems that talking about warm and cold dark matter isn’t very helpful. The labels cold, warm and hot dark matter aren’t giving us enough distinction. I’ve already heard this stuff referred to as ‘lukewarm’ and ‘tepid’ in conversation.

Does anyone one hear known the expected temperature of solar axions? It seems this layman that the 10,000 K temperature is consistent with axionic dark matter radiated from the stars in dwarf galaxies.

I believe the article is the handwaving to this Horizon programme on Wed 8th;http://www.bbc.co.uk/sn/tvradio/programmes/horizon/index.shtml

“On next: Most of Our Universe Is Missing
The world’s leading cosmologists seek the Universe’s most elusive secret.”

I have been waiting for this episode, so hopefully I will shed some light (pun intentional!) sometime tomorrow.

I’m sorry I put this post in the wrong thread and mixed up “Clifford’s quote” from that thread and placed it here.:)Yikes!

I’m trying to figure out from the BBC article what exactly has been done here. It looks like they’ve measured the phase-space density in the cores of some dwarf spheroidal galaxies, and then applied Liouville’s theorem to say something about the initial phase space density (and hence the DM temperature).

If this is the case, then one immediate objection is that you only measure the coarse-grained density, which is NOT conserved, but gives a lower bound on the (conserved) fine-grained density.

Also I believe that in simulated DM halos, the regions of high phase-space density are in the subhalos — the central core of a halo generally has pretty low phase-space density. Of course, you don’t probe the subhalos because they have no stars in them. So any estimate of the phase-space density based on the central stellar velocity dispersion is again bound to biased low. I don’t see how they can get anything besides an upper bound on the DM temperature.

Of course, they might have done something entirely different than what I’m guessing, I suppose we’ll have to wait for the paper to come out…

“…then my understanding is that this idea fails, for example, to agree with nucleosynthesis constraints.”

Mannheim in a 1999 paper addresses the original 1993 Knox and Kosowsky issue with nucleosynthesis. Yes, it appears to be a problem, but not necessarily unresolvable.

There’s a conference proceeding from the group on astro-ph today:

http://arxiv.org/abs/astro-ph/0602186

Basically, they are arguing that all of the Milky Way dwarf spheroidals have masses ~ 4 x 10^7 M_sun. The masses come from a straightforward application of the Jeans theorem, with the usual (and perhaps unjustified) assumptions like isotropy. Much of the conclusion is based upon velocity dispersion measurements in the outer parts of the galaxies from small numbers of stars.

What I know on the subject comes from this review on Paul Steinhardt’s webpage.

Shantanu:

Can someone(Sean, Risa, Mark) summarize briefly as to what is the motivation for adding
these exotic properties to cold dark matter particles.

It’s all explained in this paper

I can’t speak for the other models, but inelastic dark matter is for explaining the DAMA/CDMS conflict, not for astrophysics. I don’t think it really effects structure as it’s still pretty non-interacting…