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Many consider Andromeda, also known as Messier 31, to be a sister galaxy to our own Milky Way. At a distance of only 2.5 million light years away, Andromeda is relatively close to our Galaxy. It is also a spiral galaxy like the Milky Way, and has many similar characteristics. However, a new study using data from NASA's Chandra X-ray Observatory has pointed out some interesting differences between these two galaxies when it comes to black holes. After combining over 150 Chandra observations spread over 13 years, researchers discovered 26 new black hole candidates in Andromeda. This is largest number to date found in a galaxy outside our own. Falling into the stellar-mass category, these black holes form when the most massive stars collapse. The result is a black hole that typically has between five and ten times the mass of the Sun. Seven of these black hole candidates are within 1,000 light years of Andromeda's center, more than what is found near the center of our Milky Way's core. This highlights that although Andromeda and the Milky Way are alike in many ways, they do have their differences. Astronomers have long known that the bulge of stars in Andromeda is bigger as is the super massive black hole at its center. Now we know that it may be a better producer of small black holes as well.
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(Credit: NASA/CXC/J. DePasquale)

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