Astronomers have spotted a titanic flare on a young star 685 light years away, a huge explosion 10,000 times more powerful than the largest solar flare ever recorded from the Sun. Such outbursts may play a role in the formation and evolution of exoplanets, but the jury is still out on whether the effects are generally positive or negative.
The M-type star in question is known as NGTS J121939.5-355557, and it is only about 2 million years old. It was found by University of Warwick doctoral student James Jackman using the Next-Generation Transit Survey telescope array in Chile.
“This is normally a star that shows little activity and stays a constant brightness,” he said. “Then, on this one particular night, we saw it suddenly grow seven times brighter than normal for a few hours, which is pretty extreme. And then after that it goes back to normal.
“We see these types of flares on the Sun, but nowhere near as big as this. On our Sun, you can do incredibly detailed studies on this kind of activity. It’s difficult to extend that understanding to other stars because the data we need hasn’t been available until now.”
Stellar flares occur when a star’s magnetic field rearranges itself, releasing enormous amounts of energy and accelerating electrically charged particles that crash into the surface generating extreme temperatures, along with X-rays, gamma rays, optical and infrared light.
The magnetic fields on M-class stars are more powerful than those of the Sun but it’s estimated that flares like the one observed by Warwick only occur every three years to twice a decade.
“This is an incredibly young star, only about 2 million years old,” Warwick said. “You’d call it a baby, it’s going to live for ten of billions of years, so it’s in the first one percent of its lifetime.
“Even though it’s much cooler than our Sun by about 2,000 degrees it is roughly the same size, but pretty large for an M star. This is because it’s still being formed from gas in the disc and contracting and cooling until it reaches the main sequence, staying at a certain radius and luminosity for billions of years.”
X-rays from such powerful flares are thought to play a role in the formation of “chondrules,” or calcium-aluminium-rich grains in a star’s protoplanetary disc that eventually coalesce into asteroids and, eventually, planets. A major question is what impact such flares have on planet formation.
“A massive flare like this could be advantageous for planet formation, or it could be disruptive,” said Peter Wheatley, Jackman’s Ph.D. supervisor. “This particular star won’t have formed its planets yet, so this type of flare activity is something that astronomers will need to take into account when considering planet formation.
“There’s a discussion at the moment around whether flares are a good or bad thing for life on orbiting habitable planets, because they output a large amount of UV radiation, he added. “That could cause biological damage to surface organisms and damage their DNA. On the other hand, UV radiation is required for various chemical reactions to start life and that’s not typically provided in great enough quantity by these types of stars. These flares could potentially kickstart these reactions.”
The flare is discussed in a paper for the Monthly Notices of the Royal Astronomical Society.