The protracted explosion of a star ended up lasting more than three years — ten times the typical lifetime of a supernova blast.
Most stars that become supernovae explode in a single burst that trails off over about 100 days. But in 2017, astronomers announced the discovery of a rare supernova known as iPTF14hls, which continued to shine after more than 600 days, despite its otherwise conventional appearance. Astronomers think it erupted once before, in 1954.
Using a total of seven ground- and space-based telescopes, including the Hubble Space Telescope, Jesper Sollerman at Stockholm University and his colleagues found that the exploding star’s light eventually faded after more than 1,000 days. The light trailed off steeply — a puzzling feature not predicted by most explanations of the supernova’s strange behaviour.
The light contained the signature of sulfur, which was probably produced deep in the supernova’s core. The researchers say that the presence of this element may help them to rule out some potential explanations. A series of blasts in the star’s outer layer, for example, might account for the light pattern, but would probably not produce sulfur.