New MOND Simulation: First Galaxy Formation Model in Milgromian Gravity

[fresh_42]

TL;DR Summary

The formation of exponential disk galaxies in MOND

There is a new paper on a MOND simulation, and the participating institutes provide some credence.

The formation and evolution of galaxies is highly dependent on the dynamics of stars and gas, which is governed by the underlying law of gravity. To investigate how the formation and evolution of galaxies takes place in Milgromian gravity (MOND), we present full hydrodynamical simulations with the Phantom of Ramses (POR) code. These are the first-ever galaxy formation simulations done in MOND with detailed hydrodynamics, including star formation, stellar feedback, radiative transfer and supernovae. These models start from simplified initial conditions, in the form of isolated, rotating gas spheres in the early Universe. These collapse and form late-type galaxies obeying several scaling relations, which was not a priori expected. The formed galaxies have a compact bulge and a disk with exponentially decreasing surface mass density profiles and scale lengths consistent with observed galaxies, and vertical stellar mass distributions with distinct exponential profiles (thin and thick disk). This work thus shows for the first time that disk galaxies with exponential profiles in both gas and stars are a generic outcome of collapsing gas clouds in MOND. These models have a slight lack of stellar angular momentum because of their somewhat compact stellar bulge, which is connected to the simple initial conditions and the negligible later gas accretion. We also analyse how the addition of more complex baryonic physics changes the main resulting properties of the models and find this to be negligibly so in the Milgromian framework.

https://arxiv.org/abs/2002.01941

As I understood it, they have tested mainly against disk galaxies. However, shouldn't it be tested against ring, ellipse galaxies and nebulas , too?

And a more general question about MOND:
How do MOND theories compare to GR? Do they imply a modification of GR, too?

 

[Vanadium 50]

I'm not entirely sure what we've learned from this. I don't think it's surprising that when you infer a law from observed collective behavior, and then simulated based on that inference you get the same collective behavior back out. I suppose it is a kind of consistency check.

However, shouldn't it be tested against ring, ellipse galaxies and nebulas , too?

Why? Perhaps more to the point, "how?" These are not rotationally supported, and perhaps more to the point, ring and ellipticals are the result of collisions - how does one model their history. "Nebula" is too vague a term to be sensibly discussed.

How do MOND theories compare to GR? Do they imply a modification of GR, too?

MOND theories are non-relativistic. They imply some modification of GR. TeVeS was an example of an attempt to make a relativistic MOND.

 

[hodgeman]

I don't understand, didn't the Bullet cluster rule out MOND? Why are people still working on it?

 

[zoki85]

I don't understand, didn't the Bullet cluster rule out MOND? Why are people still working on it?

My first impression was that (some) people were desperate due to fact that no dark matter was detected in Earth labs despite long lasting efforts. But, there are also people not paying attention to the issue of dark matter existence. As a matter of fact I watched a video where researcher supports both views: that dark matter exists and MOND(s) are required. Crazy

 

[Vanadium 50]

I don't understand, didn't the Bullet cluster rule out MOND?

Abell 520 is a reverse bullet cluster. Why are people still working on LCDM?

My first impression was that (some) people were desperate due to fact that no dark matter was detected in Earth labs despite long lasting efforts

It's bad enough that this thread was hijacked to a general MOND thread. But your "first impression" is completely wrong. MOND was developed almost 40 years ago by Moti Milgrom. At that time, very little was known about Dark Matter's nature, and no serious detection experiment had been designed, much less operated.

But, there are also people not paying attention to the issue of dark matter existence.

If you mean "scientists who should have", your message is gratuitous and insulting. If you mean "other than scientists who should have" it's misleading.

 

[Ibix]

I don't understand, didn't the Bullet cluster rule out MOND? Why are people still working on it?

My understanding is that MOND proponents pointed out that MOND breaks a lot of physicists' standard intuitions about how gravity works. The Bullet Cluster "rules out" MOND because there's a transparent something outside the galaxies doing gravitational lensing, which can be easily interpreted as a cloud of dark matter. But the long range behaviour of gravity in MOND means that the addition of gravitational fields from several galaxies in the cluster predicts that lensing area, although Newtonian gravity would not. In other words, MOND proponents say it's explicable if you apply MOND properly, which physicists who aren't MOND experts failed to do.

There are plenty of things that MOND can't explain, largely at cosmological scales and dark matter fits into a relativistic theory much better than MOND. But our continuing failure to detect dark matter directly isn't exactly a ringing endorsement of dark matter either. I don't think the book is yet closed.

 

[zoki85]

If you mean "scientists who should have", your message is gratuitous and insulting. If you mean "other than scientists who should have" it's misleading.

None.
I watched presentation where dynamics of some observed galaxy could be nicely explained by dark matter influence. Then that theorist explained how the same things in particular case could be equally well (or even better) explained by tuning parameters in the "Milgrom's Law equation"

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

Thread will remain closed.