Black, Black Holes

4/15/07 – 4/21/07
by C. Zaitz

One of the strangest, most compelling objects in the universe are black holes. The idea that something can be so powerful, so destructive, and yet invisible to us is very compelling. Ever since they were first speculated to exist, we have been searching the skies for the invisible monsters, the star-eating, gas-sucking anomalies of nature.

At first, it was very hard to find black holes. You have to get creative; you have to find something that the black hole is affecting. It’s like looking for the skunk that gets into your garbage every night. You can’t see it; it’s dark and you’re looking in the night, but skunks certainly leave clues behind. So we try to “sniff out” black holes, and look for the destruction they cause.

One of the best indicators of the presence of a black hole is a binary star system that emits X-rays. Binary star systems are quite common in the galaxy, and it turns out that often, one star is much bigger than the other. Big stars, like Elvis, tend to burn very brightly and burn out quickly. When massive stars die, they often become black holes. The companion star still orbits the “hole” left behind, but if material from the companion star happens to get too close to the black hole, it will get swirled in and “eaten,” streaming out X-rays as tidal forces ionize the infalling gas. We see the X-rays, and can begin to pinpoint the black hole.

There are different sizes of black holes, but the most familiar are the ones that come from big stars, like the star in the shoulder of Orion called Betelgeuse (commonly pronounced “beetle-juice” to the delight of untold numbers of elementary students.) Betelgeuse is said to be bigger than the orbit of Mars. When such a massive star dies, it generally ends up in one of the most spectacular events in the universe, a supernova explosion. Most of the mass of the star is violently distributed into space as giant clouds of hot, colorful gas. But the core of the star remains, is still very massive, and has no means to keep it from collapsing. It begins a journey that no force in nature can hinder, and it only stops until all that once was the star is found in one single point - the singularity.

One curious thing about black holes is their affinity for infinity. Laws of physics, as we know them, start to get wobbly when we get close to the “singularity.” This is the point at which what used to be matter has collapsed to a single point. This is very hard to imagine. How can a lot of stuff, with a lot of mass and gravity, collapse into a single point? And how big is that point?

Einstein’s theory of general relativity tells us that at the singularity, all the core’s mass is compressed into a space with zero volume, while its density and gravity are infinitely big! But quantum physics, with its uncertainly principle, says more reasonably that it’s a very large amount of matter squeezed into the smallest possible amount of space. Still, it’s a pretty quirky concept. Perhaps that’s why they are so very interesting.

Next week, we will talk about the even more curious super-massive black holes. Meanwhile, enjoy lovely Venus in the sunset and Saturn crossing the southern skies all night long.

Until next week, my friends, enjoy the view.