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An artist's drawing shows a
large black hole pulling gas
away from a nearby star. Image
Credit: NASA E/PO, Sonoma
State University, Aurore
Simonnet
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.
Image Credit:
NASA/JPL-Caltech
What Is a Black Hole?

A black hole is a place in space where gravity pulls so much that
even light can not get out. The gravity is so strong because
matter has been squeezed into a tiny space. This can happen
when a star is dying.

Because no light can get out, people can't see black holes. They
are invisible. Space telescopes with special tools can help find
black holes. The special tools can see how stars that are very
close to black holes act differently than other stars.


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.

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.


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.


If Black Holes Are "Black," How Do Scientists Know They Are
There?

A black hole can not be seen because strong gravity pulls all of
the light into the middle of the black hole. But scientists can see
how the strong gravity affects the stars and gas around the
black hole. Scientists can study stars to find out if they are flying
around, or orbiting, a black hole.

When a black hole and a star are close together, high-energy
light is made. This kind of light can not be seen with human eyes.
Scientists use satellites and telescopes in space to see the
high-energy light.


Could a Black Hole Destroy Earth?

Black holes do not go around in space eating stars, moons and
planets. Earth will not fall into a black hole because no black hole
is close enough to the solar system for Earth to do that.

Even if a black hole the same mass as the sun were to take the
place of the sun, Earth still would not fall in. The black hole would
have the same gravity as the sun. Earth and the other planets
would orbit the black hole as they orbit the sun now.

The sun will never turn into a black hole. The sun is not a big
enough star to make a black hole.


How Is NASA Studying Black Holes?

NASA is using satellites and telescopes that are traveling in
space to learn more about black holes. These spacecraft help
scientists answer questions about the universe.


SOURCE Heather R. Smith/NASA Educational Technology
Services NASA
This image of the center of the Milky Way galaxy was taken by the Chandra X-ray
Observatory. Image Credit: NASA/CXC/MIT/F.K. Baganoff et al.
This artist's drawing shows a
supermassive black hole in the
center of a galaxy. The black hole
is surrounded by a cloud of
material that is spiraling into it.
Image Credit: NASA E/PO, Sonoma
State University, Aurore Simonnet
"Victoria crater" Image Credit: NASA/JPL/Cornell  SPACE