Ultracool Stellar Magnetism


"Ultracool dwarfs" are the very smallest, coldest stars in the Universe. Some of them aren't even massive enough to power themselves with hydrogen fusion in their cores, making them technically "brown dwarfs" rather than stars, destined to slowly cool off for the rest of the Universe's lifetime. These stars are not capable of generating magnetic fields the same way that our Sun does, and conventional wisdom used to be that they would display only weak signs of magnetism.

That changed in 2001 when our group observed the brown dwarf LP 944-20 and discovered bursts of radio emission, a telltale sign of vigorous magnetic activity. Since then, we have conducted a long-running campaign to search for more magnetically-active ultracool dwarfs and understand how they work, using a wide range of observatories including the Very Large Array, Chandra , Swift, and Magellan. Our work has revealed many puzzling effects and helped show that in many cases these objects have emission more reminiscent of Earth's aurora than the Sun's flares. Not only are the basic physics of these processes poorly-understood, but they also impact our understanding of the stellar formation and evolution, weather and chemistry in these stars' atmospheres, and the habitability of exoplanets.


Peter K. G. Williams, Edo Berger