When Stars Go Boom

Narrator (April Hobart, CXC): Our Sun is a star. In fact, it is the closest star we'll ever see. The Sun is about 5 billion years old and will live for about 5 billion more. But not all stars live this long. Some really big stars – those that are about ten or twenty times bigger than the Sun --- live for only a few million years. Our Sun is too small to explode, but when these big stars run out of fuel, they go out with a bang!

What happens at the end of a big star's life? It has to do with how stars, which are essentially big balls of gas, shine. A star's energy is the result of gravity, which pulls all of its matter toward the center. This compresses the center of star and makes it so hot there that matter undergoes a process called nuclear fusion. Fusion is when atoms collide. When this happens, energy is released. This is what holds up the outside of the star against gravity. But when the center runs out of fuel, the outer layers come crashing down. A star like the Sun will get crushed down to the size of Earth when this process happens to it billions of years from now. For stars much larger than the Sun that we've talked about, they don't go so quietly. Instead when their outer layers collapse, it generates a massive explosion that astronomers call a supernova. These supernova explosions blow the star apart and, for several days, generate more light than a billion stars.

Astronomers think that a supernova explodes about once every 50 years or so somewhere in our Galaxy. About 25 years ago, a star did explode as a supernova and astronomers were able to witness it almost as it happened. In February 1987, a young scientist was working at a telescope in Chile. He noticed that there was a bright object in the images of the sky that had never been there before. He knew he had discovered a supernova. Today, this object is known as Supernova 1987A. Astronomers using all different kinds of telescopes – both on the ground and in space – have been watching ever since. Pictures from the Hubble Space Telescope show rings of matter that were thrown out 20,000 years before the star exploded. The Chandra X-ray Observatory images reveal the explosion now reaching the inner ring, making it so hot that it glows in X-rays.

Astronomers also study supernovas that have exploded in the past. For example, Chinese astronomers recorded the sudden appearance of a star almost a thousand years ago in the year 1054. Today, we call this object the Crab Nebula. What would have appeared as a bright star nearly a millennium ago is a spectacular dynamic object when scientists use modern telescopes like Chandra to study it.

Supernova 1987A and the Crab Nebula are just two examples of the many explosions that astronomers use to learn about what happens when stars go boom. Remember, even though we don't see obvious changes in stars on timescales of days or even years, they are changing. Stars don't last forever, and supernova explosions are some of the most exciting ways for stars to end their lives.