HONOLULU – A cluster of
young stars in the Milky Way is hanging out where it seemingly shouldn’t exist.

Our galaxy is enveloped in an extensive halo of
old stars and hot gas — gas which can’t cool down enough to clump together and
form new stars. And yet, a flock of
relatively new stars is hurtling through the halo
, researchers
reported January 7 during a news conference at a meeting of the American
Astronomical Society.

The star cluster is about 120 million years old
and sits about 94,000 light-years away from Earth. Astronomers found it by
sifting through data from the European Space Agency’s Gaia satellite for young stars
clumped together and moving in the same direction across the sky.

The cluster “didn’t have time to form somewhere
else, so it was probably born near where we see it,” said Adrian Price-Whelan,
an astrophysicist at the Flatiron Institute in New York City. “But how did it
form there, where there’s very little cold gas that you need in order to form a
new generation of stars?”

A clue, he said, lies with the Magellanic
Clouds, two satellite galaxies of the Milky Way. The cluster appears to be
speeding ahead of a stream of gas being torn from those galaxies by the Milky
Way’s gravity, suggesting that perhaps new stars are popping out of shredded
remains of these satellites.

If the cluster and the stream are connected,
they reveal unknown conditions in the halo, said David Nidever of Montana State
University in Bozeman at the same news conference. The stars appear to plow
ahead, while gas in the halo drags on the stream, slowing it down. Taking into
account the star cluster’s age and its 17,000-light-year distance from the
leading edge of the stream, Nidever said that gas in the halo
may be 10 times as dense
as previously thought.

Newfound star cluster in the Milky Way animation
A newfound star cluster (blue dots) sits far above the spiral disk of the Milky Way (white dots) and likely formed out of material from the Magellanic Clouds (purple dots), two satellites of our galaxy.A. Price-Whelan, Simulation by J. Hunt