This week, astronomers have solved one supernova mystery and predicted a new one — to be solved in 2037.
Solving a 900-year-old Supernova Mystery
Almost a millenium ago, in 1181 AD, Chinese astronomers noted a "guest star" that appeared as bright as Saturn in their skies. This guest marked a supernova that gradually dimmed over the next six months before disappearing from naked-eye view. But even though they recorded an approximate location on the sky, no modern astronomer has been able to identify the supernova source.
Now, Albert Zijlstra (University of Manchester, UK) and colleagues announce the detection of the gaseous remnants of a supernova, a giant bubble expanding at about 1,100 km/s (2.5 million mph). Dana Patchick, part of the Deep-Sky Hunters amateur astronomer group, found the nebula in Wide-field Infared Survey Explorer (WISE) images.
Based on the current rate of expansion, the team estimates the gases originated in a supernova explosion some 1,000 years ago, at a point near the recorded location of the ancient guest star.
The supernova was likely the merger of two white dwarfs in a type of explosion astronomers classify as Type Iax, a rare beast that makes up only 10% of the supernova menagerie. The merger left behind an extreme stellar remnant that the researchers have dubbed "Parker's Star."
Ten billion years ago, a star exploded. Its photons journeyed through the universe, passing through a massive galaxy cluster some 6 billion years later. The gravity of those galaxies and their attendant retinues of hot gas acted like a cosmic lens, bending and magnifying the supernova's light, distorting it until it became multiple images.
Those images appeared in a Hubble Space Telescope photo in 2016 before fading away. By 2019, there was no visible remnant of the supernova, dubbed Requiem.
But we'll see Requiem again. By the way the cluster has bent the background light, astronomers predict that some photons took a fourth, longer path, and they'll take another 16 years to arrive. In 2037, astronomers will see if they're right.
Gravitationally lensed supernovae have been observed before (Supernova Refsdal and iPTF16geu are two notable examples), but the more of them the better. Because their light takes multiple paths to Earth, they are powerful probes of cosmology, giving astronomers an independent measure of the much-debated current expansion rate of the universe.