Chandra dark matter announcement could sink MOND

[marcus]

http://www.nasa.gov/home/hqnews/2006/aug/HQ_M06128_dark_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/2006/08/dark_matter_in_the_bullet_clus.html

here's an abstract:
http://www.cosis.net/abstracts/COSPAR2006/02655/COSPAR2006-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_2005/proceedings/theme_energy.html#abs23
you click on the PDF
http://cxc.harvard.edu/symposium_2005/proceedings/files/markevitch_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]

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

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]

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

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]

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.

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 pursue 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]

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

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

 

[marcus]

http://www.nasa.gov/home/hqnews/2006/aug/HQ_06297_CHANDRA_Dark_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]

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?

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]

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.

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]

...
Anyway, we all know since long ago that the dark matter is the LSP, don't we?

Lightest Supersymmetric Particle?

Leftover Spinach?

Louisiana State Police

 

[turbo]

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.

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]

Louisiana State Police

What a chock if some of those materialized at LHC!

 

[kneemo]

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

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

See http://chandra.harvard.edu/photo/2006/1e0657/qa.html" , 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."

 

[marcus]

Hi Kneemo, congratulations on your new blog

Sean Carroll has a really GREAT report on the whole thing over at CV.
thanks to neutrino for flagging it!
it has this animation of the collision

http://chandra.harvard.edu/photo/2006/1e0657/media/bullet.mpg

Here is the CV report by Sean
http://cosmicvariance.com/2006/08/21/dark-matter-exists/

Here is the master page at chandra site
http://chandra.harvard.edu/photo/2006/1e0657/media/

it has several animations and a lot of stills and links to other stuff
also photos of Maxim, Doug and SeanTheir journal article
A DIRECT EMPIRICAL PROOF OF THE EXISTENCE OF DARK MATTER
will appear on the arxiv in a couple of hours (Monday 8PM eastern) as
http://arxiv.org/abs/astro-ph/0608407

and we can get advance copies (pre-arxiv) at that main page
http://chandra.harvard.edu/photo/2006/1e0657/media/paper.pdf

 

[Mike2]

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.

I agree that it should be studied for its own sake, whether it is dark matter or not. Perhaps the reason that the vacuum energy is not yet considered is that it may not be understood what would vary in the zero point energy calculations that would produce a differring overall energy density. Wait, wouldn't that be the coupling constant for matter, and isn't this the same as the cosmological constant? I thought I read that somewhere long ago.

If so, then at the risk of being bumped into the "Theory Development" forum, let me throw out a suggesting on how a calculation might proceed to determine whether an accumulation of vacuum energy might be dark matter, at least as an order of magnitude calculation.

I suppose that a differential volume of space would have an energy density and thus a mass density that would be attracted to matter until that force is balanced by the a force in the opposite direction produced by the changing energy density of the vacuum energy itself. This differential equation would produce an equation of energy density as a function of distance to the bulk of the mass. That energy density can be integrated and produce the additional equivalent mass around the bulk. That additional mass density may attract even more vacuum energy so that the process may need to be iterated to convergence. That final accumulation of additional mass may well be equal to the dark matter.

 

[Chronos]

For further discussion see:

A direct empirical proof of the existence of dark matter
http://arxiv.org/abs/astro-ph/0608407

Authors: Douglas Clowe (1), Marusa Bradac (2), Anthony H. Gonzalez (3), Maxim Markevitch (4), Scott W. Randall (4), Christine Jones (4), Dennis Zaritsky (1) ((1) Steward Observatory, Tucson, (2) KIPAC, Stanford, (3) Department of Astronomy, Gainesville, (4) CfA, Cambridge)
Comments: Accepted for publication in ApJL

"We present new weak lensing observations of 1E0657-558 (z=0.296), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-ray emitting plasma are spatially segregated. By using both wide-field ground based images and HST/ACS images of the cluster cores, we create gravitational lensing maps which show that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. An 8-sigma significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen."

