Astronomers discover superflare as powerful as 80bn megatonne bomb

18 Apr 2019

An artist’s impression of the superflare erupting from the L dwarf star. Image: University of Warwick/Mark Garlick

Astronomers only discovered a star after it erupted with a ‘superflare’ 160m times more powerful than the largest hydrogen bomb ever detonated.

The universe’s ability to shock you with size continues following the discovery of an ultracool L dwarf star located 250 light years away named ULAS J224940.13-011236.9. Equivalent in size to Jupiter – or just one-tenth that of our sun – it should have been too faint for astronomers to see, but then something extraordinary happened.

In a paper published to the Monthly Notices of the Royal Astronomical Society: Letters, researchers from the University of Warwick revealed that the tiny star emitted a ‘superflare’ of incredible magnitude. It was estimated to have been 10 times more powerful than the so-called Carrington flare in 1859, the most powerful solar event seen to date.

The superflare occurred on the night of 13 August 2017 and was spotted over the course of a survey lasting 146 days. When it was flaring, it shone like a lighthouse to the astronomers as it was 10,000 times brighter than normal. At this point, the superflare had emitted the equivalent of 80bn megatonnes of TNT, or the equivalent of 160m times the yield of the largest hydrogen bomb ever detonated.

Flares are thought to be driven by a sudden release of magnetic energy generated in the star’s interior. This causes charged particles to heat plasma on the stellar surface, releasing vast amounts of optical, UV and X-ray radiation.

L dwarf stars are right at the limit of what we would call a star, having just enough mass to lie in the transition region between stars and brown dwarfs. These L dwarfs are very cool compared to common stars – such as red dwarfs – and emit radiation mostly in infrared, which may affect their ability to support life.

Burst of life

However, lead author of the study, James Jackman, said such an event might drastically change things for nearby planets.

“To get chemical reactions going on any orbiting planets and to form amino acids that form the basis of life, you would need a certain level of UV radiation. These stars don’t normally have that because they emit mostly in the infrared. But if they produced a large flare such as this one, that might kickstart some reactions.”

Speaking of what this means for future discoveries, Jackman’s PhD supervisor Prof Peter Wheatley said: “It is amazing that such a puny star can produce such a powerful explosion.

“This discovery is going to force us to think again about how small stars can store energy in magnetic fields. We are now searching giant flares from other tiny stars and push the limits on our understanding of stellar activity.”

Colm Gorey was a senior journalist with Silicon Republic