1987

Supernova 1987A

If a star is massive enough—perhaps 8 to 10 times the Sun’s mass—stellar evolution models indicate that once it converts all of its hydrogen to helium it will eventually end its life in a gigantic explosion called a supernova. Astronomers believe that a supernova explosion goes off in the Milky Way galaxy about once every 50 years or so. Most are too distant to notice, or are obscured by dust in the galactic plane. Chinese astronomers recorded a number of “Guest Stars” over the centuries, including one in 185 and a “Daytime Star” supernova in 1054 that eventually formed the Crab Nebula. In 1572 Tycho Brahe obtained detailed observations of a supernova in the constellation Cassiopeia, and in 1606 Johannes Kepler wrote an entire book about a bright supernova in Ophiuchus that had occurred two years earlier. Kepler’s supernova of 1604 is still the most recent known stellar explosion in our galaxy.

Modern astronomers finally got the opportunity to study a supernova “up close” when the blue supergiant star Sanduleak −69° 202 suddenly exploded on February 23, 1987, becoming Supernova 1987A. The explosion actually occurred 168,000 years earlier in the Large Magellanic Cloud, one of the Milky Way’s dwarf satellite galaxies, but it took that long for the light to arrive at Earth. The star increased in brightness by a factor of about 4,000, becoming a naked-eye object to observers all over the world for more than six months before it faded.

Astronomers used Supernova 1987A as a grand cosmic experiment to understand stellar evolution and high-energy processes. Optical and infrared telescopes around the world, and ultraviolet, X-ray, optical, and infrared telescopes in space observed the event and its aftermath. Just three hours before the visible explosion, neutrinos were detected at multiple observatories, confirming the core-collapse model for supernova explosions. In the past few years astronomers have watched the shock waves from the main explosion crash into a shell of previously ejected gas from the dying progenitor star.

Some stars die spectacular, violent deaths. One wonders whether any planets and their inhabitants were also destroyed in these cataclysmic events, and when the next supernova might go off in our neck of the galaxy. We seem overdue.

Hubble Space Telescope photo of the bright speckled ring of light surrounding the remnants of Supernova 1987A (center). The ring is caused by powerful shock waves traveling outward from the exploding star. The two bright bluish stars in the foreground are unrelated to the supernova.