Astrophysicists Detect Difference Between How Dark Matter Behaves in Theory and How It Appears to Act in Reality

The universe’s funhouse mirrors are revealing a difference between how dark matter behaves in theory and how it appears to act in reality.

Dark matter is the invisible glue that keeps stars bound together inside a galaxy. It makes up most of a galaxy’s mass and creates an invisible scaffold that tethers galaxies to form clusters.

Dark matter does not emit, absorb, or reflect light. It does not interact with any known particles. Its presence is known only through its gravitational pull on visible matter in space.

Although dark matter is lightly smeared throughout the universe, it is heaped in regions of space called galaxy clusters. Each of these massive clusters, held together by gravity, is made up of about 1,000 individual galaxies — each of which carries its own dollop of dark matter.

In a new study in the journal Science, Yale astrophysicist Priyamvada Natarajan and a team of international researchers analyzed Hubble Space Telescope images from several massive galaxy clusters and found that the smaller dollops of dark matter associated with cluster galaxies were significantly more concentrated than predicted by theorists.

The finding implies there may be a missing ingredient in scientists’ understanding of dark matter.

This Hubble Space Telescope image shows the massive galaxy cluster MACS J1206. Embedded within the cluster are the distorted images of distant background galaxies, seen as arcs and smeared features. These distortions are caused by the amount of dark matter in the cluster, whose gravity bends and magnifies the light from faraway galaxies. This effect, called gravitational lensing, allows astronomers to study remote galaxies that would otherwise be too faint to see. Several of the cluster galaxies are sufficiently massive and dense to also distort and magnify faraway sources. The galaxies in the three pullouts represent examples of such effects. In the snapshots at upper right and bottom, two distant, blue galaxies are lensed by the foreground, redder cluster galaxies, forming rings and multiple images of the remote objects. The red blobs around the galaxy at upper left denote emission from clouds of hydrogen in a single distant source. The source, seen four times because of lensing, may be a faint galaxy. These blobs were detected by the Multi-Unit Spectroscopic Explorer (MUSE) at the European Southern Observatory’s Very Large Telescope (VLT) in Chile. The blobs do not appear in the Hubble images. MACS J1206 is part of the Cluster Lensing And Supernova survey with Hubble (CLASH) and is one of three galaxy clusters the researchers studied with Hubble and the VLT. The Hubble image is a combination of visible- and infrared-light observations taken in 2011 by the Advanced Camera for Surveys and Wide Field Camera 3.
Credit: NASA, ESA, P. Natarajan (Yale University), G. Caminha (University of Groningen), M. Meneghetti (INAF-Observatory of Astrophysics and Space Science of Bologna), the CLASH-VLT/Zooming teams; acknowledgment: NASA, ESA, M. Postman (STScI), the CLASH team

“There’s a feature of the real universe that we are simply not capturing in our current theoretical models,” said Natarajan, a senior author of the study and a professor of astronomy and physics at Yale. “This could signal a gap in our current understanding of the nature of dark matter and its properties, as this exquisite data has permitted us to probe the detailed distribution of dark matter on the smallest scales.”

Astronomers are able to “map” the distribution of dark matter within galaxy clusters via the bending of light the galaxies produce — a concept called gravitational lensing. Like a funhouse mirror, gravitational lensing distorts the shapes of background galaxies that appear in telescope images of cluster galaxies. The higher the concentration of dark matter in a cluster, the more dramatic the observed lensing effects.

The researchers used images from NASA’s Hubble Space Telescope, coupled with spectroscopy from the European Southern Observatory’s Very Large Telescope, to produce high-fidelity dark-matter maps.

A 3D view of the data showed the presence of dark matter hills, mounds, and valleys. From this perspective, the mapped dark matter looks like a mountain range, with peaked regions. The peaks are the dollops of dark matter associated with individual cluster galaxies.

The especially high quality of the study’s data allowed the researchers to test whether these dark matter landscapes matched theory-based computer simulations of galaxy clusters with similar masses, located at roughly the same distances.

What they discovered was that the simulations did not show any of the same level of dark-matter concentration on the smallest scales — the scales associated with individual cluster galaxies.


