BBC News | SCI/TECH | Stellar shockwave begins to glow

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BBC News Online: Sci/Tech

Friday, 18 February, 2000, 12:59 GMT

Stellar shockwave begins to glow

The stellar shockwave reaches the celestial ring

By BBC News Online science editor Dr David Whitehouse

The newly-refurbished Hubble Space Telescope (HST) is giving astronomers a view of a drama unfolding in an outrigger galaxy to ours.

In the Large Magellanic Cloud, a small companion galaxy to ours some 169,000 light-years away, astronomers are seeing the collision of fast-moving debris from an immense stellar explosion that occurred in February 1987. The gas ring that surrounds the site of the explosion is clearly visible.

The collision is causing the gases in the ring of ejected debris to glow as they are heated to millions of degrees and compressed by the sledgehammer blow of a 60-million-kilometre-per-hour (40-million-mph) blast wave.

In new pictures taken on 2 February, Hubble's sharp view has revealed four bright new knots of heated gas at places that had been fading slowly for a decade.

Unparalleled view

Two years ago, Hubble saw a single knot shine as it was first struck by the shockwave. "That was the opening jab. Now the dancing around is over and the slugfest will begin," says Robert Kirshner, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. The supernova seen from a distance...

"The real fireworks show is finally starting, and over the next 10 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, as well as radio and X-ray observations of the expanding supernova shockwave all led astronomers to anticipate that this 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 absorbed the full force of the crash.

Intense burst

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." ...and from close-up

Astronomers believe that the ring surrounding the site of the supernova explosion 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, but the ring has been slowly fading ever since then as the gas cooled.

The initial supernova flash only lit up a small part of the gas. 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 said. "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."

Related to this story:
Hubble looks through the keyhole (04 Feb 00 | Sci/Tech)
Hubble repair successful (14 Jan 00 | Sci/Tech)
Giant telescope's close-up on quasars (20 Jan 00 | Sci/Tech)

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