A black hole is a region of spacetime where the gravitational pull is so strong that nothing, not even light, can escape. They form when very massive stars collapse at the end of their life cycles, with the smallest being stellar mass black holes comparable to several Suns, and the largest being supermassive black holes millions of times more massive than the Sun located at the center of galaxies. Black holes are extremely dense objects that can vary dramatically in size, from being only slightly larger than an atom to containing as much mass as millions of Suns.

1. BLACK HOLE

2. What is a black hole ?
O A black hole is a region of spacetime from
which nothing can escape, even light.
O Black holes are not really holes at all.
They are the opposite of empty! Black
holes have the most matter stuffed into
the least space of any objects in the
universe. Because they are so compact,
they have very strong gravity.

3. Two types of black hole

4. Stellar mass black hole
O - This type of black hole forms when a big
star burns up all its fuel and explodes
(called a supernova). Then what's left
collapses into a super-compact object—a
black hole. Stars must contain quite a bit
more matter than our Sun for this to
happen. So our Sun, and most stars, will
never become black holes.

5. Supermassive black hole
O You can think of this type as a "million-big-
star" black hole, because it contains as
much matter as one million to 100 million
Suns! Astronomers think that
supermassive black holes are lurking at
the centers of galaxies, including our own
Milky Way galaxy. They don't know yet
how these humongous black holes are
formed.

6. How Do Black Holes
Form?
Scientists think the smallest black holes formed
when the universe began.
Stellar black holes are made when the center of a
very big star falls in upon itself, or collapses. When
this happens, it causes a supernova. A supernova is
an exploding star that blasts part of the star into
space.
Scientists think supermassive black holes were made
at the same time as the galaxy they are in.

7. How Big Are Black
Holes?
Black holes can be big or small. Scientists think the smallest black holes are as small as
just one atom. These black holes are very tiny but have the mass of a large mountain.
Mass is the amount of matter, or "stuff," in an object.
Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the
mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy.
Earth's galaxy is called the Milky Way.
An artist's drawing shows the current view of the Milky Way galaxy. Scientific evidence
shows that in the middle of the Milky Way is a supermassive black hole.
The largest black holes are called "supermassive." These black holes have masses that are
more than 1 million suns together. Scientists have found proof that every large galaxy
contains a supermassive black hole at its center. The supermassive black hole at the center
of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns
and would fit inside a very large ball that could hold a few million Earths.