Reaching magnitude +3 and easily visible to the naked eye, supernova 1987A was the closest and brightest supernova explosion since Kepler’s Supernova in 1604. It made a sudden appearance 30 years ago on February 23, 1987 in the Large Magellanic Cloud, a satellite galaxy of the Milky Way located 160,000 light years away in the southern constellation, Dorado the Goldfish. This week we celebrate its 30th birthday. Well, really 168,030th, since it happened 168,000 years ago. More about that in a minute.
You and I blow out the candles on our birthday cake, but SN 1987A was the candle and literally blew itself out! A blue supergiant star some 20 times more massive than the sun, the star formerly known as Sanduleak-69202 ran out of nuclear fuel in its core. With nothing left to “burn” to create the heat and pressure needed to stave off the crunch of gravity, the star collapsed. Material crashing down on the core set off a massive shock wave that rebounded outward through the once great sun, ripping it to pieces. The blast caused the once obscure supergiant to shine with the light of 10 billion suns as a supernova — a final show of glory marking the end of the star’s life.
Of course all this happened 168,000 years ago — the distance to the supernova — but the news took that long to reach the Earth traveling at the speed of light. To the eye, a “new” star appeared in the Milky Way’s satellite, but through telescopes, astronomers watched the shockwave of ejected material and bright light with every large telescope they could get their hands on including the Hubble.
The Hubble Space Telescope has been on the front line of observations of SN 1987A since it began operation in 1990 and has examined supernova many times over the past 27 years. To celebrate its 30th anniversary and follow its evolution, Hubble took another image of the distant explosion in January.
Because of its early detection and relative proximity to Earth, SN 1987A has become the best studied supernova ever. We’ve watched it evolve from a stellar explosion into a supernova remnant in superb detail, using telescopes in space and on the ground.
A remnant is what remains after the cataclysm and consists of an expanding cloud of gas, dust at the site of the supernova and the effects of the shockwave on material near the former star. Sometimes the core, now super-compressed after the collapse, remains intact as either a fast-spinning, particle-and-energy spitting pulsar or a black hole.
Back in 1990, Hubble was the first to see the event in high resolution, revealing the main ring that blazes around the exploded star. It also discovered the two fainter outer rings, which extend like mirror images in a hourglass-shaped structure. Even today, the origin of these structures is not yet fully understood, but may have been formed long ago, when an erstwhile companion star whipped up material in the outer atmosphere of the supergiant and sent it reeling into space.
However, by observing the expanding remnant material over the years, Hubble helped to show that the material within this structure was ejected 20,000 years before the actual explosion took place. Astronomers expected the dying star to eject material in a spherical shape, but faster stellar winds likely caused the slower material to pile up into ring-like structures. The shock wave from the explosion slammed into the inner ring in 2001, heating the gas to high temperatures and generating not only visible light but also strong X-rays.
The little balls of light in the inner ring almost seem to flicker over time like candles on that birthday cake. Mysteries remain. No sign has been seen of either a pulsar or black hole at the site of the explosion. Perhaps the thick cloud of dust there hides them from view — for now.