What is a black hole?

On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as seen in this image that spans some 700 light years across. An artist's illustration on the right depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. New studies with data from Chandra and several other telescopes have determined the black hole's spin, mass, and distance with unprecedented accuracy.

Black holes are places in space where even light cannot escape due to their high gravitational force. The reason for the very high force of gravity in a black hole is that matter is compressed inside a small space. This can happen when a star is dying.

Because no light can get out of the black hole, people cannot see the black holes. They are invisible, but space telescopes with special tools can find black holes. These special tools can record the different behavior of stars that are very close to the black hole compared to other stars.

How big are black holes?

Black holes can be large or small. Scientists believe that the smallest black holes are the size of a single atom. These black holes are very small but have a mass the size of a large mountain. Mass is the quantity of measuring the amount of matter in an object.

On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as seen in this image that spans some 700 light years across. An artist’s illustration on the right depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. New studies with data from Chandra and several other telescopes have determined the black hole’s spin, mass, and distance with unprecedented accuracy.

An artist’s painting of a black hole called Cygnus X-1. This black hole formed when a large star collapsed. This black hole draws matter in from the blue star.

There is another type of black hole called a stellar black hole. Its mass can be 20 times greater than the mass of the sun. There may be many of these stellar black holes in the galaxy in which the Earth is located. The name of the galaxy in which the earth is located is the Milky Way.

The largest black holes are called supermassive black holes. These black holes have a mass greater than the mass of a million suns next to each other. Scientists have proven that every large galaxy has a large mass black hole at its center. The supermassive black hole at the center of the Milky Way is called Sagittarius A. This black hole has a mass of 4 million suns and can be placed inside a large ball about the size of millions of planets.

How are black holes formed?

Scientists believe that the smallest black holes formed when the universe began.

A painting by an artist showing the current view of the Milky Way. There is evidence that there is a large black hole at the center of the Milky Way galaxy.

Stellar black holes form when the center of a very large star is destroyed within itself, called a collapse. When this happens, it creates a supernova or supernova. A supernova is an exploding star that throws part of a star into space.

Scientists think the supermassive black holes formed at the same time as the galaxy in which they are located.

If black holes are not visible, how do scientists know they exist?

Black holes are not visible because intense gravity pulls all light to the center of the black hole. But scientists can see the effect of extreme gravity on stars and gases around the black hole. They can study stars to see if they are near a black hole.

Image of the center of the Milky Way by the Chandra X-ray Observatory. Taken.

When a black hole and a star are placed close to each other, high-energy light rays are produced. This type of light is not visible to the human eye. Scientists use satellites and space telescopes to see these energetic rays.

Can a black hole destroy the earth?

Black holes do not move in space to devour stars, moons and planets. The Earth does not fall into a black hole because no black hole is close enough to the solar system for this to happen to Earth.

Sagittarius A is a black hole at the center of the Milky Way.

Even if a black hole with a mass the size of the sun could replace the sun, the earth would not fall into it. This is because the black hole had a gravity equivalent to the current gravity of the sun, and the earth and other planets in the solar system moved around the black hole in the same way as they do now in orbit around the sun.

Of course, the sun will never turn into a black hole because the star sun is not big enough to form a black hole.

How does NASA detect black holes?

NASA is using satellites and telescopes moving in space to further study black holes. These spacecraft help scientists answer fundamental questions about the universe.