The Andromeda Galaxy is the closest spiral galaxy to the Milky Way and the largest galaxy in our Local Group. Located about 2.5 million light-years away, it is visible to the naked eye from Earth. Andromeda is on a collision course with the Milky Way and is expected to merge with it in about 4.5 billion years, forming a new, larger galaxy.
Image Source: NASA
It's the Largest Galaxy in the Local Group - While the Milky Way contains more mass due to its dark matter, Andromeda is actually wider (about 220,000 light-years across compared to the Milky Way's ~100,000 light-years).
It’s Moving Toward Us. - Unlike most galaxies that are redshifted, Andromeda is blueshifted because it is moving toward the Milky Way at around 110 km/s (68 miles per second).
It Contains a Trillion Stars - Andromeda is home to an estimated 1 trillion stars, more than double the number in the Milky Way.
Andromeda and the Milky Way Will Collide - In about 4.5 billion years, Andromeda and the Milky Way will merge to form a new galaxy, sometimes called "Milkomeda" or "Milkdromeda."
It Has a Supermassive Black Hole at Its Core - Like the Milky Way, Andromeda has a supermassive black hole at its center, with a mass of around 100 million times the Sun’s mass—much larger than our own Sagittarius A*.
It Has Two Nuclei - Observations show that Andromeda’s core has two bright centers, possibly due to a past collision with another galaxy.
It Has Several Satellite Galaxies - Andromeda is surrounded by at least 14 dwarf galaxies, including M32 and M110, which are slowly being absorbed.
It Was Once Thought to Be a Nebula - Before Edwin Hubble proved otherwise in 1924, astronomers believed Andromeda was a spiral nebula within the Milky Way.
It’s One of the Few Galaxies Visible to the Naked Eye - The Andromeda Galaxy (M31) is one of the farthest objects visible to the naked eye. Under dark, clear skies, it appears as a small, faint, fuzzy patch in the constellation Andromeda. You can spot it best in the autumn months (September to November) in the Northern Hemisphere and in darker locations far from city lights.
It's Formed by Galactic Cannibalism - Andromeda has absorbed several smaller galaxies in the past and continues to do so, contributing to its massive size.
Interested in other Galaxies? Click here to find out about the Milky Way. Our home Galaxy.