by Eventually, all galaxies, including our own Milky Way, will come to an end.
But how do galaxies die? If you want to destroy an entire galaxy, you have several options, depending on the level of destruction you want.
Related: Monster black holes may have murdered their host galaxies early in the universe
Option 1: Wake up the monster black hole
At the heart of almost every galaxy is a supermassive black hole. In the case of the Milky Way, we must Sagittarius A*, a beast weighing more than 4.5 million suns. Normally, these supermassive black holes are quiet and dormant, siphoning off any bits of gas or stars that pass too close. But from time to time, they feasted on a much larger meal. When they do, the gas swirls around them and compresses, reaching temperatures well over a billion degrees.
Those very high temperatures cause the gas to release a huge amount of radiation which then goes out to flood the whole. galaxy, heating any gas reserves and preventing the formation of new stars. Although things usually calm down afterwards, in the worst cases, the radiation from the vicinity of the black hole it can expel huge amounts of gas from the entire galaxy.
This doesn’t quite destroy a galaxy, but it effectively kills it by preventing new stars from forming for a long time and, in some cases, forever.
Option 2: Drop it into a cluster
Clusters of galaxies are the dense urban centers of the cosmos, typically home to a thousand or more galaxies. But there are more than just galaxies in these clusters; they also hold vast reservoirs of thin, hot gas called the interstellar medium (ICM).
The ICM is so thin that it would register as a vacuum in laboratories on Earth. But when galaxies fall into a cluster, they still have to swim through it. Initially, this results in a brief round of star formation as shock waves compress gas clouds throughout the galaxy. But eventually, the pressure from the gas does its work, picking up bits of gas from the galaxy like debris flying off a meteorite.
This leads to a cute situation called “jellyfish galaxies” called because the gas is stripped like the tentacles of a jellyfish.
Option 3: Put it in another galaxy
Galaxy collisions represent one of the largest releases of energy in the known universe, and that means it’s not a pretty sight. Our own Milky Way will collide with our neighborhood Andromeda galaxy in approx 5 billion years.
A slow and painful process lasting hundreds of millions of years, galaxy mergers can give rise to massive tidal tails that include streams of broken stars and gas that orbit the galaxies. During the collision and merger, large numbers of stars are lost through random interactions. And once the respective supermassive black holes merge, a fresh round of radiation propels the newly merged galaxy forward. The combined destruction depletes the galaxy of gas reservoirs, effectively halting star formation for good.
Option 4: Feed it to a much larger galaxy
If a smaller galaxy and a much larger companion merge, it can spell the end of the smaller galaxy. In fact, the European Space Agency has an application Gaia a survey found bones and bodies of cannibalized galaxies littered throughout the Milky Way.
One such example is called the Gaia sausages. This cluster of stars is distributed around the main properties of the Milky Way’s disk, such as an abundance of heavy elements and orbital parameters, which are different from the rest of the population. Astronomers think that the stars in the Gaia sausage are the broken remains of a small dwarf galaxy that was torn apart by its merger with the larger Milky Way.
Astronomers have identified numerous such accretions, streams, clumps and other remnants — a sign of the violent merger history of any reasonably sized galaxy such as our own.
Option 5: Wait still
Related stories:
—How do stars die?
—How many galaxies are there?
—Will our solar system survive the death of our sun?
Eventually, time will do its work. Galaxies are extremely stable; many of them have existed for over 10 billion years. But nothing lasts forever.
Far, far in the future, when the universe is much older than it is today, the Milky Way-Andromeda merger galaxy will begin to dissolve. It’s just gravitational chance. Most stars don’t spend most of their lives anywhere near each other, but occasionally, they wander too close. When they do, they do a little gravitational dance, sending them in new directions. Rarely, enough energy can be obtained to escape the entire galaxy.
This is extremely rare, but after trillions upon trillions of years, it is bound to happen. Eventually, everything in our galaxy will find its way into a supermassive black hole or disperse into the wider Universe. And that really is the end of our galaxy.
