In this picture, we capture the binary in the moment where the first white dwarf has just exploded, hurtling material towards its nearby companion which is on the cusp of explosion too. This event will occur in about 23 billion years, yet in only 4 seconds do both stars explode. (Credit: University of Warwick/Mark Garlick)
In a nutshell
- A ticking cosmic time bomb lies just 160 light-years from Earth: Astronomers have discovered a rare double white dwarf system, WDJ181058.67+311940.94, whose combined mass exceeds the Chandrasekhar limit, making it the first known nearby pair of dead stars destined to explode in a Type Ia supernova.
- This future explosion offers crucial insight into the universe’s expansion: Type Ia supernovae are vital tools for measuring cosmic distances. Finding a local system set to produce one helps scientists better understand how these standard candles form.
- We’re seeing theory meet reality, for the first time this close to home. While astronomers have long predicted that massive double white dwarfs should trigger these explosions, this discovery provides rare observational evidence that such systems not only exist but can eventually self-destruct in spectacular fashion.
WARWICK, England — Just 160 light years from Earth, two dead stars are headed towards chaotic destruction. These white dwarfs, the collapsed remains of once-ordinary stars like our Sun, have grown so massive together that they could one day merge and explode. While the cosmic fireworks won’t happen for another 23 billion years, this rare find is helping scientists finally understand the mysterious origins of some of the universe’s most important explosions.
The newly discovered system is called WDJ181058.67+311940.94. This pair of burned-out stellar cores orbit each other every 14.24 hours and together weigh 1.555 times the mass of our Sun, exceeding what physicists call the Chandrasekhar limit of 1.4 solar masses. Above this critical threshold, white dwarf stars become unstable.
For decades, astronomers have theorized that double white dwarf systems should frequently trigger Type Ia supernovae, but solid evidence was lacking. These powerful explosions happen when a dead white dwarf gets too heavy and blows up. No one had found a super-Chandrasekhar mass white dwarf pair in our stellar backyard that would eventually explode until now. Research published in Nature Astronomy reveals this is possible.
Since Type Ia supernovae all reach roughly the same peak brightness, astronomers use them to gauge vast cosmic distances. These measurements were key to the 1998 discovery that our universe’s expansion is speeding up, work that won the 2011 Nobel Prize in Physics and introduced the concept of dark energy.
A research team from the University of Warwick studied this white dwarf pair using several telescopes, including the Very Large Telescope in Chile and the Hubble Space Telescope. Their analysis confirmed that both stars are white dwarfs with carbon-oxygen cores, weighing 0.834 and 0.721 solar masses, respectively.
Don’t worry about this cosmic explosion disrupting our neighborhood anytime soon. The scientists calculated that gravitational waves will slowly bring the stars closer until they merge in roughly 22.6 billion years, long after our Sun burns out and becomes a white dwarf itself.
How the Two Stars Will Destroy Each Other
Computer simulations showed both stars will be completely destroyed through a “double detonation” process. As the stars begin to merge, a helium explosion will trigger on the surface of the heavier white dwarf, sending shock waves into its core. This ignites a second explosion that destroys the primary star. The shock wave then sets off a similar chain reaction in its companion, leaving nothing but an expanding cloud of debris.
When it finally blows, the explosion will appear as a slightly dimmer-than-average Type Ia supernova, reaching a peak brightness about 200,000 times that of Jupiter as seen from Earth. The blast will release enormous energy with radioactive nickel powering its light.
Based on this discovery, scientists estimate that these kinds of massive white dwarf pairs form fairly often in our galaxy. But the supernovae they eventually cause are still much rarer than expected, meaning other types of stars must be responsible for most of the explosions we see.
Another interesting finding is that white dwarf pairs like this contribute about the same fraction of supernovae as another rare type of system involving white dwarfs and hot subdwarf stars. Together, these two channels account for roughly 3% of all Type Ia supernovae in our galaxy.