I second the motion by John Baez - this is a stake in the heart of MOND. I admit I was already convinced the beast had been slain by other evidence, but, this is the most compelling to date.

 

[Mike2]

I second the motion by John Baez - this is a stake in the heart of MOND. I admit I was already convinced the beast had been slain by other evidence, but, this is the most compelling to date.

I'm not so sure. If gravity is modified and stronger on galatic scales, then perhaps this offset of lensing/gravitational effect, or this overshoot in the gravitational field, is just another form of a gravitational wave. Similar to an electric field around a proton when the proton is suddenly stopped and the electric field continues to travel on its own for a bit before re-centering around the proton, the stronger gravitational field around a galaxy may travel a bit on its own and overshoot the galaxy before re-centering around the galaxy again. The question is how fast these gravity fields travel on galatic scales. If we knew more about the dynamics of these galaxies we could be more sure. So the fact that the gravitational field may be offset from a suddenly stopped galaxy does not prove that MOND is wrong. The gravitational field may simply have a momentum of its own. Feel free to shoot this theory down if you'd like.

 

[Dcase]

Two questions

1 - How is the dark matter subject of this thread different from detectable, but essentially invisible neutrinos passing through planets like Earth?

2 - How does the visible gas collision differ from Cherenkov radiation?

 

[turbo]

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.

marcus, have you reviewed this recent paper by Padmanabhan? http://arxiv.org/PS_cache/gr-qc/pdf/0606/0606061.pdf
In it, he proposes modeling the vacuum as an elastic solid (similar to Sakharov). I fear that he is making a mistake in claiming that changes in the vacuum's properties can have no gravitational consequence, though. If the vacuum has a critical role in gravitation, it must be dynamical, not static. The vacuum is not a painted background against which the play (of gravitation) is presented, it is a star in the play.

 

[marcus]

... have you reviewed this recent paper by Padmanabhan? http://arxiv.org/PS_cache/gr-qc/pdf/0606/0606061.pdf
In it, he proposes modeling the vacuum as an elastic solid (similar to Sakharov)...

hi turbo, we might need a separate thread for this. I don't immmediately see the connection to dark matter (or the late MOND). But perhaps you can explain or someone else will see the connection.
Provisionally, I will paste in the abstract so we can see what you are talking about:

http://arxiv.org/abs/gr-qc/0606061
Gravity: A New Holographic Perspective
T. Padmanabhan
Plenary talk at the International Conference on Einstein's Legacy in the New Millennium, December 15 - 22, 2005, Puri, India; to appear in the Proceedings to be published in IJMPD; 16 pages

"A general paradigm for describing classical (and semiclassical) gravity is presented. This approach brings to the centre-stage a holographic relationship between the bulk and surface terms in a general class of action functionals and provides a deeper insight into several aspects of classical gravity which have no explanation in the conventional approach. After highlighting a series of unresolved issues in the conventional approach to gravity, I show that (i) principle of equivalence, (ii) general covariance and (iii)a reasonable condition on the variation of the action functional, suggest a generic Lagrangian for semiclassical gravity of the form $L=Q_a^{bcd}R^a_{bcd}$ with $\nabla_b Q_a^{bcd}=0$. The expansion of $Q_a^{bcd}$ in terms of the derivatives of the metric tensor determines the structure of the theory uniquely. The zeroth order term gives the Einstein-Hilbert action and the first order correction is given by the Gauss-Bonnet action. Any such Lagrangian can be decomposed into a surface and bulk terms which are related holographically. The equations of motion can be obtained purely from a surface term in the gravity sector. Hence the field equations are invariant under the transformation $T_{ab} \to T_{ab} + \lambda g_{ab}$ and gravity does not respond to the changes in the bulk vacuum energy density. The cosmological constant arises as an integration constant in this approach. The implications are discussed."

turbo, this could have some bearing on the notion of *dark energy*, but I don't see how it involves *dark matter*, am I missing something?

