A galaxy not so far away

Even though we’re in it, the Milky Way remains mysterious.

By Neela Pal (English, Foreign Affairs ’06)
Rachael Beaton

Beaton.
Photo by Tom Cogill.

The Galaxy, our Galaxy, may seem established and reliably stable, but it hasn't always been that way. And according to Rachael Beaton (Mathematics, Astrophysics '07), its future remains a mystery.

"It's easy to think of the Universe as static, because the timescale for change beyond the orbits within our solar system is so long that little occurs during one lifetime," she says. "This, however, is not the case. The Universe is not a static system; even the largest structures are constantly evolving."

Beaton has devoted her time at the University to developing new understandings of the "wild past" and unpredictable future of the Milky Way. But rather than studying the Milky Way directly, Beaton turned to Andromeda, the nearest spiral to ours, as the subject of her research.

"When people think of the Milky Way, our Galaxy, people assume we know a lot about it because we're in it," she says. "That's not true at all. There's a lot we don't know about it because we're inside it."

The unique vantage point of looking outward into the Galaxy from the Earth poses significant challenges for researchers, who are unable to see beyond the brightness of what Beaton calls a galactic bulge filled with starlight. Learning about Andromeda, which functions as the Milky Way's twin for researchers, therefore becomes crucial to developing understandings of our own Galaxy.

The utility of Andromeda in studying the Milky Way has itself been a question in flux. For while researchers had initially turned to Andromeda as a potential model, the discovery in the 1990s of a "bar" — "a heavy concentration of stars that extend from the center of the Galaxy in a rod or bar-like shape" — in the Milky Way disrupted former perceptions of the pair's similarities.

The research of Beaton and her Andromeda team — the astronomy department's Galactic Structure Research Group, led by Beaton's adviser, Steven Majewski, associate professor of astronomy  — is a crucial step toward reinstating the historical parallel between the two galaxies. What Beaton and Co. have uncovered is a stellar bar in Andromeda, which makes it, once again, a useful counterpart of the Milky Way for future researchers. The data that allowed this breakthrough finding in fact resulted from the work of U.Va. astronomy professor Michael Skrutskie, who led the new large-area survey of the Galaxy in infrared light as part of the Two Micron All-Sky Survey.

"It's really taken off, because what the data shows very clearly and obviously is that Andromeda is barred as well," Beaton says. "There's never been a photo with the conclusive image we have."

For Beaton, the exciting discovery of Andromeda's similarity to the Milky Way only introduces a whole new set of research questions.

For example, studying Andromeda can potentially provide insight into the origin and effects of dark matter. Named after its puzzling characteristic of not emitting light, dark matter remains a point of mystery for astronomers. Some scientists believe that dark matter is introduced into the Milky Way by dark galaxies that have been "eaten" by our Galaxy through a process known as "galactic cannibalism." Others forecast that dark matter will play a major role in the end fate of the universe. Given the staggering portion of both galaxies dark matter is believed to occupy — over 90 percent — Andromeda offers an opportunity to demystify this widespread phenomenon.

A question of particular intrigue for Beaton is why the Milky Way and Andromeda's appearances are a near match.

"It's just like a mirror; it's like we're looking back at ourselves," Beaton says. "Given the many random things that happen in the lives of galaxies it seems improbable to have two nearby galaxies look so similar."