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March 2, 2016

Hundreds of millions of years ago, a galactic bowling ball rolled through the edge of the Milky Way galaxy. It scattered stars like bowling pins, triggered the birth of new stars, and created waves in the galaxy’s disk that are still rippling today.

That’s the picture outlined by Sukanya Chakrabarti, an astronomer at the Rochester Institute of Technology. She used the ripples in the Milky Way to trace their origin. She also predicted where the disrupting galaxy would be today — then found evidence of the galaxy itself.

Chakrabarti was using a new technique, known as galactoseismology. Just as geologists use earthquakes to probe Earth’s interior, astronomers can use “galaxy quakes” to learn about galaxies.

In this case, Chakrabarti traced the possible origin of ripples in the Milky Way’s disk. Her simulations showed that they were caused by a collision with a small but heavy galaxy. The simulations showed that today, that galaxy should be about 300,000 light-years away.

And last year, she discovered a possible culprit, just where it was expected. She found three pulsating stars inside a dwarf galaxy. The way the stars pulse reveals the distance to the galaxy. The galaxy is small and faint, but it appears to contain a lot of “dark matter,” so it’s heavy. Additional observations should reveal more about the galaxy — perhaps confirming that it triggered a “quake” in the Milky Way a long time ago.

We’ll talk about an even bigger galaxy quake tomorrow.

Script by Damond Benningfield

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