Name: Marla Geha
Affiliation: Yale University
Marla Geha has different job titles depending on who’s asking. “If I’m on a plane, I tend to be a physicist,” she says. “Then nobody wants to talk to me.” When she feels the need to impress someone, she’s an astrophysicist. And when she doesn’t mind a two-hour conversation, she tells them she’s an astronomer.
Geha is, in fact, all three. Now a professor at Yale, Geha spends her days (and, of course, nights) trying to identify faint galaxies that probably formed earlier than the Milky Way. Simulations of the Milky Way’s evolution predict that there are about 1,000 such formations. When Geha came on the scene five years ago, astronomers had found just 11 of them. She and others believed that more existed, hidden from view because the galaxies were made mostly of dark matter, the term for whatever it is out there that emits no light but somehow accounts for 90 to 95 percent of the universe’s entire mass.
In the quest to solve the so-called missing-satellite problem, Geha pored over digital maps of the sky, looking for areas with unexpected concentrations of stars. Then she painstakingly measured the velocity of each star. To her amazement, she found that the stars were moving too quickly for their size—tantalizing evidence that dark matter might be tugging on them.
So far, Geha and her team have discovered 14 galaxies. She hopes to find enough to verify the reigning theory of how the universe formed, and perhaps along the way help other fields fully define dark matter. “Astronomers and particle physicists don’t talk to each other much,” she says. In the future, she’ll be the one starting the conversation. —Doug Cantorsingle page