Milky Way could hold remnants of last galactic 'meal'

A hypothetical composite image of what a collision between the Milky Way and the M31 (or Andromeda) galaxy might look like

By Richard Stenger
CNN.com Writer

(CNN) -- Some celestial detective work strongly suggests that the Milky Way consumed a smaller galaxy billions of years ago. And relics of the massive meal could still exist in our galaxy, astronomers said Monday.

After observing 1,500 sun-like stars, an international team of scientists determined that the unusual movement and composition of certain stars could reveal the presence of the galaxy's last significant merger.

The researchers, hoping to expand the search to 10,000 stars, think that their galactic survey could shed light on the origins of the galaxy.

"The Milky Way is a fairly large galaxy and we believe it was formed by the merging of a number of smaller galaxies," said Johns Hopkins University physicist Rosemary Wyse in a statement.

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Wyse and fellow investigators in England and Australia are attempting to map the far reaches of the Milky Way. They are focusing their search on stars away from the thin central disk that dominates the galaxy.

A spiral galaxy with a thin disk of gas and stars, the Milky Way also has "a thick disk … puffed up to a higher scale height than the rest of the disk," Wyse said.

The extent of the "puffing up" suggests that the Milky Way last consumed a satellite galaxy when it was extremely young, around 10 billion years ago, according to the astronomical team.

Preliminary observations offer tantalizing hints that remnants of the galactic merger exist, the researchers said. They hope their expanded search will confirm the existence of the galactic fossils.

"Just as the tidal interactions between the moon and the Earth cause distortions, there's going to be tidal interactions as a satellite galaxy comes into the Milky Way, and those can be severe enough to actually tear mass off the outer parts of the satellite galaxy," Wyse said.

"Those stars should be left behind on an orbit that is similar to the orbit of the satellite galaxy at that time."

Such cosmic collisions could take place again in the future. Astronomers predict the Milky Way and Andromeda, the nearest galaxy, will crash into one another billions of years from now.

NASA image reveals a battle of galactic forces
November 14, 2000
Hubble records fireworks when galaxies collide
November 2, 2000
Chandra's X-ray vision of universe awes, puzzles
June 8, 2000

Rosemary Wyse
The Johns Hopkins University
The Anglo-Australian Observatory

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