Black Holes Get an Identity Check ; Scientists Now Say There's Overwhelming Evidence That They Do Exist

Article excerpt

Astronomers are scientists of faith. How else could they believe in such an incredible thing as a black hole? It's an object that has collapsed to such density nothing escapes its strong gravity. Astronomers can't see it. They have no direct evidence that it exists. Yet their faith now is so strong it's reshaping their views of how galaxies form, how energy flows through the cosmos, perhaps even how our universe was born.

Einstein hated the concept, even though his theory of general relativity predicts it. Kip Thorne loves it. The California Institute of Technology astrophysicist says "we have close to a 100 percent case that [collapsing objects] leave black holes."

Cornell University theorist Eanna Flanagan nudges even closer to certainty, saying "I'm 100 percent convinced personally." They expressed their confidence during a presentation organized by Cornell's Astronomy Department in Ithaca, N.Y., last month.

Until a few years ago, even such true believers wouldn't have been that confident. New circumstantial evidence encourages many astronomers to consider the reality of black holes beyond reasonable doubt.

Some of that evidence is illustrated here. A reputed black hole at the heart of a nearby galaxy shoots a high-speed jet thousands of light years across space. A black hole feeding hungrily in another galaxy burps out a bubble of hot gas that is too much to swallow. Studies of how galaxies and black holes age suggest an intimate relationship.

To understand why such things excite astronomers requires a nodding acquaintance with some of the mind-bending notions the theory of space-bending black holes entails. Black holes can be as small as several solar masses or as gigantic as the billion-solar- mass black holes at the core of many galaxies. Massive or not, there's no matter in the structure of a black hole. As Dr. Thorne explains, "A black hole is made wholly and entirely solely by the warpage of space and time."

There is no gravitational force in general relativity. The gravity of a mass manifests itself in this warpage. Nothing escapes a black hole because, at its perimeter, space is so strongly curved that all paths lead into the hole. Thorne prefers to think in terms of time. He explains that time flows inward at the edge of a black hole. Nothing can escape because the future of everything on the perimeter lies inside the hole.

If that sounds weird, consider what happens just outside the perimeter. Matter under a black hole's influence orbits just as planets orbit a star. That matter can also spiral down and be swallowed up. But near the hole itself, it's not just matter swirling around. A rotating black hole drags space itself around with it, carrying along any matter in that space. Thorne describes this as "a motion of space around a black hole in a way that's similar to the winds around a tornado." He adds that space around a black hole not only spins around, it slides into the black hole. Some space slides inward at light speed as seen from the outside.

There's enormous energy involved. Thorne says the space vortex energy represents 29 percent of the black hole's mass. He notes that a black hole is many times more efficient at turning mass into energy than are nuclear processes.

Not everything caught in a black-hole dance is sucked inside. The system has to get rid of excess matter and rotational momentum. Magnetic forces in the swirling dust and gas circling the hole escape in powerful jets and outflowing bubbles. The interaction of such material with itself and with interstellar or intergalactic gas generates X-rays, gamma rays, radio waves, and sometimes spectacular light shows.

The Hubble Space Telescope and other orbiting observatories give astronomers a front-row seat. …