Telescope spots supernova explosion as it unfolds.
When stars explode, they generally do it so quickly that astronomers only spy the remnants of the event. But in a rare stroke of luck, a satellite has caught the X-ray burst of a dying star as the event actually unfolded.
The finding, which appears in today's issue of Nature1, confirms a decades-old theory that suggests such X-ray signals would occur as a result of supernovae. It also suggests that future missions will see many more stars in the act of exploding.
A star lives its life in a balancing act: gravity crushes its gas, while the energy of nuclear fusion pushes it back outward. But when a star runs out of fuel, gravity wins, and the star suddenly and catastrophically collapses. In massive stars, the rebound from that rapid compression is a massive explosion — a supernova.
Caught in the act
There is no way to predict exactly where and when in the Universe a supernova will occur, says Alicia Soderberg, a postdoctoral researcher at Princeton University in New Jersey. "It only lasts a few minutes and it is difficult to catch that signal," she says. Before now, astronomers were only able to look at the afterglows of supernovae.
That is exactly what Soderberg herself was doing on 9 January 2008, when she spotted the explosion. She was using NASA's Swift gamma-ray burst satellite to observe the remnants of a supernova in a nearby galaxy, when a sudden X-ray burst flared up. The X-ray flash lasted just minutes, but right away, she knew what she was seeing.
"I immediately triggered observations at all the telescopes I could get my hands on," she recalls. Observatories around the world turned their eyes to the distant galaxy and observed the explosion as it faded. The result is perhaps the most complete record of a supernova to date.
“I definitely won the astronomical lottery. Alicia Soderberg , Princeton University”
The sighting provides new clues about how the star died, she says. It seems to have been behaving perfectly normally up until the instant of its death. "It was going strong until the last minute," Soderberg says.
In those final minutes, the star's inner core suddenly and violently fell in on itself. According to theory, the core rebounded outwards, colliding with the star's outer shell and creating the X-rays caught by the Swift satellite.
The sighting confirms the theory that supernovae are accompanied by X-ray bursts, says Roger Chevalier, an astronomer at the University of Virginia in Charlottesville. "The amount of energy [the astronomers] see fits quite well with the model," he says.
Chevalier says that the team was lucky to catch the supernova in the act, and Soderberg agrees: "I definitely won the astronomical lottery."
But future observers may not have to rely on luck to make similar finds, she says. A new generation of X-ray telescopes is now being planned, which can observe wide swathes of the sky. Now that the presence of an X-ray supernova signature has been confirmed, these instruments should be able to spot similar explosions with great regularity. "The whole field of supernovae is really going to change," Soderberg says.
[Author]Soderberg, A. M.[/Author] et al. [Journal Title]Nature[/Journal Title] [Volume]453,[/Volume] [Pages]469–474[/Pages] ([Year]2008[/Year]).