Milky Way is Larger Than Predicted

For years, astronomers have thought that the Milky Way was a weak sister to the neighboring Andromeda galaxy in both the size and mass.

But last Monday, Mark J. Reid of the Harvard-Smithsonian Center for Astrophysics overturned this decades-long belief at the American Astronomical Society’s convention in Long Beach, California.

In a recently-released study, Reid and his colleagues used the Very Long Baseline Array to map the Milky Way in a more accurate, multi-dimensional way.

They proved that it is 15 percent larger and 50 percent more massive than previously hypothesized. The galaxy also appears to be spinning about 15 percent faster than traditionally argued.

Reid, a five-foot-five, 140-pound astrophysicist, said the difference in estimated size was the cosmic equivalent of him suddenly bulking up to the size of a six-foot-three, 210-pound NFL linebacker.

“Previously we thought Andromeda was dominant, and that we were the little sister of Andromeda,” Reid said. “But now it’s more like we are fraternal twins.”

The VLBA is a system of 10 radio telescopes scattered across and around North America that together provide a higher level of accuracy for astronomical measurements than previously available.

“These measurements use the traditional surveyor’s method of triangulation and do not depend on any assumptions based on other properties, such as brightness, unlike earlier studies,” said Karl M. Menten of the Max Planck Institute for Radio Astronomy in Bonn, Germany, a member of Reid’s team.

The telescopes’ antennae measured the brightest new stars in the Milky Way. Rather than just noting the locations where they were first observed, the scientists included the dimension of time in their cosmic map—something Reid said hasn’t been done before.

But our galaxy being larger than we thought is not necessarily the best news. According to the researchers, a bigger Milky Way means that we could be crashing violently into the Andromeda galaxy sooner than we believed—though that’s still billions of years from now.

—Staff writer YouHo T. Myong can be reached at ymyong@fas.harvard.edu