Did you need another existential risk to keep you up at night? Probably not, but here it is anyway: galaxy quakes. We’ve known about ‘em for years, and we hadn’t a clue what causes them—until now.
The culprit, unveiled today at the 227th meeting of the American Astronomical Society, is about as weird as you’d expect. Astronomers now believe that ripples in gas around the edge of the Milky Way are the result of a dwarf galaxy filled with dark matter ramming up against us several hundred million years ago.
Sukanya Chakrabarti of the Rochester Institute of Technology reached that bizarre conclusion by measuring the speed of three bright stars, called Cepheid variables, at the Gemini Observatory in Chile. These stars, which are suspected to hail from a larger population that entered our Milky Way during the Great Galactic Quaking of 300 million B.C., are all speeding away from us at about 450,000 mph.
“This really implicates these stars as being part of an organised, fast-moving system which we believe is a dwarf galaxy. It’s also very likely that this dwarf satellite brushed our galaxy millions of years ago and left ripples in its wake,” said Chakrabarti.
In addition to solving the galaxy quake mystery, Chakrabarti’s discovery highlights a promising new method for studying the dark matter that makes up nearly 30 per cent of our universe. Dark matter can be probed indirectly by measuring the velocity of objects moving through it—in this case, Cepheid variable stars.
One asteroseismological mystery down, one tremendous cosmological puzzle to go.
Top: Milky Way Galaxy, via Wikimedia
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