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Hubble telescope observations highlight dark matter's weirdness

Once again, scientists have realized that when it comes to dark matter, they are missing a piece or two of the puzzle.

Dark matter makes up more than a quarter of the universe, scientists have realized, but they haven't yet learned how to see it directly. (The weird stuff doesn't emit, absorb or reflect light, hence the name.) So they turn to effects they can see, like the way a clump of dark matter warps space around it, tweaking our view of objects on the other side. But according to a new study, some tiny clusters are distorting space much more than scientists had expected.

"There's a feature of the real universe that we are simply not capturing in our current theoretical models," Priyamvada Natarajana, a theoretical astrophysicist at Yale University and a coauthor on the new research, said in a statement. "This could signal a gap in our current understanding of the nature of dark matter and its properties, as these exquisite data have permitted us to probe the detailed distribution of dark matter on the smallest scales."

Related: Dark matter and dark energy: The mystery explained (infographic)

These "galactic fireworks" are the colorful stars which make up the globular cluster NGC 1805, as seen in this photo taken by the Hubble Space Telescope. This cluster of thousands of stars is located out at the edge of the large Magellanic Cloud.

These "galactic fireworks" are the colorful stars which make up the globular cluster NGC 1805, as seen in this photo taken by the Hubble Space Telescope. This cluster of thousands of stars is located out at the edge of the large Magellanic Cloud.  (Image credit: ESA/Hubble & NASA, J. Kalirai; CC BY 4.0)

The scientists behind the new research wanted to check how current theoretical models of dark matter stack up with the roundabout observations we can gather of it. So they turned to galaxy clusters, which hide a huge amount of dark matter.

"Galaxy clusters are ideal laboratories to understand if computer simulations of the universe reliably reproduce what we can infer about dark matter and its interplay with luminous matter," Massimo Meneghetti, a cosmologist at the National Institute for Astrophysics in Italy and lead author on the new research, said in the statement.

The researchers used observations of three different galaxy clusters gathered by two instruments, the Hubble Space Telescope and the Very Large Telescope in Chile. The scientists mapped the dark matter within the clusters by noting how the material was warping light.

Among the large-scale distortions the astronomers were expecting to find, they also spotted smaller areas of warping, which they suspect mark the locations of individual, smaller cluster galaxies that hide concentrations of dark matter.

But when the researchers combined their map of dark matter with a model's predictions of what dark matter might look like in cluster galaxies, the two landscapes didn't line up. That means scientists still haven't cracked the puzzle of how dark matter behaves.

The research is described in a paper published today (Sept. 11) in the journal Science.

Email Meghan Bartels at mbartels@space.com or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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  • rod
    The space.com reported noted, "But when the researchers combined their map of dark matter with a model's predictions of what dark matter might look like in cluster galaxies, the two landscapes didn't line up. That means scientists still haven't cracked the puzzle of how dark matter behaves. The research is described in a paper published today (Sept. 11) in the journal Science."

    This report and follow up observations will be very interesting to review. Perhaps LCDM cosmology has some real holes in it (thus inflation too). Here are some other reports. https://phys.org/news/2020-09-hubble-ingredient-current-dark-theories.html
    Here is the paper cited. 'An excess of small-scale gravitational lenses observed in galaxy clusters', https://science.sciencemag.org/content/369/6509/1347, "Gravitational lenses in galaxy clusters The large mass of a galaxy cluster deflects light from background objects, a phenomenon known as gravitational lensing. The large-scale gravitational lens caused by the whole cluster can be modified by smaller-scale mass concentrations within the cluster, such as individual galaxies. Meneghetti et al. examined these small-scale gravitational lenses in observations of 11 galaxy clusters. They found small lenses that were an order of magnitude smaller than would be expected from cosmological simulations. The authors conclude that there is an unidentified problem with either prevailing simulation methods or standard cosmology." Science, this issue p. 1347

    "Abstract
    Cold dark matter (CDM) constitutes most of the matter in the Universe. The interplay between dark and luminous matter in dense cosmic environments, such as galaxy clusters, is studied theoretically using cosmological simulations. Observations of gravitational lensing are used to characterize the properties of substructures—the small-scale distribution of dark matter—in clusters. We derive a metric, the probability of strong lensing events produced by dark-matter substructure, and compute it for 11 galaxy clusters. The observed cluster substructures are more efficient lenses than predicted by CDM simulations, by more than an order of magnitude. We suggest that systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results."
    Reply
  • Jesuis Laplume
    An unstated assumption still being used by most Science types is that there 'was, IS and will be' no Top-down organizing fields in the universe. Always remember and re-verify unstated assumptions!

    If there really were such a Top-down field in place, even before the universe came into being with the development of the space-time grid, and it influenced how the universe was informed as it unfolded; ignoring the possibility of such a field is always going to have us distort our models to ignore what such a field could be doing.

    Then, of course, we would have to continuing to correct for the un-needed corrections which should not be there if such an initial, Top Down field 'was, Is and will be' included in our models and is 'In Forming' the evolution of the universe as we observe it to act.

    It is remarkably easy to fail to remember that we made possibly-unstated assumptions while developing the Context of issues. After all, to develop the total Context of an issue at hand, one needs Philosophy; and we are all taught (or were taught explicitly or implicitly), that no such fields were allowed! In other words there is an unstated Dogma involved. There should be no Dogmas in Science! None! Not Any!

    If the math doesn't work; check the founding assumptions! Every Single Time!
    Reply