Scientists are on the verge of looking into the heart of darkness. Astronomers are closing in on proof that a supermassive black hole is the source of mysterious radio waves at the center of our galaxy, the Milky Way.

Using a worldwide array of radio telescopes to obtain the most detailed look yet at the center of the Milky Way galaxy, astronomers said that they had narrowed the size of a mysterious fountain of energy there to less than half that of the earth's orbit about the sun.

The result strengthens the case that the energy is generated by a massive black hole gobbling stars and gas, they said. And it leaves astronomers on the verge of seeing the black hole itself as a small dark shadow ringed with light, in the blaze of radiation that marks the galaxy's center.

Black holes are objects whose gravitational pull is so strong that nothing, not even light, can escape. Supermassive black holes contain the mass of millions, if not billions, of suns.

Astronomers have long suspected that supermassive black holes sit at the heart of most galaxies and may be closely related to galaxy growth. But concrete proof of the existence of these black holes has remained elusive.

This is less than half the size previously estimated, indicating that astronomers are close to defining the crucial outer boundary of one of the most elusive phenomena in cosmology -- one that has mystified scientists for decades.

"We're getting tantalizingly close to being able to see an unmistakable signature that would provide the first concrete proof of a supermassive black hole at a galaxy's center," Shen Zhi-Qiang of the Shanghai Astronomical Observatory, one of the leaders of an international team of radio astronomers, said in a news release. Their report appears today in the English journal Nature.

The white circle is where scientists believed to be a supermassive black hole.

Fred Lo, director of the National Radio Astronomy Observatory in Charlottesville, Va., said that achieving the extra resolution could take several years and would probably require new radio telescopes. "We're not there yet, but in time no question, we will get there." He added that seeing the shadow, would be "proof of the pudding" that Einstein was right and that black holes exist.

Further refinements and new instruments may allow astronomers to eventually capture an image of a distinctive shadow around the black hole.

The shadow is caused by radiation from sources that cross the so-called event horizon, the point of no return surrounding a black hole.

"That would really put the nail in the coffin," Lo said.

(Xinhua News Agency November 4, 2005)