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trinitree88
2016-Sep-21, 03:18 PM
The authors propose a correlation between the acceleration due to baryons and the acceleration observed in 153 rotationally supported galaxies of different morphologies. SEE:https://arxiv.org/abs/1609.05917

George
2016-Sep-22, 04:12 PM
That is interesting enough to ask if you would convert it into georeeze? The claim for a fairly constant baryonic mass/light ratio (psi) looks cool. I'm a little confused, due to rushing things these days, on what they are saying about the flat rotation profiles. What is here that would stir Vera Rubin?

kzb
2016-Sep-23, 12:45 PM
Actually Stacy McGaugh has been writing similar papers for a long time.

Even the fine details of a galactic rotation curve fits to the distribution of baryons. The shape of the rotation curve is governed entirely by the baryon distribution. it's a powerful argument against the non-baryonic halo matter models of galaxies.

Thanks for highlighting this paper I will try and read it later.

borman
2016-Sep-23, 10:30 PM
A Milgrom comment

In response to McGaugh et al paper, Milgtom has put out a short paper finding that the MOND hypothesis predicted this support.

http://arxiv.org/abs/1609.06642v1

McGaugh et al did mention MOND in the conclusion but was trying to keep distance or separation between theory and observation. While the correlation between baryons and rotation seems promising at these 153 galaxy samples, it should not be forgotten, at the galaxy cluster level with particular respect to x-ray clusters, that the correlation finds a problem. This was already noted by Milgrom in the early 1983 papers. In order to keep the MOND idea scale invariant, it was invoked that there were “dark” baryons responsible for the extra lensing. But this leads to a troubling question: What sources these dark baryons only in x-ray clusters but not elsewhere?

We have a few clues that might suggest that rather than assuming that the MOND constant never varies but certain hyperbolic interactions may lead to a factor multiplying a_0 so that the observed baryons in x-ray clusters can suffice to maintain the correlation without introducing additional “dark” baryons. The remarkable example where the lensing is greatly weakened is found at the “bullet” of the bullet cluster where little or no lensing is observed at distance from the bullet. In the opposite example, Jee and Mahdavi have observed an excess of lensing in a “dark” core of A520.
In both cases clusters of galaxies have had hyperbolic encounters with tell-tale x-rays helping to mark where ram gas was heated. It is this later possibility of darkening due to hyperbolic interactions with incidental production of x-rays that could be at the source of x-ray clusters not observing the strict MOND paradigm without needing an excess of “dark” baryons only to be found in x-ray clusters but not elsewhere. We have seen on the very small scale spacecraft occasionally exhibiting a hyperbolic interaction anomaly sometimes called the flyby anomaly, but typically occurs at larger galaxy scales with observed “dark” matter offsets not only of members of a galaxy cluster but also as “scars” of hyperbolic interaction between field galaxies and clusters also showing offsets in the field galaxies.

George
2016-Sep-26, 08:15 PM
It seems to me that the paper demonstrates that baryonic matter only fits nicely for the central zone and DM is needed thereafter to flatten the curve. Am I wrong? They show what looks like a 1 to 1 for the centripetal force (g) of both baryonic and observed, but only in the inner regions. Their Fig. 3 demonstrates this, I think.

They also suggest their derived fit for the centripetal curve relates to the MOND model, but by introducing a special acceleration term gt.

kzb
2016-Sep-27, 12:50 PM
It seems to me that the paper demonstrates that baryonic matter only fits nicely for the central zone and DM is needed thereafter to flatten the curve. Am I wrong? They show what looks like a 1 to 1 for the centripetal force (g) of both baryonic and observed, but only in the inner regions. Their Fig. 3 demonstrates this, I think.

They also suggest their derived fit for the centripetal curve relates to the MOND model, but by introducing a special acceleration term gt.

The key point of this paper is that there is an exact correspondence between baryons and the gravitational acceleration. This has been noted before, but there are now more precise numbers available to play with. The relation has no detectable intrinsic scatter even with the more precise observations. All scatter can be attributed to measurement uncertainties.

The central regions of dark-matter dominated low surface brightness galaxies map precisely on the same line as the outer regions of high surface brightness galaxies.

There is apparently a "conspiracy" between dark matter and baryons so that a smooth transition always occurs between the baryon dominated regions and the dark matter dominated regions. This applies to dwarf galaxies and giants.

A single equation can be fitted that applies to all spiral galaxies. You are correct that a special acceleration term is used in this equation.

All very mysterious.

George
2016-Sep-28, 02:12 PM
Kinda curious. Thanks!

