Dark matter proponents 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 responsible for much of the gravitational pull between galaxies. A counter statement introduced in 1983 by Israeli physicist Mordehai Milgrom, the MOdified Newtonian Dynamics (MOND) theory, says that this gravity exists because the rules of gravity have been slightly changed. Rather than attributing the excess gravity to an invisible, undetectable dark matter, MOND suggests that gravity is stronger at low accelerations than would be predicted by a pure Newtonian concept. In addition, MOND makes a bold prediction: the internal movements of an object in the cosmos must depend not only on the mass of the object itself, but also on the pull of all other masses in the universe – the so-called external field effect. Now astrophysicists from South Korea, the United Kingdom, and the United States report detection of this external field effect in 153 disk galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database.
Messier 63 (also known as M63, NGC 5055 and the Sunflower Galaxy), a spiral galaxy located about 29.5 million light years in the constellation Canes Venatici, has the strongest external field among the SPARC galaxies. Image credit: NASA / ESA / Hubble.
“The external field effect is a unique signature of MOND that does not occur in Newton-Einstein gravity,” said study co-author Dr. Stacy McGaugh, a researcher in the Astronomy Department at Case Western Reserve University.
“In conventional theory, this has no analogy with dark matter. Detection of this effect is a real head scraper. “
“I’ve been working with the hypothesis that dark matter exists, so this result really surprised me,” added lead author Dr. Kyu-Hyun Chae, a researcher in the Department of Physics and Astronomy at Sejong University.
“At first I was reluctant to interpret our own results in favor of MOND. But now I can’t deny that the results in their current form clearly support MOND rather than the dark matter hypothesis. “
The scientists analyzed 153 rotation curves of disk galaxies from the SPARC sample.
They deduced the external field effect by observing that galaxies in strong external fields slowed or displayed declining rotational curves more often than galaxies in weaker external fields, as predicted by MOND only.
“I was initially skeptical about the results, as the external field effect on rotational curves is expected to be very small,” said Dr. McGaugh.
“We checked various systems for months. In the end, it became clear that we had real, solid detection. “
“Skepticism is part of the scientific process and understands the reluctance of many scientists to view MOND as a possibility,” she added.
‘I came from the same place as the one in the dark matter community. It hurts to think we’re so wrong. But Milgrom predicted this with MOND more than 30 years ago. No other theory anticipated the observed behavior. “
The team’s paper is published in the Astrophysical Journal.
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Kyu-Hyun Chae et al. 2020. Testing the strong equivalence principle: Detection of the external field effect in rotation-assisted galaxies. ApJ 904.51; doi: 10.3847 / 1538-4357 / abbb96
This article is based on text from Case Western Reserve University.