how a flare with the power of a quarter of a trillion nukes could create life

An immensely powerful flare from a tiny red dwarf is helping us understand just how important these stars can be to giving life across the universe to chance to develop.

ULAS J224940.13−011236.9 is technically a star, although it doesn't burn much hotter than a typical flame and is roughly the size of Jupiter. Any lighter or cooler and it would be classified as a brown dwarf instead, which already makes it an interesting object to study if you're interested in learning how to better differentiate and classify the many spheres of rock, gas, and plasma floating around in space. But besides just being an edge case in astronomy, it's attracting a lot of attention by putting out a flare which momentarily turned it 10,000 times brighter, making it one of the biggest events ever recorded for a L dwarf star.

Just to give you some idea how much energy that required, imagine 250 billion typical nuclear warheads, making which would require us to mine virtually all of the 40 trillion tons of uranium estimated to exist on Earth and convert a great deal of it into plutonium, going off at the same instant. The most powerful earthquakes our planet could produce exert only a billionth of the intensity observed from the little star. And this should raise the obvious question of how exactly one of the smallest things we can still define as a star could even be capable of a blast that powerful. Surprisingly, its low mass is a key part of the answer.

Heavier stars like ours have clearly defined convection layers thanks to the effects of gravity on the broiling plasma in their innards. As the plasma is closer to the core, it becomes denser and its movement settles. Red dwarfs, however, convect throughout, some even to their very cores, building up immensely powerful magnetic fields that trap supercharged plasma in loops as it swirls, heating up and building more and more energy, like planet sized rubber bands on fire, stretched right up to their breaking point. Eventually, they snap, unleashing the built up tension in a single energetic event, bathing the star's inner solar system in a shower of lethal radiation and lighting up astronomers' screens.

A similar process involving dust from dead stars is thought to power FRBs, or fast radio bursts, most likely generated by magnetically supercharged neutron stars called magnetars. And while the radioactive tsunami it unleashes could pose a lot of trouble for any alien life that managed to evolve on nearby planets, as well as potential human explorers centuries from now, it could also play a role in creating new living things. Amino acids frequently carried by comets and asteroids to young planets, and other precursors to life abundant in protoplanetary disks, need a burst of energy to start combining into the sort of sustainable biological chemistry we'd call life. Without that burst, any primordial soup would bubble with nothing more than potential.

Potent UV flares could easily do the trick, so if even the smallest, coldest stars are capable of producing them, they may also be capable of helping alien microbes emerge and let evolution take it from there. This is a really big deal because red dwarves make up 7 out of 10 stars in the entire observable universe, and can live between 100 billion and 10 trillion years depending on their size. If we find complex or intelligent alien life, statistically speaking, it will be on a tidally locked world around a star not too dissimilar from ULAS J224940.13−011236.9 in behavior, temperature, and composition. So, while red dwarves may not be as exciting as massive and powerful supergiants that collapse into ravenous black holes, or even more exotic high mass and high density objects, they are some of the most important stars to study because they and their solar systems hold the most promise for life, exploration, and colonization.

See: Jackman J., et al. (2019) Detection of a giant white-light flare on an L2.5 dwarf with the Next Generation Transit Survey, Monthly Notices of the Royal Astronomical Society: Letters DOI: 10.1093/mnrasl/slz039