June 13, 2013

What is a Black Hole?

Hi, I’m Emerald Robinson. In this “What Is” video we’re going to take a closer look at black holes.

A black hole is an area of space with extremely strong gravity–so strong that not even light can escape. Some black holes are tiny, while others have more mass than millions of suns. Some black holes are as old as the universe, while others are born when massive stars explode.

A stellar black hole develops with the death of a red supergiant, the most massive type of star. When smaller stars run out of helium fusion stops and the star dies. Fusion continues in red supergiants, with lighter elements fusing into heavier elements such as iron.

When the red supergiant runs out of elements to fuse, the star’s core collapses in a supernova. During the explosion even heavier elements form, including gold and uranium. After a supernova, if the star’s core has four or more times the mass of our sun, the remaining core collapses into a black hole with a densely packed mass equivalent to twenty suns. Our own sun is too small to end life as a black hole.

Tiny black holes also exist, some no larger than an atom. Despite their size, these small black holes can have an equivalent mass to a large mountain. Tiny black holes formed at the beginning of the universe.

Large galaxies, including our own Milky Way, have massive black holes at their centers. The Milky Way’s massive black hole is called Sagittarius A, and has a mass equal to four million suns packed into an area that would only hold a few million earth-sized planets.

Light cannot escape black holes, but astronomers can detect telltale radiation around the edges of a black hole. They can also spot a black hole if it affects nearby celestial objects. For instance, a black hole may siphon light and matter from a local star or nebula.

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