WASHINGTON (Reuters) - Excited astronomers said on Wednesday they had for the first time caught a supernova on camera just as it was exploding, and they may now learn how to spot others.

Light from supernovas in the NGC 2770 galaxy as imaged by the Gemini Multi-Object Spectrograph at Gemini North on Mauna Kea in Hawaii is seen in a handout image. REUTERS/Gemini Observatory/Handout

By luck, they spotted a burst of X-rays while looking at another part of a distant galaxy, and managed to turn a variety of telescopes in the right direction just in time.

“For years, we have dreamed of seeing a star just as it was exploding,” said Alicia Soderberg of Princeton University in New Jersey, who led the international team of astronomers.

“We were in the right place, at the right time, with the right telescope, on January 9th and witnessed history,” she added in a statement.

A supernova is a dying star, but one much bigger than Earth’s sun. It first explodes outwards, then shrinks into itself to form an extremely dense, cold ball. Sometimes a neutron star results and sometimes a black hole.

Soderberg’s team looked across space and time to witness the death throes of supernova 2008D, found in one arm of the galaxy NGC 2770, 88 million light-years from Earth.

In real time, they are seeing events that occurred 88 million years ago -- but in Earth time they are just occurring and the astronomers can watch the supernova as if it really were exploding just now.

“Using the most powerful radio, optical and X-ray telescopes on the ground and in space we were able to observe the evolution of the explosion right from the start,” said Edo Berger, who like Soderberg is a Carnegie-Princeton fellow.

“This eventually confirmed that the big X-ray blast marked the birth of a supernova.”

Soderberg and her colleagues were taking a scheduled look at NGC 2770 using the X-ray telescope on NASA’s Swift satellite. During that observation, a bright burst of X-rays came from one of the galaxy’s spiral arms, they report in this week’s issue of the journal Nature.

RUSH TO SEE

The 38-member international scientific team rushed to have a look with both orbiting and ground-based telescopes including the Chandra X-ray Observatory, Hubble Space Telescope, Keck I telescope in Hawaii, Palomar Observatory in California and National Science Foundation’s Very Large Array and Very Long Baseline Array radio telescopes.

They hope to gather information that will help astronomers spot other supernovas more quickly.

“Astronomical instruments planned for the future should then allow us to finally unravel the mystery of how these explosions occur,” Soderberg said.

Supernovas are usually spotted visually days to weeks after the first catastrophic explosion when a star flares up and then fades.

But the first burst creates a blast of particles known as neutrinos and a shock wave of kinetic energy that superheats the gas in the outer layers of the star. They in turn send out X-rays that can be the first clue of the fireball to come.

“This observation is by far the best example of what happens when a star dies and a neutron star is born,” said Kim Page of the University of Leicester in Britain, who led the X-ray analysis.

Last week astronomers said they saw the X-ray afterglow of a supernova in Earth’s own Milky Way galaxy that would have exploded 140 years ago, Earth-time.