Predicting Andromeda’s Satellites |
Using modified laws of gravity, researchers from Case Western Reserve University and Weizmann Institute of Science closely predicted a key property measured in faint dwarf galaxies that are satellites of the nearby giant spiral galaxy Andromeda.
The predicted property in this study is the velocity dispersion, which is the average velocity of objects within a galaxy relative to each other. Astronomers can use velocity dispersion to determine the accelerations of objects within the galaxy and, roughly, the mass of a galaxy, and vice-versa.
To calculate the velocity dispersion for each dwarf galaxy, the researchers utilized Modified Newtonian Dynamics, MOND for short, which is a hypothesis that attempts to resolve what appears to be an insufficient amount of mass in galaxies needed to support their orbital speeds.
MOND suggests that, under a certain condition, Newton’s law of gravity must be altered. That hypothesis is less widely accepted than the hypothesis that all galaxies contain unseen dark matter that provides needed mass.
“MOND comes out surprisingly well in this new test,” said Stacy McGaugh, astronomy professor at Case Western Reserve. “If we’re right about dark matter, this shouldn’t happen.”
McGaugh teamed with Mordehai Milgrom, the father of MOND and professor of physics and astrophysics at Weizmann Institute in Israel. Their study, “Andromeda Dwarfs in the Light of MOND” will be published in the Astrophysical Journal. continue reading