Posted by Astronomers may have detected an unusual planetary-mass object orbiting a brown dwarf, although researchers are stopping short of calling it the first confirmed exomoon.
The candidate was discussed by Universidad Diego Portales PhD student Kevin Hoy in a recent SETI Live conversation with SETI Institute scientist Franck Marchis. Hoy’s team is confident that the observed signal represents a real object, but its classification remains uncertain. For this reason, the researchers use the broader term “exosatellite.”
The object appears to orbit CD-35 2722 B, a brown dwarf occupying the mass range between giant planets and low-mass stars. The candidate itself may have roughly Jupiter’s mass and appears to follow an eccentric orbit. Researchers detected it using radial-velocity measurements from CRIRES+, a high-resolution infrared spectrograph on the Very Large Telescope. Instead of measuring a star’s motion caused by a planet, the team tracked subtle changes in the brown dwarf’s velocity caused by an unseen companion.
The initial dataset covered about two years and revealed a repeating signal. When researchers fitted an orbital model, it predicted where future measurements should fall. New observations subsequently matched those predictions closely, strengthening the case for an orbiting object.
Hoy estimates his confidence in the detection at about 90 percent. One possible alternative is that atmospheric or surface activity on the brown dwarf could imitate a radial-velocity signal. However, its expected rotation period is no more than about 12 hours, while the detected signal repeats over approximately 170 days, making that explanation difficult. The system’s formation is also puzzling. One possibility is gravitational instability in a massive disk, but the highly eccentric orbits are challenging to explain. A two-satellite model fits the data slightly better, although simulations suggest such a configuration would usually become unstable within only a few years.
Future observations, particularly with next-generation telescopes such as the Extremely Large Telescope, could clarify the object’s nature and help determine how common satellite systems around brown dwarfs may be.
For more details, read the full article by SETI Institute and listen to the Live conversation.