Ultron
2016-Sep-28, 04:46 PM
Milgrom is maybe right in the case of galaxy rotations fitting to MOND prediction, but there is good chance that MOND has generally some unsolved problems in other areas than galaxy rotations. He is focusing so much on galaxy rotations, that MOND seems like ad hoc theory just for galaxy rotations.

borman
2016-Oct-08, 02:29 AM
Some additional information

Press releases:

Correlation between galaxy rotation and visible matter puzzles astronomers

http://physicsworld.com/cws/article/news/2016/oct/07/correlation-between-galaxy-rotation-and-visible-matter-puzzles-astronomers
Modified MOND could explain galaxy densities
http://physicsworld.com/cws/article/news/2016/sep/29/flash-physics-mond-explains-galaxy-densities-fusion-boss-resigns-and-university-fined-for-explosion

A companion paper:
The Relation between Stellar and Dynamical Surface Densities in the Central Regions of Disk Galaxies

https://arxiv.org/abs/1607.02145

Milgrom wrote in reference to this paper:
Universal MOND relation between the baryonic and `dynamical' central surface densities of disc galaxies

https://arxiv.org/abs/1607.05103

Another companion paper:
SPARC: Mass Models for 175 Disk Galaxies with Spitzer Photometry and Accurate Rotation Curves
https://arxiv.org/abs/1606.09251
Here is a Milgrom paper looking to ultra-diffuse cluster galaxies as a possible reservoir for cluster baryonic dark matter (CBDM):
Ultra-diffuse cluster galaxies as key to the MOND cluster conundrum
https://arxiv.org/abs/1508.04001
The idea is expressed that CBDM trapped in the gravity well of UDGs may not be ram stripped in the cluster-cluster collision of the Bullet cluster and so would travel with the galaxies. However some of the CBDM would be released into the intracluster medium from disrupted UDGs. Being baryons, these should be subject to ram stripping like the bullet gas. This would create more tension with the hypothesis of CBDM when there is not excess lensing associated with the bullet itself. The ram gas should be made of unbound intracluster gas from both clusters, including unbound CBDM from disrupted UDGs.

Squink
2016-Oct-08, 06:44 PM
This is hurtful. I had just been coming around to accepting that dark matter was a real thing;
and now we have to have the whole MOND argument all over again?
The bullet cluster was supposed to be the nail in the coffin.
Now the universe may be far emptier than we thought.
I suppose dark energy will come under assault too and we'll be stick with 1/5th of the stuff we thought was out there.
Slim pickings.
Of course, if the virial coefficient (https://en.wikipedia.org/wiki/Virial_coefficient) on Newton's law gives us a reactionless drive, that'll be some comfort.

George
2016-Oct-10, 06:02 PM
But doesn't MOND still require Dark Matter? IIRC, it reduces the amount of DM, but does not eliminate it. The paper, not that I understand it all that much, does not discount the requirement of DM in the outer disk regions.

Ultron
2016-Oct-11, 02:57 PM
Some additional information

Press releases:

Correlation between galaxy rotation and visible matter puzzles astronomers

http://physicsworld.com/cws/article/news/2016/oct/07/correlation-between-galaxy-rotation-and-visible-matter-puzzles-astronomers
Modified MOND could explain galaxy densities
http://physicsworld.com/cws/article/news/2016/sep/29/flash-physics-mond-explains-galaxy-densities-fusion-boss-resigns-and-university-fined-for-explosion

A companion paper:
The Relation between Stellar and Dynamical Surface Densities in the Central Regions of Disk Galaxies

https://arxiv.org/abs/1607.02145

Milgrom wrote in reference to this paper:
Universal MOND relation between the baryonic and `dynamical' central surface densities of disc galaxies

https://arxiv.org/abs/1607.05103

Another companion paper:
SPARC: Mass Models for 175 Disk Galaxies with Spitzer Photometry and Accurate Rotation Curves
https://arxiv.org/abs/1606.09251
Here is a Milgrom paper looking to ultra-diffuse cluster galaxies as a possible reservoir for cluster baryonic dark matter (CBDM):
Ultra-diffuse cluster galaxies as key to the MOND cluster conundrum
https://arxiv.org/abs/1508.04001
The idea is expressed that CBDM trapped in the gravity well of UDGs may not be ram stripped in the cluster-cluster collision of the Bullet cluster and so would travel with the galaxies. However some of the CBDM would be released into the intracluster medium from disrupted UDGs. Being baryons, these should be subject to ram stripping like the bullet gas. This would create more tension with the hypothesis of CBDM when there is not excess lensing associated with the bullet itself. The ram gas should be made of unbound intracluster gas from both clusters, including unbound CBDM from disrupted UDGs.

