• Astronomers discovered an extremely rare, high mass, compact binary star system only 150 light years away. These two stars are on a collision course to explode as a type 1a supernova, appearing 10 times brighter than the Moon in the night sky.

• A light-year is the distance light travels in a year, 9.5 trillion km.

• Type 1a supernovae are a special class of cosmic explosion, famously used as ‘standard candles’ to measure distances between Earth and their host galaxies. 

• They occur when a white dwarf (the dense remnant core of a star) accumulates too much mass, is unable to withstand its own gravity, and explodes.

What is white dwarf?

A white dwarf is the stellar core left behind after a dying star has exhausted its nuclear fuel and expelled its outer layers to form a planetary nebula. Stars with up to eight times the mass of our Sun appear destined to end up this way. The ultimate fate of a star depends on its initial mass. There are several possible ways in which certain stars might eventually become white dwarfs. The vast majority of white dwarfs are formed after a dying star has shed its outer layers to form a planetary nebula, leaving behind an approximately Earth-sized inner core that is the white dwarf. 

When will it explode?

• It has long been theoretically predicted that two orbiting white dwarfs are the cause of most type 1a supernova explosions. When in a close orbit, the heavier white dwarf of the pair gradually accumulates material from its partner, which leads to that star (or both stars) exploding.

• The explosion is not due for another 23 billion years, however, and despite being so close to our solar system, this supernova will not endanger our planet, the researchers said.

• This discovery, published in Nature Astronomy, has not only found such a system for the first time, but has found a compact white dwarf pair right on our doorstep in the Milky Way.

• Right now, the white dwarfs are leisurely spiralling around each other in an orbit taking longer than 14 hours. Over billions of years, gravitational wave radiation will cause the two stars to inspiral until, at the precipice of the supernova event, they will be moving so fast that they complete an orbit in a mere 30-40 seconds.

• For the supernova event, mass will transfer from one dwarf to the other, resulting in a rare and complex supernova explosion through a quadruple detonation. 

• The surface of the mass-gaining dwarf detonates where it is accumulating material first, causing its core to explode second. This ejects material in all directions, colliding with the other white dwarf, causing the process to repeat for a third and fourth detonation.

• Billions of years into the future, this supernova will appear as a very intense point of light in the night sky. It will make some of the brightest objects look faint in comparison, appearing up to ten-times brighter than the Moon and 200,000 times brighter than Jupiter.

(The author is a trainer for Civil Services aspirants.)