NASA's Hubble Space Telescope is giving astronomers a ringside seat to a never-before-seen violent celestial "main attraction" unfolding in a galaxy 169,000 light-years away. The knockout event is the collision of the fastest moving debris from an immense stellar explosion seen in February 1987 with the gas ring that circles that site.
This collision is beginning to cause the gases in the ring to glow as they are heated to millions of degrees and compressed by the sledgehammer blow of a 40 million mile-per-hour blast wave. In new pictures taken on February 2, Hubble's sharp view revealed four bright new knots of heated gas at places that had been fading slowly for a decade. Under an observing program called the Supernova Intensive Survey, a team of astronomers that has been monitoring supernova 1987A (SN1987A) with Hubble since it was launched in 1990.
One of the first clues to the celestial fireworks came in 1997 when Hubble saw a single knot in the ring shine like a bright diamond as it was first impacted by the shockwave. "That was the opening jab. Now the dancing around is over and the slugfest will begin," says Robert Kirshner of Harvard-Smithsonian Center for Astrophysics in Cambridge, MA.
"The real fireworks show is finally starting, and over the next ten years things will get spectacular. It helps that Hubble is giving us an unparalleled view," adds Peter Garnavich of the University of Notre Dame.
Previous Hubble spectroscopic observations, and radio and x-ray telescopic observations of the expanding supernova shockwave all led astronomers to anticipate that the titanic collision was only a matter of time. As far back as 1992, astronomers predicted that the ring would become ablaze with light as it absorbs the full force of the crash.
Upon seeing the new Hubble pictures, Kirshner remarked, "It's about time. We saw that first hotspot two years ago, but I was getting nervous that we might have been mistaken about its location. It's great to see the shockwave start to light up the ring."
SN1987A has long puzzled astronomers. They believe the ring is made up of old gas that was ejected by the star 20,000 years ago, long before it exploded. The ring's presence was given away when it was heated by the intense burst of light from the 1987 explosion. The ring has been slowly fading ever since then as the gas cools.
The initial supernova flash only lit up a small part of the gas that surrounds the supernova. Much of it is still invisible. But the light from the crash should illuminate this invisible matter for the first time, and help unravel the mystery of a pair of outer rings seen around the supernova as well.
"Now as the central ring begins to light up again, we can see how this old material is arranged around the star. We can map its distribution," Kirshner says. "This event gives us another chance to see the true structure of the gas around the supernova and to puzzle out how it got there."
Kirshner and his colleagues plan to use Hubble to do follow-up observations later this year to track the ongoing drama of one of the biggest celestial collisions ever witnessed by astronomers.