For the first time, scientists believe they have witnessed the birth of a black hole.

The evidence began arriving 30 years ago from a star 50 million light-years away that had imploded, setting into motion events that created a region where gravity is so great that nothing can escape, even light.

The initial 1979 observation of the exploding star was made by an amateur astronomer from Western Maryland, but the profession's top scientists have studied it intently with increasingly sophisticated orbiting X-ray telescopes.

In announcing the discovery Monday at NASA headquarters, the researchers said that although the information they have collected is consistent with the birth of a baby black hole, they cannot rule out other possibilities. Nonetheless, they spoke enthusiastically about what they are learning and will learn about the evolution of black holes.

"We've never known before the exact birthday of a black hole, and now we can watch as it grows into a child and teenager," said Kimberly Weaver, an astrophysicist at NASA's Goddard Space Flight Center. "Learning about black holes has been like solving a puzzle, and this will help us get closer to a full understanding."

The researchers said that what they think is a black hole is about five times the mass of our sun and was formed from the explosion of a star about 20 times as massive as our sun. When very large stars explode - or go supernova - they may leave behind a fairly massive remnant that can then collapse in on itself. Eventually, it can collapse to the point of having no volume and infinite density - at which point it is a black hole.

The birth of the black hole in real time delivers a little-appreciated message about our galaxy and universe: It is always changing. Stars are born and die. Black holes are created, grow bigger and over time wither.

The time scale is usually way too great for people to observe, but the baby black hole is a reminder that even the cosmos is forever in flux.

"This is the first time we've been able to observe what certainly appears to be a black hole form and grow," said Daniel Patnaude, an astronomer at the Harvard-Smithsonian Center for Astrophysics.

"It makes sense for us to think of the universe as existing now as it always has and always will because that's what we experience," he said. "But the last 20 years of study have shown that, in fact, the universe changes every single day in significant ways, and this apparent black hole is a dramatic example of that."

The theory that black holes exist was first put forward by J. Robert Oppenheimer, based Albert Einstein's work on general relativity. That black holes dot the cosmos is now a well-accepted fact in astronomy and cosmology. Although they define darkness, black holes - or at least the disk surrounding the hole and pulling matter into it - can be quite bright. That process creates friction and light as huge masses of swirling matter are pulled down into what might be thought of as a kitchen drain.

The possible birth of a new black hole was announced by the implosion of supernova 1979C, detected by backyard astronomer and then-middle school teacher Gus Johnson from Swanton, Md., when he saw a star suddenly brightening. The presence of the supernova was reported and soon was followed by astronomers using new and more powerful X-ray telescopes. Supernova 1979C was only the third one in a galaxy beyond the Milky Way directly detected from the ground, and it has become one of the most important and studied.

Although the exploded star is a seemingly vast 50 million light-years away, that is considered to be close and in our neighborhood of the universe.

The most persuasive data that astronomers were seeing a black hole came from the orbiting Chandra telescope, which confirmed previous information from other American and European X-ray telescopes that the X-ray emission from the imploded star was surprisingly steady. Usually, the X-ray radiation coming off a supernova decreases relatively quickly, and the fact that it did not over the 12 years it was observed strongly suggested that a black hole had been formed.

Several kinds of black holes exist in the universe, including "supermassive" black holes that appear to be at the center of most or all galaxies - sending out enormous jets of very high-energy gamma rays that can be readily detected. Stellar black holes such as the one just found are less likely than the supermassives to send out the gamma ray bursts and have to be detected in a different way.

"This may be the first time that the common way of making a black hole has been observed," said co-author Abraham Loeb of the Harvard-Smithsonian Center. "Most black holes in the universe should form when the core of a star collapses and a gamma ray burst is not produced."

Patnaude said that although the amount of matter falling into the new black hole is now small, it will increase as the mass of the black hole increases. Nonetheless, it will take another million years to double in size.

Although the scientists spoke Monday in terms of the black hole being 30 years old, it took 50 million years for the evidence to arrive, so the birth actually occurred long ago. It's only now that we're learning about it.