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Evidence for a radiation belt around an ultracool dwarf

 

Ultracool dwarfs (UCDs) are low-mass stars and sub-stellar objects of spectral type later than M6 with some interesting characteristics at radio frequencies. In this work, we used the European VLBI Network (EVN) to observe the fast-rotating UCD LSR J1835+3259, at only 5.6885 ± 0.0015 pc (Gaia Collaboration et al. 2023). The observations revealed a detailed image of the first radiation belt detected beyond the Solar System.

Ultracool dwarf
Artistic impression of the ultracool dwarf LSR J1835+3259 (central object). Magnetic field,  radiation belt, and auroras are visible. Image credits: Illustration by Hugo Salais / Metazoa Studio.

As already known, our observations showed that the radio emission from LSR J1835+3259 is characterized by a quiescent, slowly varying component (gyrosynchrotron and/or synchrotron; Williams et al. 2015, Hughes et al. 2021) and sudden bursts of highly circularly polarised radio emission that have been interpreted as aurorae (Hallinan et al. 2015). However, and for the first time, the great sensitivity of the EVN allowed us to resolve the magnetosphere of the object when it was producing auroral emission, revealing a double-lobed structure strikingly similar to the well-known radiation belts of Earth and Jupiter.

 

LSR J1835+3259
Reconstructed radio images of LSR J1835+3259 using the European VLBI Network. The two spots correspond to the donut-like radiation belt seen edge-on. The contour plot represents powerful polarized light originating at the aurora, near the surface of the brown dwarf, located halfway between the radio components of the radiation belt. Image credits: Juan B Climent.

 

The similarity with Jupiter’s radiation belts is mostly morphological as the diameter of the magnetic structure around the ultracool dwarf is ten times larger than that of Jupiter, and millions of times more powerful.  The extraordinary results in LSR J1835+3259 show that the EVN is capable of mapping radiation belts in nearby objects, paving the way to future instruments, such as the Square Kilometre Array, that would extend these studies to smaller and more remote objects, including exoplanets where the knowledge of their magnetic environments is extremely important to calibrate the possibilities of hosting alien life.

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More information:

'Evidence for a radiation belt around a brown dwarf'. J. B. Climent, J. C. Guirado, M. Pérez-Torres, J. M. Marcaide, L. Peña-Moñino. https://www.science.org/doi/10.1126/science.adg6635  . DOI 10.48550/arXiv.2303.06453 

 

Contact:

Juan Bautista Climent

Universitat de València / Valencia International University

E-mail: j.bautista.climent@uv.es

Ph: 655 39 30 08

 

Jose Carlos Guirado

Universitat de València

E-mail: guirado@uv.es

Ph: 629 50 91 30