Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence

• Published in: Nature (London) Vol. 523; no. 7562; pp. 568 - 571
• Main Authors: Hallinan, G., Littlefair, S. P., Cotter, G., Bourke, S., Harding, L. K., Pineda, J. S., Butler, R. P., Golden, A., Basri, G., Doyle, J. G., Kao, M. M., Berdyugina, S. V., Kuznetsov, A., Rupen, M. P., Antonova, A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 30.07.2015; Nature Publishing Group
• Subjects: 639/33/34/867; 639/33/525/868; 639/33/525/869; Atmosphere; Auroras; Dwarf stars; Emissions; Humanities and Social Sciences; letter; Magnetic fields; Magnetism; Magnetosphere; multidisciplinary; Observations; Science; Spectrum allocation; Stars; Upper atmosphere; United States; United Kingdom; Ireland
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature14619

Radio and optical spectroscopic observations of a brown dwarf reveal auroral emissions powered by magnetospheric currents, showing that aurorae may be a signature of magnetospheres much larger than those observed in our Solar System. Planet-like aurorae on a dwarf star Radio and optical spectroscopic observations of a dwarf star reveal auroral emissions powered by magnetospheric currents, the first confirmed detection of a planet-like aurora from a body outside our Solar System. The Sun-like coronal activity thought to dominate in main sequence stars is powered by processes that occur in their lower atmospheres, whereas on this dwarf star — at the boundary between stars and brown dwarfs — the aurorae are powered by processes originating much further out in the magnetosphere and coupled to the lower atmosphere. Aurorae are detected from all the magnetized planets in our Solar System, including Earth 1 . They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons 2 , as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere 3 . Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs.