The interactions of distant galaxies are fascinating to observe, especially as a massive collision between two galaxies can result in a process known as galactic cannibalism.
But while galactic cannibalism may sound like a scary and far-out notion from science fiction, it’s a very real process.
And one that might soon occur in some nearby galaxies. In fact, for us in the Milky Way, it might already be happening.
Galactic cannibalism is a fascinating subject, and one that can teach us plenty about the formation of the universe, and the future of our own galaxy.
Read on to find out what galactic cannibalism is, and why it’s so important.
What Is Galactic Cannibalism?
Galactic Cannibalism is a process in which two galaxies collide, and merge to become one larger galaxy.
It’s known as galactic cannibalism because one larger galaxy normally absorbs a smaller galaxy, causing the shape and orbits of the smaller galaxy to be lost in the merger.
What Happens When Two Galaxies Collide?
The thought of two galaxies colliding seems fairly unlikely. After all, there’s so much space in the universe.
But while the Milky Way is fairly isolated in this section of the cosmos, elsewhere, things can get pretty crowded.
Galaxies pass by in much closer proximity, which frequently leads to interactions.
The gravitational pull of these interacting galaxies might be mild, or it can lead to collisions between galaxies and an eventual galaxy merger.
Less extreme collisions are known as interactions. These typically occur between a larger galaxy and its satellite galaxies.
The satellite galaxy might attract the outreaches of the primary galaxies’ spiral arms, or their paths might interact and merge.
In some cases, two galaxies passing by will have enough momentum to keep on going.
They won’t fall into one another, but carry on traveling after the interaction.
However, sometimes the interaction will have a more long-lasting effect.
If galaxies collide and they lack momentum to move past, they can fall back into each other. This will cause the two galaxies to merge.
This most often creates an irregular galaxy, but can also result in an elliptical galaxy.
When a much larger galaxy collides with a smaller galaxy, this is galactic cannibalism.
The larger galaxy will look almost undisturbed, while the smaller galaxy will be torn apart.
The remains of the smaller galaxy will be distributed across the bigger cannibal galaxy. Within the galaxies, the changes can be intense.
The gravitational potential, which is the shape of the galaxy, will quickly alter, knocking stars into new orbits far removed from their previous cycle.
As a result, these merged galaxies are often full of stars moving in strange, even random, patterns.
In elliptical galaxies, which are often created by mergers, complex orbit networks dominate.
Interacting galaxies can also result in galaxy harassment. Galaxy harassment occurs between a bright galaxy and a low-luminosity galaxy.
When these two galaxies interact regularly, caused by high speeds and a high galactic density, the shape of both galaxies can distort.
The end result can transform spiral galaxies into dwarf spheroidals and dwarf ellipticals.
Why Is Galactic Cannibalism Important?
Understanding galactic cannibalism is important to understanding exactly how parts of the universe interact with each other.
It can also teach us more about the formation of galaxies, and how some have bulked up and grown throughout time.
By understanding this, we can learn more about the formation of the universe, as well as what the future has in store.
And for citizens of the Milky Way, there are some slightly more personal reasons for wanting to learn about galactic cannibalism.
Our galaxy might actually be undergoing galactic cannibalism right now.
The Large and Small Magellanic Clouds are two irregular dwarf galaxies that are orbiting the Milky Way.
However, they move quite fast and appear to be closer than ever before.
It’s theorized that this might be the beginnings of a collision, with our larger Milky Way galaxy drawing in the smaller Magellanic Clouds.
By observing the effects of galactic cannibalism, we have a better understanding of the future of our galaxy.
The Milky Way is eventually expected to collide with the Andromeda Galaxy and merge to form either a giant elliptical galaxy or a large lenticular galaxy.
This eventual collision is a long way off. In fact, it will take approximately 4.5 billion years for the two galaxies to meet.
The effects will first be observed in around 3.75 million years’ time when the tidal pull will cause both galaxies to distort.
After roughly 5 billion years, the two galaxies will have merged. And it might not be just the Andromeda Galaxy and the Milky Way merging.
The Triangulum Galaxy, the third-largest galaxy in the Local Group, might be involved as well.
It’s theorized that the Triangulum Galaxy may either orbit the merged remains of Andromeda and the Milky Way, to eventually be cannibalized as well.
Or it might collide with the Milky Way before the big event. It’s also possible that the Triangulum Galaxy is kicked out of the Local Group.
With so many possibilities, observing and understanding galactic cannibalism can help us better predict these results.
Although the term galactic cannibalism might sound dramatic, the actual process is a lot slower and steadier.
When the Milky Way and the Andromeda Galaxy collide, it’s unlikely to result in any stars or planets being destroyed.
Despite the fact that more than a trillion stars will be coming together, the gaps between these stars are too big to pose any real threat.
Galactic cannibalism can also teach us a lot about the formation of stars.
During a merger, thousands of stars can be created over the course of just a year.
Compare this to the Milky Way, which produces only around 2 stars every year.
During galactic cannibalism, these new stars are formed not by the collision of old stars, but by the merging of molecular clouds.
Have We Seen Galactic Cannibalism Happen?
Yes, we have been able to observe galactic cannibalism. One notable example involves the Mice Galaxies.
Located roughly 290 million light years away, the tidal force of these gravitational interactions has caused both galaxies to develop long tails, hence the name “Mice”.
They’re currently in the second phase of galactic collision.
Another example involves the Antennae Galaxies, which are in the third stage of galactic collision.
The galaxies began to approach each other 900 million years ago, and 600 million years ago were in a “passing through” stage, similar to that currently occurring in the Mice Galaxies.
Stars began to be released from the galaxies around 300 million years ago, leading to the antennae shape.
In another 400 million years, the two Antennae galaxies will be completely merged.
Actually observing galactic cannibalism is a tough process — it can take over a billion years for galaxies to collide, especially in our quieter part of the universe.
However, computer programs have been developed to accurately calculate exactly what happens when galaxies collide, and what that may mean for the fate of our own galaxy.
Galactic cannibalism is an intriguing phenomenon and one that is important to observe.
Not only does it teach us how the universe got to where it was today, it also teaches us what might happen to the universe in the future.
Perhaps even more importantly, by learning about galactic cannibalism, we learn about the potential future of our own galaxy.
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