Black Holes: The Other Side of Infinity
The universe is filled with violence beyond comprehension, forces that can shred the very structure of space-time -- the mysterious black holes.
Black holes are so dense that light cannot escape from them, and they are difficult to detect. Satellites above the Earth's atmosphere can detect bursts of high energy radiation given off by black holes. Dozens of stellar black holes have already been detected in the Milky Way, where there may be tens of millions more.
We think of stars as being like our sun, one star of one hundred fifty billion in the Milky Way, which is one galaxy of hundreds of billions that fill the universe. Large stars burn their hydrogen fuel faster than sun-like stars, and as the fuel supply runs low, gravity begins squeezing their cores, starting new reactions in successively deeper shells. As an iron core grows beyond a maximum limit, the core collapses, and a shock wave rips the outer layers away in a supernova explosion. At the core, gravity becomes so strong that light cannot escape.
Gravity is the warp in space-time caused by massive objects, described by equations developed by Albert Einstein. But how warped can space-time get? In an extreme case, a red-giant star with a million times the mass of Earth collapses into a space one million times smaller than the Earth.
Entering the warped space, you find the pull of gravity becoming stronger and stronger as you get nearer to the mass concentration at the center. Finally, you reach the point of no return, the event horizon.
Another type of black hole exists near the center of most galaxies, the super-massive black hole around which the galaxy's stars revolve. One of the biggest is a four-million solar mass black hole at the center of the large galaxy M87. Where do these super-massive galaxies come from?
To find out, the events surrounding the birth of the universe in a Big Bang were modeled in super computer simulations. The model tells us that a few hundred million years after the Big Bang, the gases of the cooling universe began to be drawn together by gravity. Clouds grew and heated at their cores, forming the first massive stars. These stars died in supernova explosions that littered the early universe with large black holes.
A space probe named SWIFT looks across space and back in time to see these early stars flaring in supernova explosions. The black holes grew larger, swallowing stars and clouds of gas as they migrated to the centers of their young galaxies. Others grew as galaxies merged, and the black holes at their cores combined into larger black holes.
Astronomers have searched for the black hole at the core of the Milky Way galaxy. We are located about two-thirds of the way from the center to the outer edge of the Milky Way. Stars and clouds of dust and gas hide the core from our vision, but instruments can detect radiation that we cannot see. As you get closer to the center of the Milky Way, the density of stars increases in an area called the central bulge. Closer to the center are gas remnants of past supernovas and swirling clouds of gas. Very close to the center, stars whiz around an unseen mass.
Using computer simulations, we can see what it would be like to enter the black hole. Surrounding the hole is a disk of gas falling toward the center, but the inward falling gas collides with itself, and a large part is pushed away, forming jets racing outward.
Nearing the event horizon (the point beyond which anything that crosses cannot escape), space is warped, and it behaves like a lens. Falling below the event horizon, we see a storm of energy and matter continuing to fall towards the center of the black hole, where there exists a point called a singularity -- or a point of infinite density. An eye at the center of the storm may be an entrance to a wormhole, a passage for matter that emerges from a white hole at the other end. A white hole may be a gateway into another universe.