Chandra dark matter announcement could sink MOND

marcus

http://www.nasa.gov/home/hqnews/2006...rk_matter.html

press conference Monday 21 August
CHANDRA team has been watching the highspeed collision of two clusters of galaxies

they can see the GAS of the clusters colliding and getting hot so it radiates Xrays

they may have also seen evidence (lensing) of some of the dark matter passing right through and forming a lobe on the other side

this could be a case where dark matter really acts like a kind of MATTER and not like an effect of modifying gravity as in MOND or relativisitic MOND.

Baez TWF 238 http://math.ucr.edu/home/baez/week238.html discusses this and gives links to previous CHANDRA papers.

Also described at Baez blog
http://golem.ph.utexas.edu/category/...llet_clus.html

here's an abstract:
http://www.cosis.net/abstracts/COSPA...06-A-02655.pdf
Dark matter and the bullet cluster
M. Markevitch (1), S. Randall (1), D. Clowe (2), A. Gonzalez (3), M. Bradac (4) (1) Harvard-Smithsonian Center for Astrophysics, (2) University of Arizona, (3) University of Florida, (4) KIPAC, Stanford University

" 1E0657-56, the "bullet cluster", is a merger with a uniquely simple geometry. From the long Chandra X-ray observation which revealed a classic bow shock in front of a small subcluster, we can derive the velocity of the subcluster and its direction of motion. Recent accurate weak and strong lensing total mass maps clearly show two merging subclusters, including the host of the gas bullet seen in X-rays. This cluster provided the first direct, model-independent proof of the dark matter existence (as opposed to any modified gravity theory) and a direct constraint on the self-interaction cross-section of the dark matter particles. I will review these and other related results."


I think even better is this set of lecture slides from Maxim Markevitch
By a strange coincidence i have been SCUBA diving for several days in the same boat party with Maxim, in the Carribean
these pictures are great the presentation is
2) Maxim Markevitch, Scott Randall, Douglas Clowe, and Anthony H. Gonzalez, Insights on physics of gas and dark matter from cluster mergers
http://cxc.harvard.edu/symposium_200...rgy.html#abs23
you click on the PDF
http://cxc.harvard.edu/symposium_200...itch_maxim.pdf

the pictures show the two clusters colliding, and the very hot ball of gas (ordinary matter)
and then they show the LENSING BACKGROUND mapping the levelcurves of the dark matter density
to show that the dark matter has passed through----and so has been spatially separated from the gas.
so it is not just a mondian gravitational effect OF the gas which would be located around the gas.

if this all checks out it would seem to be an observation of dark matter being a real substance

============
I got help from matt.o editing this post. thx!

Kea

Marcus

There is no incompatibility between extremal black holes and MOND. Only in such supergalactic collisions will stuff start to 'see' the black holes clearly. But effectively, at large scales, the higher genus loopy bits just contribute to gravity, so one needs to take into account the modifications to GR coming from the scalar and vector components.

Of course, I might be wrong.

john baez

Yes - shooting from the hip, I feel that MOND is dead.

Mike2

I'm not sure this proves that dark matter is an exotic form of permanent matter. If dark matter were some sort of zero point energy effect that surrounds heavy objects, wouldn't this effect have its own momentum and overshoot the matter it is normally stuck to if that matter is stopped somehow? I suspect such an overshoot would dissipate differently from permanent matter. Permanent matter would have to orbit back around and rejoin the collective. An overshoot of zero point energy would probably just dissipate in all directions.

Afterall, the vacuum energy (zero point energy) is not zero, right? Therefore is has a mass density. Therefore it is attracted to matter, right? So I suppose dark matter may be the weight of the vacuum energy being concentrated around matter. As more vacuum energy is gathered around, then more of it is attracted to the additional weight. Iterating this process forever might account for all that extra mass around galaxies.

matt.o

Mike2, the point is that the baryonic mass in clusters is dominated by the intracluster medium (ICM) by about 4:1. In the bullet cluster, we see a significant offset between the mass contours derived form the weak lensing analysis and the position of the ICM. The position of the two mass centroid aligns with that of the cluster an infalling subcluster. If there were no dark matter, we would expect the mass countours to coincide with the ICM, where the dominant baryonic mass component is.

I suspect the MONDians will carry on, but I think this is quite a heavy blow, especially if we can find a sample of clusters merging in the plane of the sky and undertake similar analyses.

matt.o

Wow John, that optical image of the bullet is spectacular! I'm a bit biased when it comes to clusters, but pictures like that just get my heart pumping!

Mike2

If vacuum energy accumulation is iterative, i.e. if more of it is attracted to previous accumulations of it, then is this an alternate description of propagation or momentum, where the next value depends on the previous value? If so, then vacuum energy can overshoot the matter is normally surrounds and propogate like waves.

If vacuum energy accumulates (whether it is dark matter or not), then I suppose that the gravitational effects of this additional accumulation would only be noticeable around low density objects more comparible to the vacuum energy density, such as galaxies. High density objects such as stars and planets would create too much of a contrast to make this additional vacuum energy accumulation noticeable.

So far this sounds like a qualitative argument for all the effects of dark matter. I don't have the time or even the math skills to prove any of this. So if anyone else would like to persue the "matter", be my guess. Thank you.

Continuing with this...
If the vacuum energy can be higher or lower, accumulate and disperse, then could the universe expand to the point of making the vacuum energy so comparatively high that it is unstable and falls to a lower vacuum energy - perhaps forcing matter out of it in the process like some sort of Higgs mechanism. Food for thought. Have fun with it.

marcus

did anybody else hear a deplorable pun ricochet off the canyon wall?

marcus

http://www.nasa.gov/home/hqnews/2006...rk_Matter.html

press release based on today's press conference
MOND is dead, as expected

===quote===

NASA Finds Direct Proof of Dark Matter

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.

