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The Andromeda Galaxy is 2 million light years from Earth and has more stars than the Milky Way, but recent measurements suggest the Milky Way may be more massive. The two galaxies may collide in five billion years, but it is no longer thought to be inevitable. Both galaxies are the largest in the Local Group, which contains about 30 galaxies. The Andromeda Galaxy was originally called the Great Andromeda Nebula and has been on star charts since 905.
The Andromeda Galaxy is the sister galaxy of the Milky Way. It is located 2 million light years from Earth. The Andromeda Galaxy has more stars than the Milky Way, totaling about 1 trillion, compared to our 200 – 400 billion. However, recent measurements suggest that the Milky Way may in fact be more massive, with a larger dark matter halo. Mass estimates for the Andromeda Galaxy are around 7.1×1011 solar masses.
It was thought that the Andromeda Galaxy and the Milky Way would inevitably collide over a long period of time. This is no longer thought to be the case, although the collision may occur. If it does, it will happen in five billion years. For the solar system, located in the galactic arms, this would not be a very extreme event: the density of stars in the vicinity would roughly double. Stellar collisions would remain rare, even though the collision of supermassive black holes located in galactic nuclei could release enormous amounts of energy.
The Andromeda Galaxy and the Milky Way are the largest galaxies in the Local Group, which contains about 30 galaxies in total, most of which are dwarf galaxies. Both of these galaxies have a barred spiral structure and the center of mass of the Local Group is located between them, which is why both galaxies are accelerating towards each other.
Before 1925, when Edwin Hubble demonstrated that the Andromeda object was another galaxy using Cepheid variable stars, Andromeda was called the Great Andromeda Nebula. The Andromeda Galaxy is one of the most distant objects that can be seen with the naked eye – the Triangulum Galaxy is the furthest, at 3 million light-years – and has been on star charts since the year 905, when it was observed and noted by the Persian astronomer Abd Al-Rahman Al Sufi. Originally, it was called “the little cloud”. The Andromeda Galaxy takes its name from the constellation in which it is located, Andromeda.
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