A Hole in the Sky

One of the strangest objects in the sky is one we can never hope to see, no matter how large our telescopes are: a black hole. Forever dark, a black hole is a region of space where the gravity is so intense that even light can never escape. But our eyes are not the only way we " see" things. More important than our eyes, we see with our minds.

All it takes to make a black hole is to take a very massive object, like the earth or a star, and make it very small. If we could, with a magic wand, make the earth a quarter as big as it now is now, keeping all its mass, we would weigh twice as much as we do now and it would be harder for us to walk, much less launch space ships. And if, with the same magic wand, we squashed the earth to the size of a marble, we would weigh trillions of times as much, and not even light could escape the earth. It would be a black hole.

Well, there is such a magic wand. It's called gravity. At the end of a star's life, the nuclear fires in its core flicker and die out. For billions of years these nuclear fires have been pushing outwards and keeping the force of gravity at bay. Now gravity takes over and the star begins to collapse. If the star is very large, much larger than the sun, nothing can halt its complete collapse. The entire star, now smaller than the head of a pin, becomes a black hole.

Overhead tonight is Cygnus the swan, which we know as the Northern Cross. In Cygnus, there is a dim star that wobbles. We don't see anything that could cause this wobble, such as a companion star , but we know there's something there, something very massive. When we point our powerful X-ray telescopes in that direction, they detect a powerful beam of X-rays coming from this invisible companion. And this beam flickers hundreds of times a second. That means that the object is very small, no more than a few hundred miles across. Scientists think that gasses spiraling in to this object from the star they see are heated to such high temperatures that they emit X-rays. This object is called Cygnus X-1. It's very small and very massive. It may what wešre looking for: a black hole.

(07/12/06)