A modified law of gravity correctly predicted, in advance of the observations, the velocity dispersion—the average speed of stars within a galaxy relative to each other—in 10 dwarf satellite galaxies of the Milky Way’s giant neighbor Andromeda.
The relatively large velocity dispersions observed in these types of dwarf galaxies is usually attributed to dark matter. Yet predictions made using the alternative hypothesis Modified Newtonian Dynamics (MOND) succeeded in anticipating the observations.
Stacy McGaugh, professor of astronomy at Case Western Reserve, and Mordehai Milgrom, the father of MOND and professor of physics at Weizmann Institute in Israel, report their findings, which have been accepted for publication by the Astrophysical Journal, in a preprint online: https://arxiv.org/abs/1308.5894.
The researchers tested MOND on quasi-spherical, very low-surface brightness galaxies that are satellites of Andromeda. In the cosmic scale, they are among the smallest galaxies, containing only a few hundred thousand stars. But with conventional gravity, they are inferred to contain huge amounts of dark matter.
“Most scientists are more comfortable with the dark matter interpretation,” McGaugh said. “But we need to understand why MOND succeeds with these predictions. We don’t even know how to make this prediction with dark matter.”
While this study is very specific, it’s part of a broader effort to understand how the universe, the Milky Way and Earth formed and what it’s all made of. This informs human understanding of our place in the universe, McGaugh said. Such issues have been of such importance that they’ve changed religion and philosophy over the centuries, sometimes sending people to be burnt at the stake.
Read more at: Phys.org