Little Cold Dwarf Star Fires Off A Monstrous Super-eruption
Ultracool L class dwarf star J0331-27 gave us such an x-ray mega-eruption that it shocked everyone. No astronomer has ever expected that such a little cold star could do something like this.
Image by Gerd Altmann from Pixabay
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Is It Even A Star?
The Universe around us has a lot of cold dwarf stars. In fact, they are the most common star in the Milky Way. They are really cold for a star and often we even doubt whether they are stellar, substellar, or even planetary objects. But that doesn't mean that these dwarves cannot get angry. And when they get angry they can fire off a stellar eruption that can shock us.
And an ultracool dwarf star J0331-27 recently gave us such a show. This object is an L class star – a very rare and incredible monster. It is so small that its mass is roughly only eight percent of the mass of our Sun. And guess what, it is exactly this mass where will differentiate between the smallest stars and the largest brown dwarves – or substellar objects. So let's just say this is an ultracool dwarf.
Eruption To End All Eruptions
It was exactly this dwarf that fired off an eruption a few years ago that it completely shocked astronomers. It was an x-ray eruption about ten times stronger than anything we would expect from the Sun based on everything we know about it. And it left scientists speechless. So far we thought that such small and low-energetic objects aren't capable of something like this. But obviously, they are.
Beate Stelzer and her colleagues from the Institut für Astronomie und Astrophysik Tübingen in Germany and the Osservatorio Astronomico di Palermo in Italy discovered this shocking super-eruption in older data from the European x-ray observatory XMM-Newton that came from 2008. And it is not just about the unbelievable intensity of this super-eruption as similar events are usually accompanied by a number of smaller eruptions. But the thing is, the ultracool dwarf only had this one giant x-ray eruption. Nothing else.
As far as we know such eruptions happen when the magnetic field in the atmosphere of an object destabilizes and a large amount of energy is released. The problem with the ultracool dwarf J0331-27 is that we would expect the need for a much higher temperature to accumulate such a large amount of energy. And J0331-27 just doesn't have it. The surface temperature of the dwarf is about 2100 degrees Kelvin. This is about three times less than the temperature of the surface of the Sun.
The researchers think that J0331-27 probably hoarded up energy for a long time and then fired it off all at once in a single spectacular super-eruption. This means our knowledge about L class stars is obviously incomplete. This has even been the first-ever x-ray eruption we detected in L class objects. Nonetheless, we are still missing a detailed explanation of the mechanism behind the massive eruption of the very cold dwarf. Just another mystery in the Milky Way to solve
Sources:
- http://www.sci-news.com/astronomy/xmm-newton-x-ray-superflare-ultracool-dwarf-08159.html
- https://www.aanda.org/articles/aa/abs/2020/02/aa37163-19/aa37163-19.html
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