The Milky Way Galaxy Weighs In: Andromeda May be Twice as Fat

First Posted: Jul 30, 2014 07:14 AM EDT

How fat is our home galaxy, the Milky Way? It's hard to tell considering we're smack dab in the middle of it. Now, though, scientists have taken a closer look at our galaxy and our neighbor, Andromeda, and have found that the Milky Way may actually be less massive than expected.

In previous research, scientists believed that the Milky Way was more massive than Andromeda. This is partly because they were only able to estimate the mass of the Milky Way and Andromeda based on observations made using smaller satellite dwarf galaxies.

Yet these new findings seem to indicate that the Milky Way isn't as big as expected. In the new paper, the researchers demonstrate a new, more accurate method for measuring the mass of galaxies.  They culled the previously published data that contained information about the distances between the Milky Way, Andromeda and other close-by galaxies that reside in and outside an area called the Local Group.

The galaxies in the Local Group are bound together by their gravity. This means that while most galaxies are moving apart due to expansion, the galaxies in the Local Group are actually moving closer together due to gravity. In this case, the researchers combined information about gravity and expansion to calculate the masses of the Milky Way and Andromeda.

"Historically, estimations of the Milky Way's mass have been all over the map," said Matthew Walker, one of the researchers, in a news release. "By studying two massive galaxies that are close to each other and the galaxies that surround them, we can take what we know about gravity and pair that with what we know about expansion to get an accurate account of the mass contained in each galaxy. This is the first time we've been able to measure these two things simultaneously."

The findings reveal that Andromeda actually has twice as much mass as the Milky Way and that both galaxies are made up of 90 percent of dark matter. This research could help scientists better estimate the physics of our universe in the future.

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.

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