Collision caused rings around Andromeda

By Sara Goudarzi

Space.com staff writer

updated 3:49 p.m. ET Oct. 18, 2006

Our giant neighboring galaxy, Andromeda, was involved in a head on collision with the dwarf galaxy, M32, some 210 million years ago, scientists announced today.

Infrared images from NASA's Spitzer Space Telescope recently revealed a never-before-seen ring of dust within Andromeda.

The new ring and the presence of a previously observed outer ring suggest a disturbance that could have only been caused by a collision. Astronomers suspect that the impact was brought about by the dwarf galaxy Messier 32 (M32).

"These dust rings are like ripples in a pond," said lead study author David Block from University of the Witwatersrand, Johannesburg. "Plop a stone into water and you get an expanding series of rings or waves. Let a small galaxy collide nearly head-on with a larger one, and you will see waves or rings of gas and dust that propagate outward as a result of the violent gravitational interaction.”

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To recreate the impacts of the crash, the researchers used computer models. The simulations showed that M32 plunged through the disk of Andromeda along Andromeda's polar axis back when dinosaurs roamed the Earth.

In the crash, M32 lost more than half of its original mass and the much more massive Andromeda was disrupted.

Astronomers believe that Andromeda—currently 2 million light years away from the Milky Way—will collide with our galaxy in 5 billion to 10 billion years. The two will eventually join to form one large elliptical galaxy.

The study is detailed in the Oct. 18 issue of the journal Nature.

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