Magnetospheric plasma sources around the ultra-cool dwarf LSR J1835+3259

Star system: 2MASS 1835+3259 | Distance from the Sun: 18.6 light years

Radio waves emitted by ultra-cool dwarf stars suggest these objects possess radiation belts similar to those found around Jupiter. These belts consist of plasma, a state of matter containing charged particles, trapped within the star's magnetic field. This study investigates the origin of this plasma for the ultra-cool dwarf LSR J1835+3259 by modeling potential sources, such as escaping atmospheric ions or material from a volcanic moon.

The research evaluates two main mechanisms. First, an ionospheric outflow, where charged particles escape the star’s atmosphere, could provide the necessary plasma if the star's upper atmosphere has a low electrical conductivity. Conductance measures how easily a material allows electricity to flow; here, it limits how many ions can escape. This model requires specific conditions to sustain the observed radio emission.

Alternatively, a tidally-heated volcanic moon, similar in size to Jupiter’s moon Io, is considered. Such a moon would release material into the star's magnetosphere. This scenario functions effectively if the moon orbits within 10 stellar radii and maintains a slightly elliptical orbit due to the gravity of other planets in the system. This volcanic moon hypothesis aligns with observations showing that ultra-cool dwarfs with companions are more likely to emit radio waves.

Key findings
- LSR J1835+3259 possesses radio-emitting magnetospheric structures similar to Jupiter's radiation belts.
- Ionospheric outflow at a rate of 100,000 kilograms per second is a possible source of magnetospheric plasma.
- A volcanic moon similar to Io is a viable plasma source if it orbits within 10 stellar radii.
- Orbital eccentricity for a potential moon is likely maintained by gravitational interactions with other planets.
- The volcanic moon scenario explains why ultra-cool dwarfs with companions are more frequent radio emitters.

Scientific study

Volcanic Satellites and Ion Escape in the Magnetospheres of Ultra-Cool and Brown Dwarf Stars (external link)