What is a black hole?
A black hole is a region of space whose gravity is so strong that it acts like a giant vacuum cleaner in space. Anything that gets too close gets sucked in. When it hits the center, the singularity, it disappears forever. The gravity in black holes is SO strong that it tugs at space and time, slowing down time and stretching out space. Not even light, the fastest thing in the universe, can escape from a black hole.
Wouldn't a black hole swallow up everything in the universe?
No. The boundary of a black hole is called the "event horizon," and it has a limited extent. The gravity of a black hole is the same as a normal object, except that it's usually a lot because most black holes are very dense. As long as you're outside the event horizon, you can avoid getting sucked in. If you're inside the event horizon, however, you're doomed.
How are black holes created?
For most of their lives, stars remain the same size because they have a balance of forces: heat made by burning fuel pushes the star out, and the effect of gravity pulls it in. After billions of years, when the star has used up all of its fuel, it collapses under its own weight. Two scientists, Oppenheimer and Snyder, proved that if the start has more than 3.2 times the mass of the Sun (known as 3.2 solar masses), there is nothing to stop it from collapsing into a black hole.
Can only stars become black holes, or could planets and other things become black holes? If not, why is this?
Technically, anything can form a black hole, whether it be a star, a planet, or a human being! In order for something to become a black hole, it has to be compressed so that it's smaller than its Schwarzschild radius. The Schwarzschild radius is a distance from the center of a star or another object where math goes crazy (once an object become a black hole, the Schwarzschild radius can be called its "event horizon." At this distance, space becomes infinite, and time disappears. Mathematicians call this "singular" (this is where the word "singularity" came from). Most of the time, this Schwarzschild radius is much smaller than the object. The Schwarzschild radius of the Sun is three kilometers. The formula for finding something's Schwarzschild radius is as follows:
R* = 1.48×10-27 M
where R* is the Schwarzschild radius in meters and M is the mass of the object in kilograms.
(NOTE: 1.48×10-27 is using scientific notation, and really means 0.000000000000000000000000
Realistically, however, only stars naturally form black holes, and only stars that have more than 3.2 times the mass of our Sun. Only through some strange supernatural or alien force could you or me become a black hole, because we just don't have enough mass.
How do we know that black holes exist?
Until recently, black holes were just theories and speculations. However, on February 27, 1994, the Hubble Space Telescope discovered what seemingly had to be a black hole. There wasn't any other explanation for it. Other black hole candidates had been found before, but none that couldn't be explained otherwise, as was the case with this 3-billion-solar-mass black hole at the center of M87.
Are we in any danger of falling into a black hole?
No. Although it is believed there is a super-massive black hole at the center of our galaxy, we are on the outside of our galaxy, on one of the spiral arms, quite far from the massive monster.
Adapted from the Internat