Astronomers Discover Explosive Double White Dwarf System Near Earth

Scientists at the University of Warwick have watched a very rare binary white dwarf star system which is to detonate as a type 1a supernova. The star system, called WDJ181058.67+311940.94, is about 150 light years away from our planet and the most massive and dense double white dwarf system which has been witnessed near our own solar system. Although the actual explosion will occur roughly 23 billion years from the present, its final brightness visible from Earth will even exceed the Moon in the nighttime sky.

The newly discovered star system comprises two white dwarfs, the dense remains of stars that have burned out their fuel. The two white dwarfs lie just 1/60th of the Earth-Sun distance apart. Now orbiting each other every 14 hours, the pair is slowly spiraling inwards because of the emission of gravitational waves. In the next billions of years, the slow spiral will get faster and faster until eventually the two stars will crash together in a super-dramatic explosion.

Its resulting supernova will be a type 1a supernova, a special kind of explosion which is used by astronomers as a standard candle to gauge distances in the universe. Type 1a supernovae are supernovae that occur when a white dwarf accumulates material from a companion until it gets to a mass at which it will explode. Its discovery confirms an old conjecture that double white dwarfs are primary cause systems for this phenomenon.

The total mass of this particular pair is 1.56 solar masses. This is above the Chandrasekhar mass, the mathematical mass threshold above which a white dwarf can no longer resist being drawn inwards towards collapse by gravity. At such a high-mass type of system, this one will always end in supernova, bar nothing else occurring in the instance. What is so exceptional about this system is not only its high mass but also that it is extremely close to Earth. The fact that it was discovered within our own galactic community suggests that these systems may be more prevalent than realized.

At the time of the peak stellar death spiral, the system will experience a very rare and complex quadruple detonation. That is when while one star increases in mass and begins to blow up, the process will initiate subsequent blows on the second star sequentially. The impact will be an immense energy release—roughly a thousand trillion trillion times that of a nuclear bomb—and annihilating the system completely.

The blast will be eye-blinding. It will glow, estimates say, a full ten times brighter than the Moon and about 200,000 times brighter than Jupiter when it finally explodes supernova. Though close by cosmic standards, the blast is not considered to be any threat to our planet.

This discovery fills a gap in the chain of what is understood about type 1a supernovae, which are of primary importance in the measurement of cosmic distances and charting the universe's expansion. The discovery of such a system within our own galaxy provides astronomers with a valuable point of reference and opportunity to probe existing theories on the creation of these high-energy cosmic events.

The research was made possible with the aid of some of the globe's most advanced optical telescopes, and involved international collaboration. Their findings are in Nature Astronomy, and the observation is the first-ever confirmed local binary white dwarf system on a collision course for this type of explosion.

The continuous survey by the team is meant to uncover more such systems to understand supernova mechanisms better. The discovery of the system close to Earth suggests that there may be more hidden systems in the galaxy, which means an over-anticipated rate of type 1a supernova progenitors.

Discovery of the binary white dwarf system WDJ181058.67+311940.94 is a landmark in stellar astronomy. Since it is the largest and most compact double white dwarf pair ever discovered so close to home, it confirms theories long held about the creation of type 1a supernovae and further research into stellar evolution. Even though the actual explosion will not occur another 23 billion years, its expected brightness and the fact that it offers scientists opportunities make it a top choice for future study. The find also illustrates the power of current astrophysical surveys and the potential for even more revolutionary discoveries in our own galaxy.

Source/Credits:
University of Warwick | Nature Astronomy | Image Credit: University of Warwick/Mark Garlick | Animation Credit: Dr. Ruediger Pakmor, Max Planck Institute for Astrophysics