New activity near Supernova 1987A.

Seven years ago this week, astronomers witnessed the birth of the first supernova visible to the naked eye in nearly 400 years. Supernova 1987A began fading from view in mid-1987 and has stayed dim ever since. But just in time to mark the seventh anniversary of this event, astronomers have found that a ring of gas surrounding the remains of this exploded star has brightened. E. Joseph Wampler of the European Southern Observatory in Garching, Germany, says the brightening may be a prelude to the fireworks expected some 4 years from now, when the densest part of the supernovas blast wave slams into the gas ring.

Wampler and Li-Fan Wang of the Beijing Astronomical Observatory viewed the ring in visible light last December using the New Technology Telescope in La Serena, Chile. Some parts of the ring were emitting more visible light than at any time during the past 2 years, they report in a Jan. 27 circular of the International Astronomical Union.

The ring predates the supernova. Fierce winds from the supernovas parent star provided the raw material for the gas ring and sculpted it. But the ring only became visible after radiation from the supernovas blast wave heated it. The recent brightening indicates that the outermost layers of the fireball have begun to catch up and collide with the ring. Ultraviolet light produced by the encounter would ionize gas in the ring and cause it to glow in visible light, Wampler says.

The brightening may herald a violent interaction between the ring and the interior of the supernovas fireball, which moves more slowly and has a higher density than the exterior portions. This encounter, which might begin in 1997, will illuminate the ring dramatically and eventually distort it. By observing such changes, researchers hope to learn more about the shape and velocity of the fireball.