There is also a chance it will collide with the Milky Way prior to the Milky Way and M31 merging into one another.

The team also concluded that M33 will miss the initial collision between the Milky Way and M31 however, it may eventually join and later merge with the combined Milky Way-M31 remnant galaxy.

Based on this work, the team concluded that the first collision will take place about 4 billion years from now, and that multiple collisions occurring between 4 billion and 6 billion years from now are required for the galaxies to completely merge into one final galaxy. They found that it is primarily moving in the direction along the line of sight between M31 and our vantage point near the Milky Way’s center (i.e., the transverse motion of M31 is low), meaning that the Milky Way and M31 are on a nearly head-on collision course. In 2012, a team based at the Space Telescope Science Institute published a study in which they used the Hubble Space Telescope to measure the proper motion of M31. In other words, it was unclear whether the Milky Way and M31 would collide head on or just miss each other. However, until 2012, the transverse motion of M31, or its proper motion across the sky as a function of time, was not yet measured, and the net direction of M31’s velocity toward the Milky Way was also unknown. Advanced technology has helped astronomers pin down the speed of M31 to nearly 250,000 mph (402,336 km/h). Since the early 1900s, it has been known that M31 is moving toward the Milky Way. Based on work using the Very Long Baseline Array, Hubble Space Telescope, and Gaia, we now believe M33 is a satellite galaxy of M31, analogous to the Large Magellanic Cloud (LMC) orbiting around the Milky Way. The third most massive member of the Local Group is the Pinwheel Galaxy in Triangulum.

Both of these galaxies, which are separated by about 2.5 million light-years, are also host to many tens of low-mass satellite galaxies that orbit around them. The Milky Way and M31 are the two most massive galaxies in the Local Group.

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