Astronomers from the Max Planck Institute have identified the remnants of an enormous supernova just under 4,000 light-years from Earth. In apparent size, this expanding cloud of gas and dust spans nearly 100 times the diameter of the full Moon.
Supernovae mark the dramatic end of stars, triggered by two primary mechanisms. The first is a thermonuclear explosion in a white dwarf that accretes material from a companion star in a binary system. The second involves the core collapse of a massive star.
In both cases, the outcome is a cataclysmic explosion that ejects the star's outer layers as an expanding shell, temporarily outshining an entire galaxy. These events are crucial for cosmic evolution, forging the heaviest elements that enrich the universe.
Led by Werner Becker of Germany's Max Planck Institute for Extraterrestrial Physics, the team has uncovered the Hoinga supernova remnant—the largest known to date, named after a medieval village.
"In terms of apparent size, picture an expanding cloud of dust and gas roughly 90 times larger than the full Moon," Becker explains.
Hoinga evaded detection until now because it emits primarily in X-rays, visible only to advanced telescopes like eROSITA. Launched in 2019 aboard the Russian-German SRG satellite, eROSITA is 25 times more sensitive than its predecessor, ROSAT.
"We anticipated new supernova remnants soon, but finding one this quickly is a thrilling surprise," notes Natasha Hurley-Walker from Australia's International Centre for Radio Astronomy Research.
Radio observations date Hoinga to 21,000–150,000 years old, located 1,470–3,915 light-years away.
Its position high above the galactic plane—away from typical stellar nurseries—adds to the intrigue. Archival data from arXiv confirms faint traces in 30-year-old ROSAT images.
"Supernova remnants aren't usually sought at high galactic latitudes, so many more may lurk undetected," Becker observes.
