What if Dark Matter doesn’t exist? The unique prediction of “modified gravity” challenges the dark matter hypothesis

Messier 63 Galaxy Sunflower

The best example is the Sunflower galaxy (Messier 63 / NGC 5055) with the strongest external field of the SPARC galaxies, whose well-measured rotation curve shows a slightly decreasing behavior at large radial distances and can be accurately modeled. only with an external field effect. Credit: ESA / Hubble and NASA

The team of international collaborators detects the “external field effect”, a unique prediction for the WORLD, the rival hypothesis of dark matter.

An international group of scientists, including Case Western Reserve University’s Department of Astronomy, Stacy McGaugh, has published research claiming that a rival idea to the popular dark matter hypothesis more accurately predicts a galactic phenomenon that appears to defy classical rules of gravity.

This is significant, say astrophysicists, because it further establishes the hypothesis – called modified Newtonian dynamics (MOND), or “modified gravity” – as a viable explanation for a cosmological dilemma: that galaxies seem to impede the long-accepted rules of gravity. traced to Sir Isaac Newton in the late 1600s.

Mystery: For decades, we have measured gravitational attraction in space more than we think we should have – that there is not enough visible or known matter to explain everything.

So proponents of dark matter theorize that most of the known universe is actually made of material that does not interact with light, making it invisible and undetectable – but that this material is much of the gravitational pull between galaxies. It has been the predominant theory for almost 50 years.

MOND theory, a counter-explanation introduced by physicist Mordehai Milgrom of the Weizmann Institute (Israel) in the early 1980s, says that this gravitational attraction exists because the rules of gravity are slightly changed.

Instead of attributing the excess of gravitational attraction to unseen, undetectable dark matter, MOND suggests that gravity at low accelerations is stronger than pure Newtonian understanding would be expected.

In addition, MOND made a bold prediction: the internal movements of an object in the cosmos should depend not only on the mass of the object itself, but also on the gravitational attraction of all other masses in the universe – called the “external field effect” (EFE). ).

Milgrom said the findings, if solidly confirmed, would be “a smoking weapon that shows that galaxies are governed by altered dynamics, rather than respecting Newton’s laws and general relativity.”

150 galaxies tested for EFE

McGaugh and his collaborators, led by Kyu-Hyun Chae of Sejong University in South Korea, say they have detected this EFE in more than 150 galaxies studied.

Their findings were recently published in The astrophysics journal.

“The external field effect is a unique signature of MOND that does not appear in Newton-Einstein gravity,” McGaugh said. “This has no analogy in conventional theory with dark matter. Detecting this effect is a real scratch. “

The team of six astrophysicists and astronomers includes lead author Chae and other contributors from the United Kingdom, Italy and the United States.

“I worked on the assumption that dark matter exists, so this result really surprised me,” Chae said. “Initially, I was reluctant to interpret our own results in favor of MOND. But now I cannot deny that the results, as they stand, clearly support the WORLD, rather than the dark matter hypothesis. “

Analyzing rotating galaxies

The group analyzed 153 rotational curves of galaxies on the disk as part of their study. The galaxies were selected from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database created by another collaborator, Federico Lelli, during his postdoctoral studies at Case Western Reserve, McGaugh and co-author James Schombert of the University of Oregon.

In addition to Chae, McGaugh, Lelli and Schombert, the authors of the research were Pengfei Li of Case Western Reserve and Harry Desmond of University of Oxford.

The scientists said they deduced EFE by observing that galaxies in strong external fields slowed down (or showed decreasing rotational curves) more frequently than galaxies in weaker external fields – as only MOND predicted.

Lelli said he was initially skeptical about the results “because the effect of the external field on the rotation curves is expected to be very small. I spent months checking different systems. Finally, it became clear that we have a real and solid detection. “

McGaugh said skepticism is part of the scientific process and understands the reluctance of many scientists to see the WORLD as a possibility.

“I came from the same place as the dark matter community,” he said. “It simply came to our notice then that we could be so wrong. But Milgrom predicted this over 30 years ago with MOND. No other theory anticipated the observed behavior. “

Reference: “Testing the strong equivalence principle: detecting the effect of the external field in rotating galaxies” by Kyu-Hyun Chae, Federico Lelli, Harry Desmond, Stacy S. McGaugh, Pengfei Li and James M. Schombert, 20 November 2020, The astrophysics journal.
DOI: 10.3847 / 1538-4357 / abbb96

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