Just the name sounds monstrous: Black-hole. The related mathematics and terminology behind concepts like a Schwarzchild Radius, the Kerr Solution, or an Einstein-Rosen Bridge, are usually enough to spook all but the most determined layperson into full intellectual retreat. But the basics of a black-hole don't require advanced math or counter-intuitive physics to appreciate. The fundamental force that creates them is one we all know well. Even more exciting, in the near future, black holes may be transformed by technology from distant, inaccessible objects embedded deep in space and time, to laboratory curiosities right here on earth, and some say we'll be able to use them to make baby universes as well!
NPR -- Is this a joke? No, say a bunch of physicists. ... One day it may be possible to go into a laboratory on Earth, create a "seed" -- a device that could grow into a universe -- and then there would have to be a way to get that seed, on command, to safely expand into a separate, infinite, unexplorable but very real alternate universe.
A black-hole is any physical object which has been compressed into a volume so small, that the escape velocity from its surface exceeds the speed of light. If the compressed version is a sphere, then for any mass, there will exist a defined radius which would render it a black hole. For an object as massive as the earth, this radius works out to just under half an inch. For the sun, it would be around two miles. In physics, this critical dimension is known as the Schwazchild Radius. You can calculate the SR for any mass -- including your own body -- here.
A round fired from a cannon on the surface of earth eventually falls back, unless it is fired with enough velocity to overcome earth's gravity. The more massive the planet, the higher the gravity, and the greater the escape velocity will be. Black holes are so dense and massive that the escape velocity exceeds the speed of light, even photons fall back, just like the cannon ball on the right. Illustration by Karen Wehrstein
From outside, such an object would appear perfectly black, because no light can escape, and that's why it's called a black-hole. Of course, if all light is trapped, inside, it could be lit up brighter than a supernova.
One way black holes can form, we think, is when a massive star convulses and dies leaving behind a super dense core that implodes. Large stars burn out fast. Under the right conditions, a typical large galaxy can produce billions of blue-white super-giant stars in just a few million years, ultimately leaving huge numbers of steller mass black holes behind. Since there are more stars in the center of the galaxy, it's not surprising that that's where left over stellar mass black holes might merge to form a single, successively larger, supermassive black hole. Although there is some debate as to which came first: the super-massive black hole or the galaxy.
Left: Lobes of hot matter stretching for tens of thousands of light-years from the core of the elliptical galaxy NGC 4261, shown in radio wavelengths. Right: The core of NGC 4261 is this accretion disk several hundred light years in diameter swirling around what is thought to be a titanic black hole.
But there is growing speculation that tiny, submicroscopic black holes may exist, or may have once existed. Even more bizarre, some astronomers wonder if our entire universe could have grown from such an exotic seed, weighing in at only a few kilograms!
Cosmologists now theorize that the total energy of our entire universe might be zero, after we add up the positive contributions from matter and dark energy to the negative contribution of gravity. That means if we create just the right conditions in the lab, we can create a completely new universe basically out of nothing. It's simply a matter of balancing the cosmic books!
Incredibly, we may be able to produce the black holes soon. Starting around 2008, the Large Hadron Collider is expected to be up and running, and it might be able to create very, very tiny black holes. It's unclear to say the least how to impregnate a mini-black hole with this evolving negative and positive energy tug of war. But who knows, one day, in the not too distant future, we may be able to create baby universes. And thank heaven for little universes, for little universes get bigger every day ...