Supernova SN 1987A--a massive stellar blast that went off 167,000 light-years away--announced itself 10 years ago with a flash of incredibly bright light, but the display is continuing. Now astronomers may have spotted the first sign of a new phase: debris from the explosion colliding with slow-moving rings of gas half a light-year from the center of the explosion. Scientists predict the collision will not only provide a dazzling show of light, x-rays, and other radiation, but also will help them understand the original explosion and the processes that created the rings long before the blast.
Astronomers believe supernovas like SN 1987A occur when massive stars run out of fuel, collapse under their own weight, and then explode. When the light from this one--as bright as 100 million suns--reached Earth, scientists had their best chance to observe how stars die. Seven years later, follow-up investigations with the Hubble Space Telescope revealed a puzzling trio of rings around the exploded star, probably gases thrown off by the precursor star tens of thousands of years before the explosion. Astronomers have been looking forward to seeing the so-far-invisible supernova debris catch up with these rings and collide with them, because the collision should light up the debris, revealing its elemental composition, speed, and direction. "You can only see the debris by having it hit something," says Peter Garnavich of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "We're expecting it to get really spectacular."
Now the show may have begun, Garnavich and his colleagues Robert Kirshner and Peter Challis reported last week on the Internet. In images from the Hubble Space Telescope, the researchers noticed a region just inside the inner ring that had brightened significantly in the last year. The bright spot matches an odd signal found this spring in an ultraviolet part of the spectrum. Those measurements suggested that something just inside the ring--likely a blob of gases--was moving toward Earth at 250 kilometers per second, more than 10 times faster than the gases in the ring. Astronomers couldn't be sure if the fast-moving gases had anything to do with the debris, but now, says astronomer George Sonneborn of NASA Goddard Space Flight Center in Greenbelt, Maryland, the new images suggest "there is really something going on there."
This detection comes slightly ahead of schedule. Theoreticians had predicted that the main collision wouldn't happen until around 2007. Kirshner cautions that a more detailed ultraviolet spectrum--planned for later this month--is needed to confirm that the brightening is due to the debris, rather than an ill-placed star.