It’s an astronomical version of “the rich get richer.” M33, the Triangulum galaxy, is being assimilated by the much larger Andromeda galaxy, M31. Eventually, M33 is likely to be completely absorbed by M31.
M33 is the third-largest member of the Local Group — a collection of dozens of galaxies that travel through space together. Andromeda and our own galaxy, the Milky Way, are the largest members of the group.
M33 is about half as wide as the Milky Way, and contains only about 10 percent as many stars. In photographs, it looks a bit like an octopus doing a pirouette, with spiral arms twirling around its center.
The arms are decorated with bright blobs of newborn stars. In fact, M33 contains one of the largest and brightest stellar nurseries in the entire Local Group — it’s given birth to tens of thousands of stars.
A long streamer of stars and gas extends from M33 toward M31, which is about a million light-years away. Simulations show that the galaxies may have sideswiped each other a couple of billion years ago. M31’s gravity pulled out the giant streamer, and captured some of M33’s stars for its own.
Simulations also show that the two galaxies will merge — perhaps in as little as a couple of billion years, with M31 absorbing the smaller galaxy.
Script by Damond Benningfield, Copyright 2013