The Collision Between the Andromeda and Milky Way Galaxies

Author: Silvia DiPaola

Editors: Ken Saito and Yuze Zhu

Artist: Daelah Nicholas

The Milky Way Galaxy is currently on a collision course with another celestial body: the Andromeda Galaxy. Andromeda is the only galaxy we can now see without the use of a telescope! It has a long distance to travel (2.5 million light-years), so it is likely to take around four billion years to crash into the Milky Way. Let’s delve into the fated collision of these galaxies and the future formation of Milkomeda!

In four billion years, life on Earth will no longer exist when the Milky Way and Andromeda collide. At this point, the sun will have grown and expanded so much that the Earth will become the same temperature as Mercury today. Liquid water will evaporate, and life on Earth as we know it will cease to exist. Although humanity may not be around to witness it, the galaxies are set to merge over time. This starts with the collision becoming a chaotic mess of stars, altering each other's orbits. Eventually, the two will combine into a stable mega-galaxy. Scientists are currently calling this future mega-galaxy Milkomeda.

As for the logistics of the collision, the Andromeda Galaxy is currently speeding towards us at a rate of 250,000 miles per hour. In 2 billion years, Andromeda will appear much larger on a clear night’s sky. According to the Hubble telescope's measurements, Andromeda will fill the sky in 3.75 billion years, and its gravitational pull will begin to distort the Milky Way. About 3.9 billion years from now (by NASA's estimate), the galaxies will make their first close pass. Because galaxies are mostly empty space, they will pass through each other with very few collisions between stars, if any at all. For around a billion years, the two galaxies will continue to come together and fly apart. This will result in the scrambling of stars and redrawing of constellations in both galaxies. It will also cause interstellar gases to compress, making areas around the galaxy glow brightly. This compressed gas or dust could also gradually collapse and form new stars. Eventually, after a billion years, the two galaxies will begin to merge. This will continue for another six billion years until the cores of each spiral-shaped galaxy form a single oval-shaped galaxy. The night sky will be filled with lights from the two galaxies' largest and oldest stars. The eventful collision of Andromeda and the Milky Way is not likely to cause the death of our solar system, but it may push it out farther from the new galaxy’s core. If there is still some kind of life on Earth at that time, they will witness a spectacular light show during that span of one billion years when the Milky Way and Andromeda merge begins!

Interestingly, the Andromeda Galaxy has a smaller neighbor called the Triangulum Galaxy (M33). It will join the collision as well, and it might even merge along with the Milky Way and Andromeda. There is a small chance that Triangulum will hit the Milky Way first, but astronomers are still unsure. More research and observations need to be done for a definitive answer.

It took almost a century for astronomers to uncover the true destiny of Andromeda and the Milky Way galaxies, but this is a very small time frame compared to the astronomical timeline. Though there would not be anybody left to witness it, we should expect their collision in four billion years. For all we know, there may even be another collision with Milkomeda in several billions of years!

Citation:

Dunbar, Brian. “NASA's Hubble Shows Milky Way Is Destined for Head-On Collision.”

NASA, NASA, www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html.

McFall-Johnsen, Morgan. “When the Andromeda Galaxy Crashes into the Milky Way, This Is

What It Could Look like from Earth.” Business Insider, Business Insider, 8 Nov. 2019,

www.businessinsider.com/nasa-images-milky-way-andromeda-galaxy-collide-2019-

11#but-by-the-time-andromeda-approaches-our-sun-will-have-become-a-white-dwarf-

and-bye-bye-life-on-earth-didier-queloz-a-physicist-and-nobel-laureate-said-on-twitter-

13.

Wall, Mike. “We Finally Know When Our Milky Way Will Crash Into the Andromeda

Galaxy.” Space.com, Space, 8 Feb. 2019, www.space.com/43267-milky-way-andromeda-

collision-later.html.

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