NASA's Hubble Space Telescope has provided a dramatic new look at the remnants of one of the most spectacular and unexpected astronomical events of this century, the great supernova of 1987.
Observations made with the European Space Agency's Faint Object Camera, on August 23-24 have provided, with unprecedented sharpness and clarity down to 0.1 arcsecond, an intriguing view of the supernova and its surrounding shell of stellar material. The image, taken in visible light, reveals the details of the circumstellar shell, whose characteristics had been previously suggested by ground based observations and data from the International Ultraviolet Explorer satellite.
This new image will provide important insights into the evolution of massive stars and their catastrophic deaths as supernova explosions.
The visible light image clearly shows an elliptical, luminescent ring of gas about 1.3 light-years across surrounding the still glowing center of the 1987 explosion. The ring is a relic of the hydrogen-rich stellar envelope that was ejected, in the form of a gentle "stellar wind" by the progenitor, which was a red supergiant star that existed an estimated 10,000 years before the explosion took place.
This diffuse gas was subsequently swept and compressed into a narrow, high-density shell by a high-speed stellar wind ejected from the star when it evolved back to a blue supergiant stage. The image suggests that the star was more efficient at compressing gas along an equatorial plane, to create a ring-like structure. Because the ring is inclined along the line-of-sight it has an elliptical appearance.
In the first few hours following the supernova blast the ring was fully ionized and heated by a flood of ultraviolet radiation. Three and a half years later the ring still glows at a temperature of more than 20,000 degrees Kelvin.
The slowly expanding ring is destined to be a relatively short-lived structure. It will be overtaken by the swiftly moving (1/10 speed of light) ejecta from the supernova in a few more years. This collision will heat the ring such that it will brightly glow in X-ray and ultraviolet light. Within a few decades the ring will be completely engulfed by supernova debris which will be visible for centuries as a bright supernova remnant.