Destined to Collide

The Triangulum Galaxy, otherwise known as Messier 33, lies almost 3 million light-years from Earth, and is a near neighbor of the Andromeda Galaxy. The galaxy is imaged here by the Nicholas U. Mayall 4-meter Telescope, located at Kitt Peak National Observatory (KPNO), a Program of NSF NOIRLab. 

The Triangulum Galaxy is the third-largest member of the Local Group, a cluster of galaxies that includes our Milky Way and its closest neighbors. The Andromeda Galaxy is the largest member. The Triangulum Galaxy and Andromeda Galaxy have history together, but astronomers are still investigating the details. Their close proximity has caused some researchers to suggest that Triangulum is a satellite of the Andromeda Galaxy, not unlike the way the Moon is a satellite of the Earth — just on a much, much bigger scale. Alternatively, some researchers propose that these two galaxies may be independent and have simply brushed past each other, as evidenced by streams of stars and neutral hydrogen gas linking the two galaxies. However they have interacted, it’s probable that they will dramatically collide in 2.5 billion years, resulting in their consolidation and eventual evolution into a lenticular galaxy.