Eventually, all galaxies, including our own Milky Way, will meet their end.
But how do galaxies die? If you’re in the mood to destroy an entire galaxy, you have several options depending on your desired level of destructiveness.
Connected: Monster black holes may have killed their host galaxies in the early universe
Option 1: Wake up the monstrous black hole
At the heart of almost every galaxy sits a supermassive black hole. In the case of the Milky Way, we have Sagittarius A*, a beast weighing more than 4.5 million suns. Normally, these giant black holes are quiet and dormant, just gobbling up any particles of gas or stars that wander too close. But sometimes they feast on a much larger meal. When they do, this gas swirls around them and compresses, reaching temperatures in excess of a billion degrees.
These absurdly high temperatures cause the gas to emit a huge amount of radiation, which then escapes to flood the whole galaxy, heating up all the gas supplies and preventing new stars from forming. While things usually calm down after that, in the worst cases radiation from the surroundings of Black hole it can outright eject massive amounts of gas from the galaxy as a whole.
This doesn’t completely destroy a galaxy, but it effectively kills it by preventing new stars from forming for a very long time, and in some cases forever.
Option 2: Drop it into a cluster
Galaxy clusters are the dense urban centers of space, typically home to a thousand or more galaxies. But these clusters contain more than galaxies; they also possess vast reservoirs of hot, thin gas known as the intracluster 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 leads to a short cycle of star formation as shock waves compress gas clouds throughout the galaxy. But eventually the pressure from the gas does its job, detaching chunks of gas from the galaxy like flying debris from a meteorite.
This leads to a sweet situation known as “jellyfish galaxies“, so named because the ejected gas resembles the tentacles of a jellyfish. Although most galaxies survive their descent into the cluster’s ICM, some smaller galaxies evaporate completely.
Option 3: Smash it in another galaxy
Galaxy collisions represent one of the largest releases of energy in the known universe, and that means it’s not exactly a pretty sight. Our own Milky Way will collide with the neighboring one Andromeda galaxy in approx 5 billion years.
A slow and torturous process lasting hundreds of millions of years, the merging of galaxies can produce huge tidal tails, which consist of streams of broken stars and gas that curl around the galaxies. During the collision and merger, countless stars are lost through random interactions. And once the respective supermassive black holes meet, a new round of radiation hits the newly merged galaxy. The combined devastation depletes the galaxy of gas reservoirs, effectively halting star formation forever.
Option 4: Feed it a much larger galaxy
If a smaller galaxy and a much larger companion merge, it could spell the end of the smaller galaxy. The European Space Agency actually Gaia research found bones and corpses of cannibalized galaxies scattered throughout the Milky Way.
One such example is known as Gaia sausage. This collection of stars scattered throughout the Milky Way’s core share properties, such as abundances of heavy elements and orbital parameters, that differ from the rest of the population. Astronomers believe that the stars in the Gaia sausage are the tattered remains of a small dwarf galaxy that was torn apart by its merger with the larger Milky Way.
Astronomers have identified dozens of other such collections, streams, clumps and remnants – a sign of the violent merger history of any decent-sized galaxy like ours.
Option 5: Just wait
Eventually, time will take its toll. Galaxies are remarkably stable; many of them have been around for more than 10 billion years. But nothing is forever.
Far, far into the future, when the universe is many times older than it is today, the Milky Way-Andromeda galaxy merger will begin to disintegrate. It’s just a matter of gravitational chance. Most stars spend most of their lives close together, but sometimes they wander too close. When they do, they perform a little gravitational dance, sending them off in new directions. It is very rare that a person can get enough energy to escape the galaxy completely.
It’s incredibly rare, but after trillions and trillions of years it’s bound to happen. Eventually, everything in our galaxy will either find its way into a giant black hole or be dispersed into the wider universe. And this will indeed be the end of our galaxy.
