Hubble Observations Suggest a Missing Ingredient in Dark Matter Theories

[Cougar]

This recent release by NASA's Hubblesite is interesting in its possible implications.

A recent study of 11 hefty galaxy clusters found that some small-scale clumps of dark matter are so concentrated that the lensing effects they produce are 10 times stronger than expected. These concentrations are associated with individual cluster galaxies.

The finding is that "Dark matter in clusters is therefore distributed on both large and small scales," the small scales being individual galaxies, which apparently harbor a much higher concentration of dark matter than previously thought. (Of course, the cluster itself harbors its own concentration.)

The implication being, how have these "small-scale clumps of dark matter" come to be? Running the clock back, what particular circumstance, what change in the current theory, would have been necessary to yield these results after 12-13 billion years?

[publiusr]

I thought that oxygen might be some dark matter, IIRC

[borman]

Assuming tidal stripping can not close the gap, there may be a missing parameter for Dark Matter Intensity. There have been suggestions about dark matter self-interactions usually leading to some kind of destruction into gamma rays. The conservative Intensity interaction would make some dark matter darker or more intense at the expense of other dark matter brighter and weaker.

[kzb]

They also measured the rotation speeds of some of the massive individual galaxies in the cluster.

The article neglects to mention whether or not these rotation speeds are within expectations of the mass as measured by gravitational lensing:

Follow-up spectroscopic observations added to the study by measuring the velocity of the stars orbiting inside several of the cluster galaxies. "Based on our spectroscopic study, we were able to associate the galaxies with each cluster and estimate their distances," said team member Piero Rosati of the University of Ferrara in Italy.

"The stars' speed gave us an estimate of each individual galaxy's mass, including the amount of dark matter," added team member Pietro Bergamini of the INAF-Observatory of Astrophysics and Space Science in Bologna, Italy.

[Noclevername]

I thought that oxygen might be some dark matter, IIRC

Oxygen has known physical properties which do not match those observed in dark matter.

[kzb]

Assuming tidal stripping can not close the gap, there may be a missing parameter for Dark Matter Intensity. There have been suggestions about dark matter self-interactions usually leading to some kind of destruction into gamma rays. The conservative Intensity interaction would make some dark matter darker or more intense at the expense of other dark matter brighter and weaker.

I don't think this is relevant to this study. It is about gravitational lensing, which depends only on the mass.

I find it strange that the paper does not comment about the correspondence between the mass as measured by lensing and the mass as measured by rotation speed. These should match within experimental uncertainty, but we are not told if they do or not.

[borman]

Another new problem for the CDM paradigm?

A preprint from arxiv:
An excess of small-scale gravitational lenses observed in galaxy clusters
https://arxiv.org/abs/2009.04471

The authors point out this problem is independent of cusp-core, missing satellite, too-big to fail,and planes of satellite galaxies (pg. 8).

The problem is graphically shown in figure 3 (pg. 11)

They were looking for Galaxy-Galaxy Strong Lensing events and found an order of magnitude too many events than simulations based on current theory allowed. They tried adjustments to parameters to get 2-3 times more events but not close to an order of magnitude. A GGSL event is where a fore ground cluster is strong lensing a background galaxy which is also strong lensing. This happened too often in their observations of 11 clusters.

A possible clue for consideration comes the last two sentences from page 7:
“Fig. 4 shows that, in our lens models, observed galaxies have larger circular velocities than their simulated analogs at a fixed mass. This implies that dark matter sub-halos associated with observed galaxies are more compact than theoretically expected.”

So, how does one compact dark matter? Does it have an excited state allowing a higher energy density that looks like campacting? Is its inertia modified? Can it be compacted by means of tidal stripping? Can it occur in other places than a cluster core?

A study was done some time ago comparing field galaxies similar to cluster galaxies not in the cluster core. It was found cluster galaxies had a significantly smaller dark matter halo than their field counter parts. The CDM explanation was that upon falling into the cluster , the field galaxy dark matter halo was tidally stripped. Perhaps the stripped dark matter was deposited in the core increasing the surface density of dark matter energy to add to baryon surface density to get to the critical point where strong lensing can occur.

The above paper did mention that galaxies in the cluster core may be more capable of strong lensing than field galaxies (pg. 31).

If tidal stripping is insufficient to lead to the amount of compacting to explain the observations then an intensity parameter is suggested as one alternative.

[kzb]

Another new problem for the CDM paradigm?

A preprint from arxiv:
An excess of small-scale gravitational lenses observed in galaxy clusters
https://arxiv.org/abs/2009.04471

The authors point out this problem is independent of cusp-core, missing satellite, too-big to fail,and planes of satellite galaxies (pg. 8).

This could be yet more evidence that there are swarms of AU-sized gas clouds out there.

http://www.manlyastrophysics.org/Pro...ons/index.html

[Noclevername]

This could be yet more evidence that there are swarms of AU-sized gas clouds out there.

http://www.manlyastrophysics.org/Pro...ons/index.html

Why would they not be giving off EM?

[kzb]

Why would they not be giving off EM?

Accoding to their advocates, they are impossible to detect by direct radio emission. They are small and cold, consisting only of hydrogen and helium.

They are detected when they cause "extreme scintillation events" in the radio. Also, quasar microlensing is caused by these clouds. Check out the website at the link I gave above, it is all quite fascinating.

However, positing that the mystery observations in the topic under discussion are part of the phenomenology of these clouds is purely myself wondering out loud.

[Jerry]

"We suggest that hitherto undiagnosed systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results."

Whenever a solution is proposed that does not, in some way, tie the proposed matter to a local observable - for example, placing the matter within the measured or extrapolated attributes of the period table, you might as well be arguing about how many angels can dance on the end of a pin.