A Black Hole Threw a Star Out of the Milky Way Galaxy

Dennis Overbye

There are fastballs, and then there are cosmic fastballs. Now it seems that the strongest arm in our galaxy might belong to a supermassive black hole that lives smack in the middle of the Milky Way.

Astronomers recently discovered a star whizzing out of the center of our galaxy at the seriously blinding speed of 4 million mph. The star, which goes by the typically inscrutable name S5-HVS1, is currently about 29,000 light-years from Earth, streaking through the Grus, or Crane, constellation in the southern sky. It is headed for the darkest, loneliest depths of intergalactic space.

The runaway star was spotted by an international team of astronomers led by Ting Li of the Carnegie Observatories. They were using a telescope in Australia for a study known as the Southern Stellar Stream Spectroscopic Survey — the S5. The star is about twice as massive as our own sun and ten times more luminous, according to Li.

Drawing on data from the European Space Agency’s Gaia spacecraft, which has charted the positions and motions of some 1.3 billion stars in the Milky Way, the astronomers traced the streaking star back to the galactic center. That is the home of a black hole known as Sagittarius A*, a gravitational monster with the mass of 4 million suns.

The astronomers hypothesize that the runaway star was once part of a double-star system that came too close to the black hole. One of the pair fell in, and the other was sling-shotted away at hyperspeed. The process, a three-body gravitational dance, was first predicted by Jack Hills, a theorist at Los Alamos National Laboratory, in 1988.

The dance with S5-HVS1 unfolded about 5 million years ago, according to Li and her team, which included Sergey Koposov of Carnegie Mellon University, lead author of a paper describing the results published Tuesday in the Monthly Notices of the Royal Astronomical Society.

The astronomers estimate that in about 100 million years the star will have exited the Milky Way entirely. It is yet another example of nature’s ability to mix things up — tossing comets from faraway stars into our solar system, and flinging ice, rock and who knows what else between the planets on asteroids.

Out there, drifting among the other galaxies of the Local Group, far from the crowded circumstances of its birth, the star called S5-HVS1 will exhaust its thermonuclear fuel in about 2 billion years, blow up and die, alone. Like some people going off to college, say, some stars leave home and never come back.

This article originally appeared in The New York Times.


© 2019 The New York Times Company