Tiny, cool star fires off enormous X-ray superflare
Astronomers have spotted a tiny, cool star putting on a stellar light show that would shame our Sun. This X-ray “superflare” was 10 times more powerful than anything the Sun can produce, and is completely unexpected for a star this small.
Known as J0331-27, the star belongs to a rare class called an L dwarf. With barely eight percent of the mass of the Sun, the object only barely scrapes over the line to even qualify as a star. As such, these stars weren’t thought to be particularly energetic.
But J0331-27 bucked expectations, unleashing a powerful X-ray flare that even a star 10 times bigger would be proud of. The flare was recently spotted in archival data dating back to July 5, 2008, recorded by the XMM-Newton X-ray observatory.
These flares are produced when a star’s atmospheric magnetic field becomes unstable and releases huge amounts of energy to space. The problem is, the build-up of energy was thought to require temperatures much higher than these cool stars are capable of.
“This is the most interesting scientific part of the discovery, because we did not expect L-dwarf stars to store enough energy in their magnetic fields to give rise to such outbursts,” says Beate Stelzer, a researcher on the study.
Weirder still, this was the only flare detected coming from J0331-27 during the 40 days of observations. The team found that odd – normally, if a star is going to throw a huge flare like that, it would be accompanied by smaller flares too.
“The data seem to imply that it takes an L dwarf longer to build up the energy, and then there is one sudden big release,” says Stelzer.
The study is the latest to call into question what we thought we knew about L dwarf stars. These cool little objects have already been seen to fire off superflares in visible light, but this is the first detected eruption at X-ray wavelengths, the team says.
The research was published in the journal Astronomy & Astrophysics.