M33

The Triangulum Galaxy is a spiral galaxy in the constellation Triangulum. It is located at a distance of 3 million light-years from Earth and has a diameter of about 50,000 light-years. M33 is the third largest galaxy in the Local Group, which contains the Andromeda Galaxy (M31), the Milky Way, and about 44 other smaller galaxies. It is believed that M33 contains 40 billion stars, which is significantly fewer than in the two other large galaxies in the Local Group - the Milky Way Galaxy has about 400 billion stars, while the Andromeda Galaxy contains a trillion.
M33 may be a distant satellite of the Andromeda Galaxy: depending on the mass of the latter, M33 could have already completed one orbit around the Andromeda Galaxy, or the first close approach of these two galaxies is yet to occur.
The Triangulum Galaxy will participate in the collision of the Milky Way and the Andromeda Galaxy, which will occur in 4 billion years - there is a small probability that M33 will collide with our Galaxy before the Andromeda Galaxy does.
A unique feature of the Triangulum Galaxy is the absence of a massive black hole at its center.