More surveys to find additional systems like this one will be crucial for better understanding how common such pairs are in our cosmic neighborhood. Future space-based gravitational wave detectors will also help spot more of these systems throughout the galaxy.
The discovery of the first massive double white dwarf so close to home has given astronomers real evidence for a theoretical scenario discussed for decades. The cosmic timer is running on this stellar bomb, even if the explosion won’t happen until long after our Sun and Earth are gone.
Paper Summary
Methodology
Astronomers first spotted WDJ181058.67+311940.94 during the DBL survey, which specifically searches for double-lined double white dwarfs. The team collected data using multiple telescopes, including the William Herschel Telescope, Isaac Newton Telescope, Nordic Optical Telescope, and the Very Large Telescope, along with ultraviolet spectroscopy from the Hubble Space Telescope. They measured radial velocities from the hydrogen alpha line to determine the orbital period and motion of both stars, then used atmospheric fitting techniques to determine the temperature, surface gravity, and masses of both white dwarfs. Computer simulations using the AREPO code modeled what will happen when the stars eventually merge.
Results
The analysis confirmed that WDJ181058.67+311940.94 consists of two carbon-oxygen white dwarfs with masses of 0.834 ± 0.039 and 0.721 ± 0.020 solar masses, totaling 1.555 ± 0.044 solar masses – well above the Chandrasekhar limit. The stars currently orbit each other every 14.24 hours at a distance of about 0.016 astronomical units and will merge in 22.6 ± 1.0 billion years due to gravitational wave radiation. Simulations predict both stars will be completely destroyed in a sequence of detonations, resulting in a Type Ia supernova with an explosion energy of 1.2 × 10^51 ergs. Based on this discovery and one other similar system, researchers estimate a birth rate of super-Chandrasekhar mass double white dwarfs in the Milky Way of at least 6.0 × 10^-4 per year and a Type Ia supernova rate from such systems of approximately 4.4 × 10^-5 per year.
Limitations
The main limitation is statistical uncertainty when extrapolating galaxy-wide rates from just two discovered systems. The calculation relies on a simplified model of the Milky Way’s structure and assumes these systems are evenly distributed throughout the galaxy. Additionally, the DBL survey that found this system is only about 20% complete to its magnitude limit, suggesting more such systems likely exist nearby but haven’t been identified. The computer simulations also couldn’t directly model the ignition of carbon detonations due to resolution limitations, requiring manual triggering of detonations at expected convergence points.
Discussion and Takeaways
This discovery helps reconcile the gap between theory and observation regarding Type Ia supernova progenitors. The finding suggests roughly 3% of Type Ia supernovae in our galaxy come from double white dwarf or white dwarf plus hot subdwarf systems, with other mechanisms likely accounting for the remainder. The discovery highlights the need for continued searches for massive double white dwarf binaries in our local neighborhood, with future space-based gravitational wave detectors playing a crucial role in finding more such systems throughout the galaxy. This study demonstrates how modern astronomical observations and computational models can work together to predict complex stellar evolution processes.
Funding and Disclosures
The research received support from multiple funding agencies, including the Science and Technology Facilities Council, The Royal Society, the European Research Council, the Netherlands Research Council, and the Natural Sciences and Engineering Research Council of Canada. The study utilized telescopes including the European Southern Observatory’s Very Large Telescope, the William Herschel Telescope, the Isaac Newton Telescope, the Nordic Optical Telescope, and the Hubble Space Telescope.
Publication Information
The study, “A super-Chandrasekhar mass type Ia supernova progenitor at 49 pc set to detonate in 23 Gyr,” was published in Nature Astronomy on April 4, 2025. James Munday from the University of Warwick led the research, with collaborators from multiple institutions including the Max-Planck-Institut für Astrophysik, Instituto de Astrofísica de Canarias, Universidad de La Laguna, Radboud University, KU Leuven, SRON Netherlands Institute for Space Research, University of Amsterdam, and Harvard & Smithsonian Center for Astrophysics.
“While the cosmic fireworks won’t happen for another 23 billion years…”
Cool! I can’t wait to see that!