BEIJING, July 19 (Xinhua) -- A scientist from the U.S. National Aeronautics and Space Administration (NASA) said here on Wednesday that tremendous progress has been made in understanding the most powerful explosions in universe, the gamma-ray burst.

Delivering a speech at the 36th Committee on Space Research Scientific Assembly, Neil Gehrels, from NASA said gamma-ray bursts are among the most fascinating occurrences in the cosmos.

"They are thought to be the birth cries of black holes throughout the universe," Gehrels said.

NASA launched a satellite, Swift, in November 2004, carrying an international multi-wavelength observatory designed to determine the origins of the gamma-ray bursts and use them to probe the early universe, he said.

During its two-year mission, Swift is expected to observe more than 200 gamma-ray bursts.

Three instruments of Swift work together to observe gamma-ray bursts and afterglows in the gamma ray, X-ray, ultraviolet, and optical wavebands.

He said the satellite would determine the origin of gamma-ray bursts, classify gamma-ray bursts and search for new types, determine how the blast waves evolved and interacted with the surroundings, use gamma-ray bursts to study the early universe.

"A huge step forward has been made in our understanding of the mysterious short gamma-ray bursts," Gehrels said.

He said two types of gamma-ray bursts had been identified: the long bursts lasting for tens or hundreds of seconds, and shorter ones lasting a few milliseconds to a second. They had different origins.

There was sufficient research evidence to show that long bursts were the death throes of massive stars in distant, young, and vigorously forming galaxies, while the origin of the short gamma-ray bursts had been shrouded in mystery until now.

In December 2005, the first study that accurately pinpointed a short gamma-ray burst to an old galaxy, implying that a population of old neutron stars were the sources of these explosion, was released.

The advent of NASA's Swift satellite and the rapid follow-up by the ground-based telescopes would help to localize the short gamma-ray bursts. Enditem