Milky Way Gobbling Up a Neighbor

Our Milky Way galaxy is a cannibal. A new view shows it is voraciously consuming one of its smaller galactic neighbors.

The violent stretching, ripping and swallowing of the neighboring Sagittarius galaxy is not visible to human eyes because that galaxy is on the other side of the Milky Way and is obscured by numerous stars and clouds of dust. But a new infrared view of the skies taken by the Two Micron All Sky Survey, or 2MASS, reveals the destruction in vivid detail.

The infrared maps, created using twin 1.3-meter telescopes in Arizona and Chile, filtered out foreground stars to bring the relatively tiny Sagittarius galaxy into view and show its stars being stripped away and “wrapping like a spaghetti noodle in a big flourish around the Milky Way,” said Steven Majewski, an astronomer at the University of Virginia and lead author of a report to be published Dec. 20 in the Astrophysical Journal.

“Sagittarius is wimpy,” he said. “It’s clear who’s the bully in the interaction.”

The nibbling away of stars is the slow death of the Sagittarius galaxy; it cannot hold itself together much longer and may already be dead, said Martin Weinberg, co-author of the study and a 2MASS team member at the University of Massachusetts, which runs the project with NASA’s Jet Propulsion Laboratory in Pasadena.

The discovery changes thinking on how the Milky Way has evolved. It was long thought that the galaxy formed some 13 billion years ago from a giant gas cloud and remained relatively stable in size. Now it appears it may be growing by consuming a series of smaller neighbors and giving new homes to their stars.

“Alien stars from another galaxy are raining down on us right now,” Majewski said.