 

[turbo]

hi turbo, we might need a separate thread for this. I don't immmediately see the connection to dark matter (or the late MOND). But perhaps you can explain or someone else will see the connection.
Provisionally, I will paste in the abstract so we can see what you are talking about:

http://arxiv.org/abs/gr-qc/0606061
Gravity: A New Holographic Perspective
T. Padmanabhan
Plenary talk at the International Conference on Einstein's Legacy in the New Millennium, December 15 - 22, 2005, Puri, India; to appear in the Proceedings to be published in IJMPD; 16 pages

"A general paradigm for describing classical (and semiclassical) gravity is presented. This approach brings to the centre-stage a holographic relationship between the bulk and surface terms in a general class of action functionals and provides a deeper insight into several aspects of classical gravity which have no explanation in the conventional approach. After highlighting a series of unresolved issues in the conventional approach to gravity, I show that (i) principle of equivalence, (ii) general covariance and (iii)a reasonable condition on the variation of the action functional, suggest a generic Lagrangian for semiclassical gravity of the form $L=Q_a^{bcd}R^a_{bcd}$ with $\nabla_b Q_a^{bcd}=0$. The expansion of $Q_a^{bcd}$ in terms of the derivatives of the metric tensor determines the structure of the theory uniquely. The zeroth order term gives the Einstein-Hilbert action and the first order correction is given by the Gauss-Bonnet action. Any such Lagrangian can be decomposed into a surface and bulk terms which are related holographically. The equations of motion can be obtained purely from a surface term in the gravity sector. Hence the field equations are invariant under the transformation $T_{ab} \to T_{ab} + \lambda g_{ab}$ and gravity does not respond to the changes in the bulk vacuum energy density. The cosmological constant arises as an integration constant in this approach. The implications are discussed."

turbo, this could have some bearing on the notion of *dark energy*, but I don't see how it involves *dark matter*, am I missing something?

Read sections 1.5 and 3.0 particularly, where he states that the bulk vacuum energy density cannot manifest itself with a real-world gravitational effect. He has made a leap that I did not expect within my lifetime (except in my own cosmological model), but has qualified it in such a way as to gut it. At some point, cosmologists and quantum theorists have to sit down and talk. QT folks have to learn that locality is important on the quantum scale, and GR folks have to learn that QT concepts have real-world consequences.

 

[ccdantas]

Very interesting thread on Padmanabhan's article; I suggest you post it separately.

Concerning the new results on dark matter from the analysis on the Bullet cluster, I thought you may find this interesting (sorry it it has already been discussed):

Can MOND take a bullet? Analytical comparisons of three versions of MOND beyond spherical symmetry, by Garry W. Angus, Benoit Famaey, HongSheng Zhao [astro-ph/0606216]

I've made some general considerations over at my blog; I'll reproduce them here in case someone finds them interesting:


------
Some overall consistency checks on this phenomenon should be performed:

1) The two clusters would show up as outliers from the “fundamental plane” relation of clusters in the space of 2-component (baryonic+DM) virial theorem parameters [Dantas et al. ApJ Letters, 528, L5, 2000, astro-ph/9910541];

2) N-body gravitational simulations of merging of 3-component cluster models (galaxies+DM+ gas) with appropriate masses and orbital configurations should be performed in order to check the overall consistency of the observed dynamical timescales.

3) It would be still valuable to perform similar N-body simulations with gravity law modified to include MOND terms, that is: mixed simulations with DM and MOND in order to verify whether the phenomenon can still be reproduced under (some level of) MOND.

I also have some old calculations on DM cross sections available to download from my blog.

