PROVIDENCE, R.I. [Brown University] — In the mid-1960s, an astronomer named Vera Rubin found something very strange about the way galaxies rotate.
Stars near the outer edges of galaxies orbited the center much faster than expected — so fast, in fact, that they should just fly off into space. The finding suggested that gravity from some enormous yet unseen mass is holding these galaxies together.
Rubin’s results were eventually confirmed, and the quest to understand the missing mass of the universe — dark matter — began in earnest. The quest goes on today, with Brown physicists playing key roles in solving what many see as the greatest mystery in modern physics.
Scientists think dark matter is the dominant form of mass in the universe, though no one is quite sure what the stuff actually is. The current consensus is that it’s some kind of particle, the leading candidate being the WIMP, or weakly interacting massive particle. WIMPs, according to theory, should have a mass of somewhere between 10 and 1,000 times the mass of a proton, as well as a snobbish tendency to avoid any interaction with normal matter (hence “weakly interacting”). And so they waft ghostlike through space, ubiquitous yet unseen.
“You and I and all the stuff we can touch and see, that’s just flotsam and jetsam in a vast sea of dark matter,” said Rick Gaitskell, a professor at Brown and a leading dark matter hunter. “Yet, because the particles are so weakly interacting, they pass right through us all the time and we never know they’re there.”