History of Andromeda Galaxy in Timeline

By Popular Timelines Editorial Team · Updated: October 2, 2025

The Andromeda Galaxy is a barred spiral galaxy, the closest major galaxy to our Milky Way. Also known as Messier 31, M31, or NGC 224, it spans roughly 152,000 light-years in diameter and resides approximately 2.5 million light-years from Earth. Its name originates from the constellation Andromeda, named after the Greek mythological princess.

1999: Detection of Microlensing Event PA-99-N2

In 1999, the microlensing event PA-99-N2 was detected in the Andromeda Galaxy. One explanation suggests gravitational lensing of a red giant by a star with a potential planet, with a mass 6.34 times that of Jupiter. If confirmed, it would be the first extragalactic planet. However, anomalies were later found.

2005: Discovery of a new type of star cluster

In 2005, astronomers discovered a new type of star cluster in the Andromeda Galaxy, containing hundreds of thousands of stars. These clusters are larger and less dense than globular clusters.

2006: Discovery of Globular Cluster 037-B327 (Bol 37)

In 2006, a massive globular cluster named 037-B327 (also known as Bol 37) was discovered. It was initially thought to be more massive than Mayall II and the largest cluster of the Local Group; however, further studies showed it is actually similar in properties to Mayall II.

2006: Discovery of satellite galaxies alignment

In 2006, it was discovered that nine of the satellite galaxies of Andromeda lie in a plane that intersects the core of the galaxy, suggesting a common tidal origin.

2012: Detection of a microquasar in the Andromeda Galaxy

In 2012, a microquasar, characterized by a radio burst emanating from a smaller black hole was detected in the Andromeda Galaxy. The black hole is located near the galactic center and has about 10 M☉. The microquasar was the first observed within the Andromeda Galaxy and the first outside of the Milky Way Galaxy.