Thanks,
Christine

 

[selfAdjoint]

hi turbo, we might need a separate thread for this

Marcus, you already made one" https://www.physicsforums.com/showthread.php?t=124959&highlight=padmanabhan

 

[marcus]

Marcus, you already made one" https://www.physicsforums.com/showthread.php?t=124959&highlight=padmanabhan

right! thanks for reminder and link. Turbo, what would you say to posting further comment on that earlier Padmanabhan link?
I may be missing your point, but I don't see how it fits in here which is mainly about that evidence contrary to MOND

 

[ohwilleke]

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

See http://chandra.harvard.edu/photo/2006/1e0657/qa.html" , 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."

Markevitch is actually quite cagey in that quote. He leaves open the idea that DM might be specific to cluster level phenomena and that subcluster level phenomena might be MONDish. Given that almost all the contra-MOND evidence is at the cluster level, there is something to be said for that caution.

I think the that DM only in clusters theory is a lot less attractive than a no DM theory, and we sure seem to have some DM (although this http://arxiv.org/PS_cache/astro-ph/pdf/0606/0606216.pdf" (PDF) does begin the process of a more careful analysis).

The "Direct Proof" article which doesn't do as serious an analysis as is really called for to really disprove MOND -- mostly because the "Direct Proof" article uses straight GR to produce its DM map, and then uses the difference between the DM map and the visible matter distribution to show that straight GR plus DM is the only possible solution. In effect, he assumes a non-MOND theory and then uses a chain of reasoning that relies on that assumption to show that gravity is non-MOND.

Now, that doesn't mean that he's wrong. A spatial disparity between the apparent source of gravity lensing effects and visible matter distributions had previously been identified in other articles as a valid way to falsify modified gravity theories generally. But, since many MOND elaborations behave most differently from each other and GR in multiple body contexts, and because this is a classic multi-body situation, and because few people have worked out the predicted physics in this kind of multi-body situation, simply saying it is disproven, rather than that it now looks much more likely that it will not be able to address the situation, would be more accurate.

 

[turbo]

right! thanks for reminder and link. Turbo, what would you say to posting further comment on that earlier Padmanabhan link?
I may be missing your point, but I don't see how it fits in here which is mainly about that evidence contrary to MOND

OK, the point is that the function of DM could be played by the vacuum. Where I think that Padmanabhan is missing the point is that in his recent paper, he denies the vacuum a dynamical nature, and a dynamical nature is exactly what the vacuum needs if it is to supply the extra gravitational attraction seen in galaxies and in clusters. The vacuum needs to be able to exhibit polarization in the presence of matter in order to provide a stronger gravitational attraction than predicted by GR. Einstein was looking for such a dynamical, local entity when he assured people that GR needed an "ether". (See the signature.)

MOND is an ad-hoc modification of gravity that seems to work well in some classes of galaxies, but it does not have unlimited applicability. It is no more illustrative of the mechanics of gravitation than is GR. This is why Padmanabhan's extension of Sakharov's hypothesis is an important step. It is a recognition of the need for a mechanism for gravitation - the next step is to demand that the interaction be dynamic, and to understand that the polarization of the vacuum does not occur at the speed of light. If the refraction of light through a cluster is dependent on the density of the vacuum in that region, the observation of "dark matter" in the NASA announcement is nothing more than the observation of gradients in vacuum density. We do not need exotic particles to provide the effects of DM - quantum theorists will tell us that the vacuum is a very busy place and contains the bulk of the mass-energy of our Universe, although it is only weakly interactive with condensed matter. LQG folks are poking around at the margins of this concept, by treating space as if it has fine structure. Again, the trick is that the scale of the fine structure of a given space should be variable, based on the quantity and location of embedded matter, or we end up with a limited kinetic model of gravity instead of a dynamical one.

 

[Mike2]

Do we have the capability to determine the exact distribution of the matter necessary to give us the lensing effect in the dark matter region? An exact distribution of dark matter would probably distinguish between any kind of permanent matter which would continue to clump together and a vacuum energy effect which would tend to dissipate once free of the matter that formed it. I suspect computer simulations might show us that this distribution could not come from a form of matter that's gravitationally attracted to itself.

