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Andromeda, Milky Way galaxies on collision course

Hubble scientists predict smash in 4 billion years

By Matthew Hay Brown, The Baltimore Sun

8:03 PM EDT, May 31, 2012

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First, the bad news: The Andromeda galaxy, an agglomeration of 1 trillion stars that is visible to the naked eye, is hurtling through space at 250,000 miles per hour — and it's coming right at us.

What's more, NASA astronomers in Baltimore said Thursday, while Andromeda barrels into our Milky Way, a companion galaxy will join in what the space agency is billing as a "titanic collision."

Now, the good news: With Andromeda still 2.5 million light years away, the collision won't take place for another 4 billion years, the astronomers said.

Simulations indicate that our solar system will probably be tossed much farther from the galactic core than it is today, NASA said, but the sun and the Earth and the other planets are in no danger of being destroyed.

The predictions were made possible by camera upgrades to the Hubble Space Telescope, operated by the Space Telescope Science Institute in Baltimore, which observed sections of the galaxy over a five- to seven-year period.

It has long been known that Andromeda, also known as M31, was moving toward the Milky Way. But it was not known whether the galaxies would collide or pass each other by.

Despite attempts dating back more than a century, astronomers had been unable to measure Andromeda's sideways motion in the sky, until now.

"We at last have a clear picture of how events will unfold over the coming billions of years," said Sangmo Tony Sohn, an astronomer at the institute.

"Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy," said Roeland van der Marel, who led the Hubble team.

The observations and the consequences of the merger are to be reported in a forthcoming issue of the Astrophysical Journal, NASA said.

matthew.brown@baltsun.com

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