Galaxies are mind-bendingly big structures, but one recently discovered galaxy is an absolute colossus stretching millions of light years across despite having less mass than many of its counterparts.
The galaxy in question, Alcyoneus, is a special type of galaxy known as a radio galaxy, defined by a unique feature of its central supermassive black hole.
When any black hole gobbles up material, it does so similar to water swirling down a drain. As water gets closer to the drain, its angular velocity increases considerably.
The same happens to matter as it swirls around a black hole’s event horizon, though the velocity of matter just outside the event horizon can approach significant fractions of the speed of light.
And, sometimes, some of that matter is able to escape being eaten by riding the immense magnetic field of the black hole to the magnetic poles and getting shot out into space as relativistic jets of highly charged particles.
These jets can travel hundreds of thousands of light years before forming into massive lobes. These lobes interact with the intergalactic medium to generate radio emissions, giving this type of galaxy its name.
With Alcyoneus, though, these lobes are absolutely gigantic, extending five megaparsecs from the end of one to the end of the other, which translates to about 16.3 million light years across.