A pair of stars doomed to explode as a supernova discovered just 150 light-years away

The Institute of Astrophysics of the Canary Islands (IAC) has discovered an "extremely" rare binary system composed of two high-mass white dwarfs that are so close to each other that they will collide and give rise to a supernova.

Due to its proximity to Earth, this stellar explosion will be seen up to ten times brighter than the Moon, according to a study published in the journal Nature Astronomy, as reported by the IAC this Friday in a note.

Type 1a supernovae are a class of cosmic explosion used as a standard brightness reference to measure the expansion of the Universe.

They occur, adds the research center, when a white dwarf exceeds the Chandrasekhar limit —the maximum it can withstand without collapsing under its own gravity—, triggering a gigantic nuclear explosion equivalent to more than a quadrillion nuclear bombs.

It has been predicted for many years that the fusion of two white dwarfs, whose total mass exceeds this stability limit, could be the origin of most type 1a supernovae, but this is the first time that astronomers have found a system that will clearly end as a type 1a supernova.

"We have found many binary systems composed of two white dwarfs," says David Jones, researcher at the IAC and co-author of the study, "but no other that we know for sure is going to explode as a type 1a supernova."

"Not only are they very massive, with a total mass of more than 1.5 times the mass of the Sun," says James Munday, a doctoral student at the University of Warwick and first author of the article, "but they also have a very compact orbit, orbiting each other in just 14 hours, which means they will collide within 23,000 million 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 has been able to decipher the precise details of how it will end.

The orbit will slowly shrink due to the emission of gravitational waves until they complete an orbit in just 40 seconds, when the more massive white dwarf will begin to tear matter from its companion.

The accumulation of mass will cause a detonation on its surface causing another even larger explosion in its core. That eruption will launch matter in all directions at high speed, colliding with the companion and causing a repetition of the process for a third and fourth explosion, which will completely destroy the system.

"Although it is very close to our solar system, only 150 light years away, it does not represent any danger to Earth, but its brightness will be so intense that it can be seen with the naked eye during the day," the IAC concluded.