Clues left at a galactic hit-and-run

Galactoseismology
guh-LAC-toe-saiz-MAHL-ah-jee  n.

The study of disturbances in a galaxy’s structure (essentially, galaxy quakes) to discover dark, but massive, cosmic objects.

KISSIMMEE, Fla. — Ripples in the Milky Way’s outer layers of gas were the first clue. Now, scientists suspect they have found a small, faint galaxy that brushed past our galaxy a few hundred million years ago. This dwarf galaxy doesn’t have many stars, but it is rich in dark matter, the invisible but predominant source of mass in the universe. Sukanya Chakrabarti, an astronomer at the Rochester Institute of Technology in New York, reported the findings January 8 at a meeting of the American Astronomical Society.

Chakrabarti first came up with the idea of a dwarf galaxy hit-and-run in 2009 as a way to explain the puzzling galactic ripples. In 2015, her team reported finding stars where she had predicted the runaway galaxy to reside, about 300,000 light-years away in the constellation Norma. Now, Chakrabarti says she has determined that three of the stars are speeding away at about 200 kilometers per second, compelling evidence that the stars are part of a gravitationally bound system bolting from the Milky Way.

The researchers still need more evidence to prove they have seen a dwarf galaxy. But if the finding is confirmed, it will mark the first use of galactoseismology to discover an object via the galactic crime scene it left behind.