The Andromeda Galaxy has a diameter of about 160,000 light-years, and is larger than the Milky Way galaxy, although recent studies suggest that it is less massive. The estimated mass of our own galaxy is about 1000 billion solar masses. According to a recent study in 2000 by Evans et al., M31 has a total mass of approximately 700 billion solar masses. M31 is located 2.5 million light-years away. This image of M31 (NGC 224) also shows two campanion galaxies: M32 (NGC221) and M110 (NGC 205). M31 is interacting gravitationally with M31 and has deformed one of the Andromeda Galaxy's spiral arms. The massive cluster of young blue stars shown in the lower left hand portion of this image has its own NGC number, i.e., NGC 206. Observations with the Hubble Space Telescope in 1991 revealed that the core of M31 has a double structure. This appears to be a smaller black hole of 55 million solar masses orbiting the massive black hole at the center of the galaxy. If that is correct, the two black holes may eventually spiral into each other and one day merge into a single massive central black hole, and in the process of doing so, create some spectacular fireworks for future inhabitants of our galaxy.
Charles Messier designated this galaxy as M31 in his catalog. Messier observed M31 several times and produced a drawing of the galaxy. At that time, Messier and others thought that M31 was a nebula. Interestingly, in 1785 William Herschel suggested that M31 may be a "sister of the Milky Way." M31 contains 35,000 known variable stars. The discovery of cepheids in M31 by Edwin Hubble in 1923 allowed us, for the first time, to actually measure the distance to the Andromeda Galaxy and conclusively demonstrate that it was, indeed, a sister galaxy of the Milky Way, just as Herschel had suspected 138 years earlier.
This LRGB CCD image was taken with a Takahashi Epsilon 180ED telescope using an SBIG ST-8XE CCD operating at f2.8. The data was acquired from my backyard in Scottsdale, Arizona on three separate nights.
M31 (NGC 224)
Constellation: Andromeda
RA: 00h 42m 44s Dec: +41d 16' 08" (J2000)
January 29 & 31 and February 2, 2009
Image by Sid Leach
Scottsdale, Arizona
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