Black holes are very dense amounts of matter that are made of the remnants of a large star much more massive than the sun after a supernova explosion. The gravitational field of a black hole is so strong that nothing can escape the perpetual void; not even the speed of light is able to escape the gravitational field of a black hole.

Nasa's online website holds a lot of information for black holes. Some of which will be told here. Feel free to check out their website to find much more information.

Current technology makes it impossible to observe black holes directly regardless of what they can detect (e.g. light or x-rays). However; it is possible to make conclusive judgments about the presence and locations of black holes by studying the effect of matter around them. We're a black hole to pass through a galactic neighborhood full of matter, a process known as accretion would cause that matter to move inward towards the black hole.

Black holes typically form after a large star reaches the end of its life cycle and causes a supernova explosion. Smaller stars usually don’t have enough mass to become a black hole and form to become a dimly lit neutron star instead.

The event horizon is the point of no return for anything slower than the speed of light. If a living organism were to cross the event horizon, how long they live depends on the overall mass of the black hole. A larger black hole would allow the organism to live longer while falling into a smaller black hole is likely to lead to an instantaneous death. Essentially the further you are from the singularity, the longer you have to experience a black hole.

The “hole” part of the black hole is currently called the singularity, except no one exactly knows what it is; meaning it could be infinitely dense and concentrated into a single point in space without any surface or volume or not, either way, no one has a definitive answer.

Furthermore, a huge mystery that has been recently brought up by astronomers relates to the radical differences in sizes of black holes in the universe. On one end, there are countless black holes that have formed from the remnants of stars much more massive than the sun that have exploded into supernovas and collapse into a black hole. These black holes can measure anywhere between ten to 24 times more massive than the sun. They are visible when matter moves close to the black hole and sort of distorts over the imaginary line called the event horizon. Based on how many presently discovered stars however, there are estimated to be potentially nearly a billion black holes in the Milky Way alone.

On the other end of the spectrum, we have giant black holes that are called “supermassive” black holes. Supermassive black holes are believed to be at the center of all large galaxies, including the Milky Way and are billions of times more massive than the sun.

Hawking radiation is the radiation that is given off during a black holes life. It was named after the physicist Stephen Hawking in 1974. Hawking Radiation is sort of similar to empty space; however, empty space is not technically empty as it has particles that instantaneously pop into existence and annihilates each other. When this occurs on the event horizon of a black hole, one of the particles retreats into space and the other rushes into the black hole towards the singularity. This process begins slowly, but over the course of the black holes life, this process begins to speed up until it becomes sufficiently smaller. When a black hole becomes approximately the mass of a small asteroid it radiates at approximately room temperature and begins to heat up at it shrinks further via Hawking Radiation. When the black hole dies in its final seconds it explodes with the energy of billions of nuclear bombs. However, this takes extremely long to occur and by the time the final black hole dissipates the universe will have become sterile and inhabitable long before that even happens.