Remote star clusters discovered on edge of Milky Way

Two clusters of stars have been found in a cloud hovering on the outskirts of the galaxy. Thousands of light-years from the spiral arms of the Milky Way, the clusters are the most distant ever observed in the galaxy, scientists report online February 26 in the Monthly Notices of the Royal Astronomical Society.

“Now we know that star formation may occur in remote regions of the Milky Way and not only in the galactic disk,” says Denilso Camargo, a coauthor of the new paper and astronomer at the Federal University of Rio Grande do Sul in Porto Alegre, Brazil.

Stars form inside masses of gas called molecular clouds. Most stars in the Milky Way take shape within the spiral arms that make up the galaxy’s main disk. But the new star clusters lie about 16,000 light-years from the disk.

Camargo and his team discovered the star clusters, designated Camargo 438 and 439, inside a molecular cloud called HRK 81.4-77.8. The astronomers also found more than 400 other star clusters near or inside of the Milky Way’s arms.

The team is still investigating how the star-forming cloud housing Camargo 438 and 439 strayed so far. Supernovas could have hurled the gas and dust that formed the cloud out of the Milky Way, or the material could have drifted in from outside the galaxy, says Camargo.