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Do brown dwarfs have spots and faculae similar to other heavier stars?


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So far, opinion is divided, as evidence has not been found to prove either way. Back in 2015, a study published in Nature, and linked via the Verge, here suggested that no, brown dwarfs do not exhibit star-like behaviours, but are in fact much closer to planets (due to them being below critical mass for hydrogen fusion in their cores)

All planets that have magnetic fields within our Solar System have aurorae, so Hallinan and other researchers believed that if brown dwarfs were more like planets, they too would exhibit aurorae.

...each time LSRJ 1835+3259 rotated — every 2.84 hours — it pulsed a radio emission and an aurora appeared at a location on the brown dwarf's surface.

..."In the case of the brown dwarf, the aurora is so much more powerful than anything we've seen in our Solar System," says Hallinan. "Jupiter's aurorae are 1,000 times more powerful than the Earth's aurorae. Well this brown dwarf has aurorae that are at least 10,000 times more powerful than Jupiter's aurora." The aurorae's colors are also a bit more diverse, emitting red along with blue and green.

...it strengthens the argument that brown dwarfs are more closely related to planets, kind of like "beefed-up Jupiters." "Typically, people tend to think of these things as failed stars," says Nichols. "My preferred explanation is they’re more like very successful planets, and this study demonstrates more planet behavior than stellar behavior."

However this 2017 article in the Astrophysical Journal which looked at the same data from LSRJ1835+3259 suggests otherwise, identifying the magentic data not as aurorae, but as effects more like that of our own sun. A nice summary of the article on Howstuffworks.com:

As the object rotated, a powerful magnetic region came into view, more powerful than the magnetic fields associated with sunspots that we observe on the sun. Sunspots are magnetically active regions that can trigger coronal mass ejections, solar flares and produce powerful streams of solar wind — all of which can generate powerful geomagnetic storms on Earth.

In an interview with New Scientist, the researchers point out that LSR J1835+3259 is very young (approximately 20 million years old) and the powerful magnetic field could be interacting with the object's protoplanetary disk (if it has one). But if this active magnetic region is long-lasting and representative of its global magnetic field, LSR J1835+3259 is way more "star-like" than we give brown dwarfs credit for.

So rather than calling brown dwarfs "failed stars," perhaps we should call them overachieving planets or magneto-dwarfs.


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