Shortly after, the shock wave pierces the star's surface, blasting it apart and strewing its luminous debris across light-years of space. (See related images of supernova remnants.)
"We caught the star while the supernova shock wave approached the surface of the star and then blew it apart," Schawinski said.
Peter Nugent is an astrophysicist at the Lawrence Berkeley National Laboratory in California who was not involved in the study.
Nugent called the latest breakout detection "incredibly exciting."
"You can literally see the shock coming through the undisturbed atmosphere of the red giant star and then the subsequent expansion of that star," Nugent said.
The discovery allows astronomers to analyze the properties of a dying star in the moments before it goes supernova, data that are almost impossible to measure, he added, "unless one went off in our own galaxy."
The red supergiant's shock breakout was discovered using a combination of ground and space telescopes.
The Supernova Legacy Survey in Hawaii first detected visible light from the distant supernova, called SNLS-04D2dc, several weeks after it had already exploded.
To look for the earlier shock breakout, the team combed through a backlog of data collected by the Galaxy Evolution Explorer (GALEX), a NASA space telescope that scans in ultraviolet wavelengths.
Their search revealed a bright ultraviolet burst in the precise location of the supernova about three weeks before the explosion.
The previous team to detect a shock breakout witnessed the death of a rare compact blue star while examining images from NASA's Swift X-Ray Telescope.
But that discovery was very serendipitous and unlikely to be repeated, said Brian Schmidt, an astrophysicist at Australian National University who was not involved in either study.
"They were a million-to-one lucky," Schmidt said.
By contrast, the detection of the red supergiant shock breakout relied on diligent detective work.
"They did this without being lucky but by being systematic and sifting through huge amounts of data," Schmidt said.
The technique used by Schawinski's team could be more easily repeated and used to discover similar breakouts.
SOURCES AND RELATED WEB SITES