It looks as though that in about three billion years, we'll need a new revised, Hitchhiker's Guide to Galaxy. According to recent research the Andromeda Galaxy may be destined to collide with the Milky Way.
Andromeda, a spiral galaxy approximately 2.5 million light-years away in the constellation Andromeda is the nearest spiral galaxy to our own, the Milky Way. Andromeda and the Milky Way are approaching one another at a speed of 100 to 140 kilometers per second (62–87 miles/sec). However, this does not mean it will definitely collide with the Milky Way, since the galaxy's tangential velocity is unknown. If they do collide, the two galaxies will likely merge to form a monster elliptical galaxy.
Andromeda, home to the evil Kelvans in an early Star Trek episode, was believed to be the largest galaxy of the Local Group of galaxies, which consists of the Andromeda Galaxy, the Milky Way Galaxy, and the Triangulum Galaxy, and about 30 other smaller galaxies. But scientists now believe that the Milky Way contains more dark matter and may be the most massive in the grouping.
However, recent observations by the Spitzer Space Telescope revealed that Andromeda contains one trillion stars, greatly exceeding the four billion stars in our own galaxy. The wide, detailed Spitzer Space Telescope view of Andromeda at the top of the page features infrared light from dust (red) and old stars (blue).
This X-ray image, made with the Chandra X-Ray Astronomy Center's Advanced CCD Imaging Spectrometer, shows the central portion Andromeda. The Chandra X-ray Observatory is part of NASA's ﬂeet of "Great Observatories" along with the Hubble Space Telescope.
The blue dot in the center of the image is a "cool" million degree X-ray source where Andromeda's massive central object, with the mass of 30 million suns, is located, which many astronomers consider to be a super-massive black hole. Most of these are probably due to X-ray binary systems, in which a neutron star (or perhaps a stellar black hole) is in a close orbit around a normal star.
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