A study published today in Nature Astronomy, in which a researcher from the IAC has participated, outlines the discovery of an extremely rare type of binary system composed of two high mass white dwarfs.  The two stars are so close together that they will eventually collide resulting in a supernova explosion which, due to its proximity to the Earth, will appear ten times brighter than the Moon.

Type 1a supernovae are a class of cosmic explosion often used as "standard candles" to measure the expansion of the Universe.  They occur when a white dwarf exceeds the Chandrasekhar mass - the limit above which it cannot withstand its own gravity - leading to collapse and an explosion equivalent to more than a thousand trillion trillion nuclear bombs.  Many years ago, it was predicted that the merger of two white dwarfs, the total mass of which exceeds this limit for stability, could be the pathway by which a majority of type 1a supernovae form, but this is the first time that astronomers have discovered a system that will definitively lead to a supernova explosion.  "We've found lots of double white dwarf binaries" says David Jones, researcher at the IAC and coauthor of the article, "but no others that we are so certain will explode as a type 1a supernova".

"It's not just that they are both very massive, with a total mass of more than 1.5 times the mass of the Sun" says James Munday, PhD student at the University of Warwick and lead author of the study, "but also that they are very close together, orbiting around one another in only 14 hours.  Together this means that the two stars will collide within the next 23 billion years."

Using data from the Nordic Optical Telescope and William Herschel Telescope, both located at the Roque de Los Muchachos Observatory (Garafía, La Palma), the team was able to understand the precise details of how the two stars will reach their demise.  Initially, their separation will shrink slowly due to the emission of gravitational waves until the orbital period reaches only 40 seconds, at this point the more massive of the pair will begin to strip material from its companion.  The accumulation of mass will lead to a nuclear detonation on its surface which will in turn cause another even larger explosion in the star's core.  This eruption will launch matter in all direction at great speed, when this material hits the companion it will cause the whole process to repeat, leading to the third and fourth explosion, ending the complete destruction of the system.

Even though the explosion will be very close to our own Solar System - only 150 light years away - it won't present any great risk to life on Earth, but it will be so bright as to be seen by the naked eye even during the hours of daylight.

Article: James Munday, et al. "A super-Chandrasekhar mass type Ia supernova progenitor at 49 pc set to detonate in 23 Gyr". Nature Astronomy, 2025. DOI: 10.1038/s41550-025-02528-4

Contact at the IAC:
David Jones, david.jones [at] iac.es (david[dot]jones[at]iac[dot]es)