"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."

In galaxy clusters, the normal matter, like the atoms that make up the stars, planets, and everything on Earth, is primarily in the form of hot gas and stars. The mass of the hot gas between the galaxies is far greater than the mass of the stars in all of the galaxies. This normal matter is bound in the cluster by the gravity of an even greater mass of dark matter. Without dark matter, which is invisible and can only be detected through its gravity, the fast-moving galaxies and the hot gas would quickly fly apart.

The team was granted more than 100 hours on the Chandra telescope to observe the galaxy cluster 1E0657-56. The cluster is also known as the bullet cluster, because it contains a spectacular bullet-shaped cloud of hundred-million-degree gas. The X-ray image shows the bullet shape is due to a wind produced by the high-speed collision of a smaller cluster with a larger one.

In addition to the Chandra observation, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes were used to determine the location of the mass in the clusters. This was done by measuring the effect of gravitational lensing, where gravity from the clusters distorts light from background galaxies as predicted by Einstein's theory of general relativity.

The hot gas in this collision was slowed by a drag force, similar to air resistance. In contrast, the dark matter was not slowed by the impact, because it does not interact directly with itself or the gas except through gravity. This produced the separation of the dark and normal matter seen in the data. If hot gas was the most massive component in the clusters, as proposed by alternative gravity theories, such a separation would not have been seen. Instead, dark matter is required.

"This is the type of result that future theories will have to take into account," said Sean Carroll, a cosmologist at the University of Chicago, who was not involved with the study. "As we move forward to understand the true nature of dark matter, this new result will be impossible to ignore."

This result also gives scientists more confidence that the Newtonian gravity familiar on Earth and in the solar system also works on the huge scales of galaxy clusters.

"We've closed this loophole about gravity, and we've come closer than ever to seeing this invisible matter," Clowe said.

These results are being published in an upcoming issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center, Cambridge, Mass. For additional information and images, visit:

http://chandra.nasa.gov
===endquote===

neutrino

Completely forgot about this. Thanks for the update, marcus.

EL

This bullet cluster phenomena was published like half a year ago. Why do NASA go out with this now? Is it because they wanted it to be confirmed by longer observation time, or what is really the new stuff this time?

marcus

EL, I will tell you that my interest in this is very much from a Quantum Gravity viewpoint.
It is a matter of real interest if QG theories should duplicate Gen Rel at large scale (in the "classical limit") or whether, like, the evolution rules by which spin networks evolve should imitate some OTHER modified version like Bekenstein TeVeS.

So I see this issue to be really crucial for non-string QG theorists.

So I totally want them to be REALLY SURE about this, when they shoot down TeVeS MOND.

==================
now, assuming the stake is driven thru TeVeS heart, it becomes very exciting to think about Smolin MATTER TANGLES in connection with dark matter.

because for instance just as a wild speculative possibility to consider: the dark matter halo could be a kind of effervescing "noise" of LITTLE TANGLES in the spinnetwork.

You know the theory they worked out last year with Bilson-Thompson where many of the ordinary Standard particles are definite knots or braids which are STABLE in the spinnetwork. new scientist just had an article about that by Castelvecchi.
Check Bilson-Thompson on arxiv, if you want to read more.

Well it is possible, I think, for a spinnetwork to have pseudotangles that are in between no-tangle and a permanent stable tangle----it could be a noise that unavoidably surrounds ordinary stable matter and which has some matter-like properties.

anyway maybe that is a viable idea and maybe not, the overarching issue is that the language of spinnetworks has been seen able to express matter---to express other stuff besides the quantum states of geometry (which rovelli-smolin used it for). If it can express other stuff besides quantum states of geometry, and IF there is no MOND but instead something with momentum able to non-interact with ordinary tangles, then one can safely try to look for ways to express that in spinnetwork language. So that makes it exciting from a QG viewpoint.

You see why I would be glad for it to be as certain as possible that MOND is dead as possible

Have to say I'm glad they gave the Clowe team that extra 100 hours of Xray telescope time on CHANDRA.

EL

Yeah sure, I think it was good too. However I got the impression NASA was going to present some completely new stuff, but they really just confirmed what was already "known", hence my dissapointment.
Anyway, we all know since long ago that the dark matter is the LSP, don't we?

marcus

Lightest Supersymmetric Particle?

Leftover Spinach?

Louisiana State Police

turbo

It's quite interesting that when trying to ID dark matter, astronomers look for really exotic hard-to-detect forms of matter, while ignoring the real hard-to-detect matter (virtual particles) that quantum theorists assure us populate the vacuum. If the vacuum contains the bulk of the mass-energy in the universe (it runs to infinity if we do not assume a UV cutoff) why cannot it have gravitational consequences for the "real" world? It's a puzzle why this is not being seriously considered in mainstream cosmology.

EL

What a chock if some of those materialized at LHC!

kneemo

In the interview with Maxim Markevitch it sure does sound that way.

See Astrophysicist Maxim Markevitch on Dark Matter, where he states:

"Furthermore, some observations are difficult to explain with the current DM models. This is why people also explored alternatives to DM, for example, modifying the gravity laws on intergalactic scales in such a way that visible matter would be sufficient to explain all those effects that we normally ascribe to DM. This idea has now been disproved -- although we did not prove that gravity laws are correct, we did show unambiguously that there is dark matter on cluster scales, not just the visible matter."