ANDROMEDA

Last updated: 18/06/2019

The Andromeda galaxy, also known as Messier 31, M31, NGC 224, and the Andromeda Nebula, is a spiral galaxy about 2.5 million light-years from Earth and is the closest major galaxy to the Milky Way. (our galaxy) 

In Greek mythology, Andromeda is the daughter of the Aethiopian king Cepheus. Cepheus is also a constellation, located in the northern sky.

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at a trillion solar masses (1012M☉). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%. This has been called into question by a 2018 study which cited a lower estimate on the mass of the Andromeda Galaxy, combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way. The Andromeda Galaxy has a diameter of about 220,000 light-years, making it the largest member of the Local Group at least in terms of extension, if not mass.

The number of stars contained in the Andromeda Galaxy is estimated at one trillion, or roughly twice the number estimated for the Milky Way. So there could be billions of exoplanets that orbit these stars. 

Scientists believe that the Milky Way and the Andromeda galaxies will collide in the future.

In 1885, a supernova (known as S Andromedae) was seen in Andromeda, the first and so far only one observed in that galaxy. At the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova and was named accordingly.

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