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Zoom in on the black hole next door

T. Lauer / NOAO / NASA / ESA

A new Hubble Space Telescope image centers on the 100-million-solar-mass black hole at the hub of the neighboring spiral galaxy M31, or the Andromeda Galaxy, one of the few galaxies outside the Milky Way visible to the naked eye and the only other giant galaxy in the Local Group. This is the sharpest visible-light image ever made of the nucleus of an external galaxy.

The Hubble Space Telescope has captured the best view yet of the Andromeda Galaxy's nucleus — which is actually a double nucleus, thanks to the galaxy's supermassive black hole.

Andromeda is the nearest spiral galaxy to our own Milky Way, and the only galaxy outside our own that's visible to the naked eye. But it's not easy to see what's going on at the bright center of the spiral. Astronomer Tod Lauer of the National Optical Astronomy Observatory put together several exposures in blue and ultraviolet wavelengths from Hubble's Advanced Camera for Surveys to produce this ultra-sharp view.

The inset photograph tells the story: The black hole itself can't be seen, but it's near the center of a compact cluster of blue stars at the center of the inset. That cluster is surrounded by the double nucleus, an elliptical ring of older reddish stars in orbit around the black hole.

"When the stars are at the farthest point in their orbit they move slower, like cars on a crowded freeway," NASA says in its image advisory. "This gives the illusion of a second nucleus."

NASA notes that the blue stars in the cluster are no more than 200 million years old, and had to have formed close to where they are now. Such stars wouldn't last long enough to form somewhere else and move inward.

So how can stars form so deep within the black hole's gravitational field? That's what Lauer and other astronomers are trying to figure out.

Lauer presented the Hubble observations this week in Austin, Texas, at a meeting of the American Astronomical Society.

This zoom dives deep into the nucleus of the Andromeda galaxy. Credit: NASA, ESA, and G. Bacon (STScI)

More from the astronomy meeting:

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.