Four billion years from now, after its first close pass through the Milky Way, a view of Earth's nighttime sky shows that M31 is tidally stretched out and the Milky Way is also warped (Image: NASA / STScI)
An image of the present day line-up for the collision between our Milky Way galaxy and the Andromeda galaxy. The galaxies are moving toward each other, and being accelerated by their mutual gravity (Image: NASA / STScI)
Before-and-after comparison of the size of our Milky Way galaxy at present, and after it merges with M31. The merged galaxies will form a large elliptical galaxy. Our Sun now orbits in the Milky Way's disk, but after the merger will be tossed into a highly elliptical orbit (Image: NASA / STScI)
This image describes how the transverse motion of M31 was measured by Hubble. As the galaxy drifts through space, its stars will move uniformly against the (essentially) fixed background galaxies (Image: NASA / STScI)
Astrophotograph of M31, also known as the Andromeda nebula, taken using an 85mm telescope with a hydrogen-alpha filter to enhance nebulosity (Photo: Adam Evans)
3.75 billion years from now - the nighttime sky showing the Andromeda galaxy (M31) early in its collision with our Milky Way galaxy (Image: NASA / STScI)
Mosaic image of Earth's nighttime sky as the collision of M31 and the Milky Way unfolds: 1. (Upper left): Present Day - the bright belt of our Milky Way stretches across the sky, while the Andromeda galaxy looks like a faint spindle, several times the diameter of the full Moon. 2. (Upper right): 2 Billion Years - M31's approaching disk is noticeably larger. 3. (2nd row left): 3.75 Billion Years - M31 fills the field of view. The Milky Way begins to show distortion due to tidal pull from Andromeda. 4. (2nd row right)-5(3rd row left): 3.85-3.9 Billion Years - during the first close approach, the sky is ablaze with new star formation, which is evident in a plethora of emission nebulae and open young star clusters. 6. (3rd row right): 4 Billion Years - After its first close pass, Andromeda is tidally stretched out. The Milky Way, too, becomes warped. 7. (Final row left): 5.1 Billion Years - During the second close passage, the two galactic cores maintain their separate identity. The level of star formation is much smaller because interstellar gas and dust has been reduced during earlier stages of the collision. 8. (Final row right): 7 Billion Years - The merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky.
This composite image shows a region in the halo in the neighboring Andromeda galaxy that astronomers used to precisely measure the galaxy's sideways motion on the sky (Image: NASA / STScI)
Two billion years from now, the disk of the approaching Andromeda galaxy is noticeably larger (Image: NASA / STScI)
During the first close approach just prior to four billion years in the future, the sky is ablaze with new star formation, which is evident in vast numbers of emission nebulae and open young star clusters (Image: NASA / STScI)
At 3.75 billion years, Andromeda fills the field of view, and the Milky Way begins to show distortion due to tidal pull (Image: NASA / STScI)
During the second close passage at 5.1 billion years, the cores of the Milky Way and M31 galaxies appear as a pair of bright lobes, while bright nebulae are sparse because interstellar gas and dust were largely depleted by the earlier collision (Image: NASA / STScI)
After seven billion years, the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky (Image: NASA / STScI)
This is a nighttime image of our Milky Way galaxy, which includes a view of M31, that lies 2.5 million light-years distant and looks like a faint spindle, several times the diameter of the full Moon (Image: NASA / STScI)
When Galaxies Collide! It sounds like an early science fiction novel. However, analysis of Hubble measurements shows that our own Milky Way galaxy is moving toward a head-on collision with our nearest neighbor, the Andromeda galaxy (also known as M31). The collision will start in about four billion years, and over the following three billion years the two spiral galaxies will coalesce into a large elliptical galaxy. Based on this data, NASA has produced a video of the upcoming collision.
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