About 170,000 years ago, a star exploded in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. When light and neutrinos from this explosion reached the Earth in 1987, SN1987A became the brightest supernova seen since 1604 â and the best studied ever.
Eleven years later, a second light show is beginning. The blast wave from the original explosion has finally reached a dense and mysterious ring of gas surrounding the star. Its first contact can be seen in these Hubble Telescope images, which show a small patch of the ring suddenly brightening.
What produced this ring? It may have been thrown off by a merger between the main star and a binary companion, some 20,000 years before the explosion.
That idea is appealing because it could also explain why the progenitor star was a blue supergiant, instead of the red supergiant that usually precedes this type of supernova. But the ring could instead be the waist of a more extended shell of gas, emitted as a dense stellar wind in a passing stage of the precursor star's evolution.
Within a year or two we may know better. As the shockwave passes through at 18,000 km sâ1, it will heat the gas. The ring will then shine brightly, allowing highly detailed spectroscopy and imaging, and illuminating gas elsewhere in the system.
It is a familiar story â often, the best way to learn about an object is to watch what happens when something hits it.
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Battersby, S. Supernova 1987A Shockwave hits the ring. Nature 391, 741 (1998). https://doi.org/10.1038/35742
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DOI: https://doi.org/10.1038/35742
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