Hubble Space Telescope/NASA

Ring Around the Galaxy

In the beginning of the year, a previously unseen band of stars beyond the edge of the Milky Way galaxy was discovered by a team of scientists from Rensselaer, Fermi National Accelerator Laboratory, and the Sloan Digital Sky Survey (SDSS). The discovery could help to explain how the galaxy was assembled 10 billion years ago.

Hidden from view behind stars and gas on the same visual plane as the Milky Way, this ring of stars is approximately 120,000 light years in diameter, says Heidi Newberg, associate professor of physics, applied physics, and astronomy at Rensselaer and a co-lead investigator on the project.

The ring of stars is probably the largest of a series of similar structures being found around the galaxy. Investigators believe that as smaller galaxies are pulled apart, the remnants dissolve into streams of stars around larger galaxies. Gravity, primarily from unseen dark matter, holds the ring in a nearly circular orbit around the Milky Way.

“These stars may be what’s left of a collision between our galaxy and a smaller, dwarf galaxy that occurred billions of years ago,” says Newberg. “It’s an indication that at least part of our galaxy was formed by many smaller or dwarf galaxies mixing together.”

Evidence of this new unexpected band of stars hidden by the Milky Way comes from multi-color photo imagery of hundreds of square degrees of sky and hundreds of spectroscopic exposures from the Sloan Digital Sky Survey, the largest international collaborative astronomical survey ever undertaken.

For four years, Newberg and other scientists have been examining the distribution of stars in the Milky Way. At the outer edge of the galaxy in the direction of the constellation Monoceros (the Unicorn) they found tens of thousands of unexpected stars that altered then-standard galactic models.