Andromeda–Milky Way collision facts for kids
The Andromeda–Milky Way collision is a huge space event predicted to happen in about 4.5 billion years. This is when the two biggest galaxies in our local neighborhood—the Milky Way (where our Solar System and Earth are) and the Andromeda Galaxy—will crash into each other. Even though the galaxies will collide, the stars inside them are so far apart that it's very unlikely any individual stars will actually hit each other. The new galaxy formed from this collision is often called Milkomeda or Milkdromeda.
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Will It Really Happen?
The Andromeda Galaxy is currently rushing towards the Milky Way at about 110 kilometers per second. For a long time, scientists weren't sure if a collision was definitely going to happen. It was hard to measure the sideways movement of Andromeda.
But in 2012, researchers used the Hubble Space Telescope to look at stars in Andromeda. They compared their positions in 2002 and 2010. By studying thousands of stars, they found that Andromeda's sideways movement is very small. This means it's almost certainly going to merge with the Milky Way in about 5 billion years.
Galaxy collisions are actually quite common over the long lives of galaxies. Andromeda, for example, is thought to have crashed into at least one other galaxy before. Also, several smaller dwarf galaxies are currently colliding with and joining the Milky Way.
Scientists also think that the Triangulum Galaxy, which is the third-largest galaxy in our Local Group, will also be part of this huge collision. It will probably end up orbiting the new Milkomeda galaxy and eventually merge with it much later.
Will Stars Crash?
The Andromeda Galaxy has about 1 trillion stars, and the Milky Way has about 300 billion stars. Even with so many stars, the chance of any two stars actually hitting each other is tiny. This is because stars are incredibly far apart.
For example, the closest star to our Sun is Proxima Centauri. It's about 4.2 light-years away. To imagine this distance, if our Sun were a ping-pong ball, Proxima Centauri would be a pea about 1,100 kilometers away! The Milky Way itself would be about 30 million kilometers wide.
Even near the centers of galaxies, where stars are closer, the average distance between them is still huge. It's like having one ping-pong ball every 3.2 kilometers. So, it's extremely unlikely that any two stars from the merging galaxies will ever collide.
What About Black Holes?
Both the Milky Way and Andromeda galaxies have a giant supermassive black hole at their centers. The Milky Way has Sagittarius A*, which is about 3.6 million times the mass of our Sun. Andromeda has an even bigger one, about 200 million times the Sun's mass.
When the two galaxies merge, these two supermassive black holes will slowly move towards each other. This process could take millions of years. As they get closer, they will start to send out powerful gravitational waves. These waves will carry away energy, causing the black holes to spiral even closer until they finally merge into one giant black hole.
When this happens, gas falling into the new super-black hole could create a very bright quasar. This would release as much energy as 100 million supernova explosions!
Our Solar System's Future
Scientists have looked at what might happen to our Solar System during this collision. They predict there's a 50% chance that our Solar System will end up much farther from the center of the new galaxy than it is now.
There's also about a 12% chance that our Solar System could be completely thrown out of the new galaxy during the collision. If this happens, it wouldn't harm our Sun or planets directly.
However, long before the galaxies collide, Earth will already be too hot for liquid water to exist on its surface. This is expected to happen in about 0.5 to 1.5 billion years. The Sun will gradually get brighter, making Earth too hot for life as we know it.
New Star Formation
When two spiral galaxies like the Milky Way and Andromeda collide, the gas and dust in them get squeezed together. This can cause a burst of new stars to form, like what we see in the Antennae Galaxies.
In the case of the Andromeda–Milky Way collision, scientists think there won't be much gas left in the galaxies' disks. So, the burst of new stars might not be as strong. However, it could still be enough to create a quasar at the center.
The New Galaxy: Milkomeda
The new galaxy created from this collision has been nicknamed Milkomeda or Milkdromeda. Simulations suggest it will likely be a giant elliptical galaxy. This type of galaxy is usually shaped like a football or a sphere.
Over the next 150 billion years, the other smaller galaxies in our Local Group will also join this new Milkomeda galaxy. This will complete its evolution into a truly massive galaxy.
See Also
- NGC 2207 and IC 2163
- Mayall's Object
