Episode #7 of the course “Strangest Things in Space”
Galactic cannibalism is the collision of two galaxies and the subsequent absorption of parts of one into the other. The closest galaxy to us, Andromeda, is over 2.5 million light years away. But in many corners of the universe, galaxies are much more tightly packed in. All galaxies move, too. With many massive moving bodies swirling around, it’s only a matter of time before they collide and “eat” each other.
When galaxies collide, their individual gravitational forces reach out and pull the other in. You can picture a massive “gravity arm” reaching out and grabbing a chunk of the other galaxy. Except this is a two-way event. However, the larger galaxy—the one with the greater gravitational pull—almost always wins the fight and causes more distortion to the smaller galaxy.
Galactic cannibalism doesn’t just distort galaxies, though—it births new stars. A major component of galaxies are clouds. When galactic clouds collide, stars are born.
We can look at our own solar system, the Milky Way, to get an example of this. The Milky Way is comprised of two parts: a disk and a halo. Most of the stars in the disk are relatively young and were likely formed in the Milky Way itself. The stars in the halo, on the other hand, are much older, more ancient stars. Most scientists believe that these ancient halo stars were formed in neighboring systems or galaxies but were sucked into the Milky Way due to its larger gravitational pull.
Understanding galactic cannibalism helps to answer questions about our own solar system as well, particularly about whether our solar system is ordinary or unique. By understanding that, we could gain more insight into the possibility of another planet like Earth.
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