NASA Finds Direct Proof of Dark Matter, Chandra returns findings Options

[lyford]

Chandra Press Release

Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.

"This is the most energetic cosmic event, besides the Big Bang, which we know about," said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

These observations provide the strongest evidence yet that most of the matter in the universe is dark. Despite considerable evidence for dark matter, some scientists have proposed alternative theories for gravity where it is stronger on intergalactic scales than predicted by Newton and Einstein, removing the need for dark matter. However, such theories cannot explain the observed effects of this collision.

Apologies if this is a repost

[nprev]

Okay...so, the question remains, just what the heck IS dark matter??? Fat neutrinos (well...they're leptons, but still...)? Virtual particle flux (or is that dark energy?) Higgs bosons? I'm so confused!!!

[Rob Pinnegar]

I'm so confused!!!

So is everybody else.

I don't claim to know much about the dark matter conundrum, but it doesn't seem like the sort of thing that is going to be resolved any time soon. (There'll be a nice juicy Nobel Prize waiting for whoever does resolve it, though.)

[chris]

There is a very nice explanation of this paper here.

Chris

[lyford]

All right you WIMPs, here is a link to the actual paper -

A DIRECT EMPIRICAL PROOF OF THE EXISTENCE OF DARK MATTER ? (PDF)

That was a great article, thanks chris

[tty]

Okay...so, the question remains, just what the heck IS dark matter??? Fat neutrinos (well...they're leptons, but still...)? Virtual particle flux (or is that dark energy?) Higgs bosons? I'm so confused!!!

Poul Anderson once wrote a story based on the premise that there was two types of matter in the universe. These were essentially identical except that each kind only interacted strongly and electromagnetically with itself but weakly and gravitationally also with each other. The result would be two essentially similar and co-existing universa each invisible and not easily detectable to the other. I suppose the cross-universe weak interaction was necessary for the story line which included contact with a civilisation in the "other" universe (try to communicate by gravity waves!).

I don't suppose it is a very likely scheme, but it's a fascinating idea.

tty

[Mongo]

I would not be so quick to dismiss MOND-like theories. HERE is a link to a preprint that demonstrates that the observed effects around the 'bullet' galaxy are in fact what is expected from a MOND theory, provided that the neutrino has a mass of about 2 eV -- which mass is also expected under MOND by observations of dense galaxy clusters.

As usual, the advocates of CDM loudly proclaim that MOND is dead, due to some new observation, when in fact that observation is just as explainable using a MOND-like theory. This has happened repeatedly in the past several years.

I should point out that I favour a MOND-like theory, because it is much more elegant than any CDM theory that matches observations. The currently popular CDM theories increasingly remind me of Ptolemy's epicycles, in their ever-more-elaborate modifications, needed to match new observations -- whereas MOND-like theories have required substantially fewer ad hoc changes. The only real modification needed for MOND to match observation since it was first proposed is the 2 eV neutrino (which also fits within standard physics) -- compared to the far more numerous, and more removed from standard physics, modifications to the CDM theories required in the same time span.

Bill

[ljk4-1]

Poul Anderson once wrote a story based on the premise that there was two types of matter in the universe. These were essentially identical except that each kind only interacted strongly and electromagnetically with itself but weakly and gravitationally also with each other. The result would be two essentially similar and co-existing universa each invisible and not easily detectable to the other. I suppose the cross-universe weak interaction was necessary for the story line which included contact with a civilisation in the "other" universe (try to communicate by gravity waves!).

I don't suppose it is a very likely scheme, but it's a fascinating idea.

tty

Wild (but Fun) Speculation Time:

If the brane model of the Universe(s) is correct, perhaps LISA will be picking up
something else when she detects those distant gravity waves from colliding black
holes.

http://www.phys.lsu.edu/mog/mog25/node7.html

[The Messenger]

Okay...so, the question remains, just what the heck IS dark matter??? Fat neutrinos (well...they're leptons, but still...)? Virtual particle flux (or is that dark energy?) Higgs bosons? I'm so confused!!!

Dark matter remains the difference between what Newtonian gravity predicts, and what we observe.

This single observation does not kill other candidate phenologies, as the authors suggest. This is clearly a collisional event, and we are a long ways from understanding all of the kinematics of galaxy-galaxy collisions. It is not possible to eliminate 'conventional' dark matter - such as cool dust and/or neutrinos in this event that is not akin to the many, many cases where MOND phrenology correctly predicts the outcome.

[tfisher]

A response from the MOND camp is in the following preprint:
http://arxiv.org/PS_cache/astro-ph/pdf/0609/0609125.pdf
Basically, they say that the gravitational lensing data that was presented as proof that there must be dark matter and which couldn't be explained by the modified Newtonian gravity theory was too strong a claim. The data still seems to be consistent with MOND, up to having neutrino mass be very large within the current experimental constraints. So the debate continues...

[Mongo]

A response from the MOND camp is in the following preprint:
http://arxiv.org/PS_cache/astro-ph/pdf/0609/0609125.pdf

I had posted a link to that paper already, in post #7 of this thread.

Bill

[ljk4-1]

Is dark matter just so much very fine dust?

http://arxiv.org/abs/astro-ph/0609500