The heaviest stars are notably absent among observed supernovae. Common, hydrogen-rich, supernovae (Type II) appear to come from stars less massive than 20 times the mass of the sun. It has been suggested that perhaps heavier stars collapse directly into black holes without any kind of supernova explosion.

In the latest issue of Nature Astronomy Joe Anderson and co-authors describe a possible exception. Anderson works at the European Southern Observatory in Chile and has studied the supernova SN 2015bs, which seems to originate from a star that is up to 25 times more massive than our sun. They found this supernova by searching in unusually faint metal-poor galaxies.

Supernova SN 2015bs is 390 million light years away in the constellation Aquarius. It belongs to the most common kind of supernova, but contains less heavy elements such as iron, silicon, and oxygen. Jesper Sollerman, professor at the Oskar Klein Centre at Stockholm University, co-author of the article says: "The discovery of this supernova is the fruit of a fairly systematic investigation of stellar explosions in the faintest galaxies - a different approach than the strategy that has been utilized the last 20 years."

Previously it was routine to search the largest galaxies because this is where it is easiest to find supernovae. The results of those searches give a biased selection of what kind of explosions one can find.

The supernova group in Stockholm has been working on these questions for several years, says Jesper Sollerman. Type II supernovae in the most metal-poor galaxies were studied in 2016 by post-doc Francesco Taddia. Soon, Emir Karamehmetoglu defends his Licentiate thesis on supernovae from the more massive stars.

Future systematic surveys of smaller galaxies will be facilitated by our new camera at Palomar in California, concludes Sollerman. There will be more of these types of discoveries.