Astronomers seem to have revealed a puzzling detail in the way dark matter behaves. They found small, dense concentrations of dark matter that bend and magnify light much more strongly than expected. Credit: NASA’s Goddard Space Flight Center

“To me personally, detecting a gnawing gap — a factor of 10 discrepancy in this case — between an observation and theoretical prediction is very exciting,” Natarajan said. “A key goal of my research has been testing theoretical models with the improving quality of data to find these gaps. It’s these kinds of gaps and anomalies that have often revealed that either we were missing something in the current theory, or it points the way to a brand-new model, which will have more explanatory power.”

Natarajan has spent more than a decade confronting theoretical models of dark matter with data from gravitational lensing. “The quality of data and the sophistication of models have only now converged to permit stress testing of the cold dark matter paradigm, and it has revealed a crack,” she said.

For more on this research:

Reference: “An excess of small-scale gravitational lenses observed in galaxy clusters” by Massimo Meneghetti, Guido Davoli, Pietro Bergamini, Piero Rosati, Priyamvada Natarajan, Carlo Giocoli, Gabriel B. Caminha, R. Benton Metcalf, Elena Rasia, Stefano Borgani, Francesco Calura, Claudio Grillo, Amata Mercurio and Eros Vanzella, 11 September 2020, Science.
DOI: 10.1126/science.aax5164

Natarajan said the team, which includes researchers from Italy, the Netherlands, and Denmark, plans to continue stress testing theories of the nature of dark matter. The study’s first author is Massimo Meneghetti of the Observatory of Astrophysics and Space Science in Bologna, Italy.

AstronomyAstrophysicsDark MatterYale University
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  • Howard Jeffrey Bender

    Another possibility, from a view of String Theory, is that Dark Matter appears to us as an effect of string/anti-string annihilations. As you may know, quantum mechanics requires that strings must be formed as pairs in the quantum foam – a string and an anti-string – that immediately annihilate each other. Quantum mechanics also requires both the string and anti-string to be surrounded by “jitters” that reduce their monstrous vibrating energies. What if this jitter remains for a fraction of an instant after their string/anti-string annihilations? This temporary jitter would be seen by us as matter for that instant before it too returns to the foam. That’s why we never see it – the “mass” lasts only for that instant but is repeated over and over and over, all over. Specifics on this can be found in my YouTube at https://www.youtube.com/watch?v=N84yISQvGCk

  • randome

    Uh-oh! Something besides dark matter that can’t be explained? Let’s call it…beige matter!

  • Jeremiah Johnson

    ”Dark matter is the invisible glue that keeps stars bound together inside a galaxy.”
    Not quite. A dark matter halo is what is proposed by some to cause the galactic rotation curve to rotate faster instead of slower on the outer edges, as observed. The first 5-10 parsecs rotate at near the predicted rotational velocity based on Kepler’s 3rd law. But the further out you go, the more it diverges. A dark matter halo – additional non-visible mass around the galaxy – is proposed to make the rotation match Kepler’s 3rd law. But it does no such thing in holding galaxies together. Galaxies can hold together just fine without a dark matter halo. Just the mass on the edges will have less rotational velocity.

  • Lasso a train

    The photo sure looks like a negitive of the remnants of a super nova hacked and then superimposed over another photo . Arent people awful?

  • Lasso a train

    Dear mr.howard bender
    If you believe that , watch this, nothing up my sleeve, now watch me pull a universe out of my hat.

  • RbtAvyakt

    Good work but it may be unable to explain dark matter because these data are taken from a decade on behalf of stress test we can’t say anything about Dark matter as it is Dark.

  • Yep

    So u ding dongs that cant see touch taste touch any of that claim u can guess what it is, yet when they tell me I habe a pea size tumor with all your magnificance science, it turns out to be a grapefruit size. And my mesinteric nodes that have been swollen for 35 years that reacwntly you actually declared to be an actual organ. But for 35 years told I was full of shyt when I said that area hurt to even touch cloth tell they did a p.e.t scan and still they dont know. I think you habe as much knoledge about space as the size of ur pekker. you tell the waitress till she finds out to little to late. Fnn dumb. Oh and did I mention im on medicare habe celiacs and took 7 years to figure out i had scurvy,and it was diagnosed by a psychologist because drs coupdnt figure it out.

  • xABBAAA

    … So! Now that there is more stuff, what is the dark matter?…