 

[ohwilleke]

Exact is a very demanding word. Resolution gets better and better, but it is never perfect, and is inherently limited by the number of lensed objects between Earth and the cluster whose lensing can be observed.

 

[SpaceTiger]

Markevitch is actually quite cagey in that quote. He leaves open the idea that DM might be specific to cluster level phenomena and that subcluster level phenomena might be MONDish. Given that almost all the contra-MOND evidence is at the cluster level, there is something to be said for that caution.

I suspect that wasn't his reason for being cagey. If there is dark matter on cluster scales, it would be very strange if there were no dark matter on galaxy scales as well. The caveat about modified gravity is most likely there to allow for large-scale, strong-field, or quantum modifications to GR.

 

[asciencebuff]

I suspect that wasn't his reason for being cagey. If there is dark matter on cluster scales, it would be very strange if there were no dark matter on galaxy scales as well. The caveat about modified gravity is most likely there to allow for large-scale, strong-field, or quantum modifications to GR.

can someone tell me (I'm 16 ) if this paper supports or contradicts MOND (it says it contradicts relativity but not a word on MOND!) ? http://arxiv.org/abs/physics/0608026" I am going to use it i n my science project on DARK MATTER DISCOVERY . this guy (or a lady) computes gravity on different scales like you guys say is possible after this historic NASA discovery. I would also need more papers like this-- what are my Google keywords here ?
I know Einstein proved Newton wrong long time ago but does this all mean that MOND is incorrect even though it doesn't say so? or is MOND no longer questioned?

also is it OK (ethical)to use geologic papers to disprove physics trheory like relativity (or MOND)? would my prof get mad if I used this paper ? THANKS!

 

[selfAdjoint]

can someone tell me (I'm 16 ) if this paper supports or contradicts MOND (it says it contradicts relativity but not a word on MOND!) ? http://arxiv.org/abs/physics/0608026" I am going to use it i n my science project on DARK MATTER DISCOVERY . this guy (or a lady) computes gravity on different scales like you guys say is possible after this historic NASA discovery. I would also need more papers like this-- what are my Google keywords here ?
I know Einstein proved Newton wrong long time ago but does this all mean that MOND is incorrect even though it doesn't say so? or is MOND no longer questioned?

also is it OK (ethical)to use geologic papers to disprove physics trheory like relativity (or MOND)? would my prof get mad if I used this paper ? THANKS!

{Added in edit} After wscanning it, I believe the paper you are citing is unsound. It is not absolutely unheard of that a local phenomenon like resonance could be extended over many orders of magnitude, but it is something that has to be shown in detail, not just by plugging numbers into an equation. Please find something else for your project.
The new observations are very strong evidence against MOND but not absolutely conclusive. The MOND partisans are trying to work around the physicality of dark matter. There are two papers containing the observations and their interpretation. What I'm sure your prof wants is not a blind acceptance of the new interpretations but a critical attitude showing independence of mind and ability to tell a hawk from a handsaw. (extra brownie points for spotting where the quote comes from).

MOND was never intnded as a serious contender for explaining the universe, rather it was in the spirit of "See if we can modify gravity a little to make these things (galaxy turning ratios) happen instead of positing matter that no-one can see".

Although as you say, GR reduces Newtonian gravity to a special case, yet that special case ("flat" spacetime) is a good approximation of how spacetime is on the scale of a galaxy. Individual stars have their gravity wells but the overall geometry, as analysis of the microwave background has suggested, is analogous to a flat plain with a lot of little pits scattered about it. The pits don't change the fact that overall, the landscape is flat. And in a flat spacetime, Newtonian gravity is an adequate approximation. So it was Newtonian gravity that they modified to make MOND.

I believe Marcus has a thread devoted to MOND papers, do a "search this forum" on MOND.