Good overview. But I think MOND is not realistic option in explaining these results. MOND is around already very long, but it has predicted nothing new except that they always modify it to fit rotation of galaxies. If MOND would predict accelerating expansion of Universe (a.k.a. Dark energy) before it was confirmed by observation, it would be an important argument in favor of MOND. But they didnt predicted it.

kzb
2016-Oct-12, 12:40 PM
If MOND would predict accelerating expansion of Universe (a.k.a. Dark energy)

Was dark energy predicted before the accelerating expansion was observed? Yes we had the cosmological constant but that was proposed for different reasons.

I agree that MOND is very empirical. If you make up an arbitrary equation to fit the data then of course it will look good.

loglo
2016-Oct-15, 06:06 AM
One rather unexpected cite of McGaugh's paper is from Lee Smolin.

" Four principles for quantum gravity"

https://arxiv.org/abs/1610.01968
" Four principles are proposed to underlie the quantum theory of gravity. We show that these suffice to recover the Einstein equations. We also suggest that MOND results from a modification of the classical equivalence principle, due to quantum gravity effects."

borman
2016-Oct-15, 10:42 PM
Smolin also cites reference 61 with respect to MOND bubbles at lagrangian points. One might also cite Ignatiev's MOND jerk term on Earth for a second at a specific location. What is suggested is that where the gravitational force is cancelled the modification should occur. These bubbles might be more rare since besides the Earth. Moon, and Sun contributions, Jupiter and even Saturn can give gravitational fields that exceed a_0. If the conditions arise and a test can be done, a null result (no jerk where there should be one) would falsify Smolin's atte,pt to link to MOND. Pure MOND usually does not go here and transition occurs when all fields are weaker than a_0 without regard to whether strong fields happen to cancel.

The only potential exception to the pure MOND idea is the trailing anomaly that adjuncts to the Pioneer Anomaly. The Pioneers are still deep in the solar well and Modified inertia would not explain either. Unlike the Pioneer anomaly which is about 2 pi larger than a_0, the trailing anomaly varies over time but peeks at a_0. The time variation is not steady but is typically varied around 300 days. There have been a couple papers that have tried to account for the variation but are theoretical outliers. What is not generally appreciated is that its maximum value is very close to a_0. Recovering a_0 within the sun's well might represent a de-screening process hypothesis: Only the sun produces a field in excess of a_0 out there, so the de-screening is maximal when the screen is between the craft and the sun. Variation would occur if the screen moves out of best alignment by a few degrees. From time to time, the HGA was commanded to point to Earth to improve signal acquisition. Sometimes the Earth would be roughly inbetween the Sun and the craft to give maximal de-screening and when the Earth is on either side of the sun, the minimal de-screening would occur. This might account for the not quite annual and not quite regular appearance of the signal. This hypothesis is falsified if the correlation to HGA adjustments fails.

George
2016-Oct-16, 11:45 PM
Was dark energy predicted before the accelerating expansion was observed?
Well, kinda. Lemaitre's 1934 paper states, "Everything happens as if the energy in vacuo would be different than zero...we associate a pressure p = -(ro)c2 to the energy of the vacuum...this is essentially the meaning of the cosmical constant." [From Robert Kirshner's 2012 forward in Hubble's book.] Lemaitre's paper, perhaps not his earlier work in which he translated if from French to English for Eddington, had a graph that showed the universe expanding, becoming static, then accelerating until it reached the Hubble constant. [Too bad he didn't keep going. :)] Lemaitre, early on, combined Slipher's velocities with Hubble's distances and suggested this relationship. By the time, however, he translated his original French work, Hubble had already improved all of this so he left it out of his English version, which he sent to Eddington, who quickly published it.

Jerry
2016-Nov-09, 08:17 PM
Milgrom is maybe right in the case of galaxy rotations fitting to MOND prediction, but there is good chance that MOND has generally some unsolved problems in other areas than galaxy rotations. He is focusing so much on galaxy rotations, that MOND seems like ad hoc theory just for galaxy rotations.Dark Matter was/is also an ad-hoc gravitational or material state used to explain deviations from Newtonian expectations. Dark matter is a place holder, not an explanation.

Jean Tate
2016-Nov-15, 02:25 AM
Bee's "Modified Gravity vs Particle Dark Matter. The Plot Thickens." blog post (link (http://backreaction.blogspot.com/2016/10/modified-gravity-vs-particle-dark.html)) is interesting (be sure to read the comments!), as are the (now quite a handful) of recent papers on this and closely related topics. :)

ShinAce
2016-Nov-19, 12:18 AM
Thanks for that link trinitree.

Just so no one misses it, I've started a sister thread from the theoretical side of things:
https://forum.cosmoquest.org/showthread.php?163035-Verlinde-s-entropic-gravity-is-back