Accretion. In short, accretion means growth by accumulation.
Land on Earth can form from accretion of soil deposited by rivers or sea.
Planetary bodies can also grow from accretion as gravitational forces
attract debris and other matter.
But we want to talk about accretion in astronomy.
Accretion is one way we can see black holes.
Black holes have intense gravitational mass,
pulling in everything in the vicinity, including light.
Without that light, we can't see black holes, but we can see
the disk-shaped flow of gas and dust that forms around some black holes.
We call these accretion disks, and they can form around
black holes of any size, as well as around some stars.
Material in black hole accretion disks is really hot, like millions of degrees.
This is caused by the collision
of particles in the accretion disk as they are pulled into their black hole.
These collisions can cause accretion disks to release X-rays,
which can allow us to locate some black holes.