Milky Way

A 2010 photo of the Milky Way, seen from Minnesota.

The universe keeps ballooning. The farthest galaxy found so far - in June - is nearly 10 billion light years away.

But the Milky Way just might be svelte.

That's the recent finding of a group of astronomers led by the University of Edinburgh in a first-of-its-kind measurement of galaxy mass: Our home galaxy weighs only about half as much as the neighboring Andromeda, a galaxy similar to the Milky Way.

"We always suspected that Andromeda is more massive than the Milky Way, but weighting both galaxies proved to be extremely challenging," said university physicist and astronomer Jorge Penarrubia in a news release by the AAAS science society. They figured it out by measuring the relative motions.

The finding comes down to the "dark matter halo" - the cloud of dark matter enveloping a galaxy. Not that anybody knows what dark matter is. Theorists say that it's some kind of stuff that keeps the universe from expanding as rapidly as calculations say it should. Dark matter is out there for sure, the thinking goes. It's just invisible.

The mass weight finding puts a new twist into the whole enigma.

"What's weird about it is that you now have two widely different estimates for the mass of two really similar galaxies," said The Citadel physics professor Luke Sollitt. "If you were looking at both from afar they would look really similar - about the same size, the same structure, and so on. But the idea that Andromeda has a dark (matter) halo so massive as to make its total mass twice the Milky Way's suggests that in some ways, these two similar-looking objects may be really quite different."

Mind boggling? Imagine the researchers' perplexity. If invisible dark matter is stranger than they theorize, the universe itself is that much bigger a mystery.

For the average person though, one thing is plain. If dark matter isn't what the usual theories say it might be, "that leaves you with the more esoteric theories as likelier," Sollitt said. "Which is kind of cool: the universe might be just as weird as some folks think it is."

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