Sitting in the constellation Triangulum, the third largest galaxy of the Local Group is a stunning face-on spiral galaxy about half the size of the Milky Way. Home to 40 billion stars, the Triangulum Galaxy may play a role in the collision between Andromeda and our Galaxy!

The Triangulum Galaxy was first discovered by the Italian astronomer Giovanni Battista Hodierna, who described it in his work in 1654 as a “cloud-like nebulosity”. It was only a century later, in 1764, that Charles Messier included it in his catalogue as object 33 and to this day, the Triangulum Galaxy is referred to as M33.

Positioned slightly less than 3 million light-years away from Earth, M33 is the second-closer large galaxy to our own after the Andromeda Galaxy (M31); at half the size of the Milky Way, it is the third-largest galaxy in the Locap Group, and home to around 40 billion stars according to the latest estimations.

While this number is considerably lower than that of our own Galaxy (100 billion stars) and the Andromeda Galaxy (1 trillion), the Triangulum Galaxy has a star-formation rate 10 times that of Andromeda. Several regions of star formation were in fact detected in M33, with the largest of all (NGC 604) being one of the biggest in the Local Group.

The Triangulum Galaxy is a spiral galaxy whose structure implies it had few interactions with nearby galaxies and is therefore considered an “introvert” galaxy. However, in recent years scientist found mounting evidence that suggests that the Triangulum Galaxy may actually be orbiting the Andromeda Galaxy and could therefore be involved in the collision between Andromeda and the Milky Way, about 4.5 billion years from now.