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By combining the power of ground-based and space-based telescopes, astronomers have discovered a new brown dwarf—a type of object that lies between a star and a planet—orbiting a small star about 55 light-years from Earth. In addition, infrared observations revealed variations in its brightness, suggesting that clouds and storms may be forming and moving within the brown dwarf's atmosphere.

In our Milky Way galaxy, the most common type of star is the small, cool star known as an M dwarf, or red dwarf. They make up more than half of all the stars in our galaxy. Because M dwarfs are intrinsically faint, it has been difficult to determine how many of them have planets or brown dwarfs as companions. Brown dwarfs are too light to shine like normal stars yet are heavier than planets, so they bridge the gap between the two. Understanding how frequently such companions exist, and what masses they have, is essential for learning how stars and planets form and evolve.

An international research team led by the Astrobiology Center, California State University Northridge, and Johns Hopkins University has now discovered a brown dwarf companion orbiting a nearby M dwarf LSPM J1446+4633 (hereafter J1446), located about 55 light-years from Earth (fig. 1).

The companion, J1446B, has a mass of about 60 times that of Jupiter and orbits its host star at a distance 4.3 times the Earth–sun separation, completing one orbit in about 20 years. In addition, near-infrared observations revealed brightness variations of about 30%, indicating possible cloud activity or atmospheric circulation on the brown dwarf.

The study, "Direct Imaging Explorations for Companions from the Subaru/IRD Strategic Program II; Discovery of a Brown-dwarf Companion around a nearby Mid-M-dwarf LSPM J1446+4633," is in The Astronomical Journal.

"Studying the weather on these distant objects not only helps us to understand how their atmospheres form, but also informs our larger search for life planets beyond the solar system," says Taichi Uyama, researcher with the Astrobiology Center of Japan and lead author of the study.

The key to this discovery was the combination of three complementary observation techniques: (1) precise radial velocity measurements using InfraRed Doppler (IRD) on the Subaru Telescope, (2) direct imaging with the W. M. Keck Observatory, and (3) astrometric measurements of the host star's motion with the Gaia spacecraft.

By analyzing all three datasets together, the team accurately determined the mass and orbit of the companion (fig. 2). In particular, the Subaru Telescope's six years of data from its strategic program (IRD-SSP) were crucial. Radial velocity data alone cannot break the degeneracy between mass and orbital inclination, but adding direct imaging and Gaia astrometry resolves this ambiguity.

Previous studies have demonstrated the power of combining Hipparcos and Gaia astrometry with direct imaging to detect and characterize companions. However, Hipparcos was unable to measure the positions of faint red dwarfs like J1446. This study is the first to apply Gaia-only data to such a system, successfully constraining the orbit and dynamical mass of a brown dwarf companion.

This discovery provides a critical benchmark for testing brown dwarf formation scenarios and atmospheric models. Future observations may even allow researchers to map the weather patterns of this intriguing object. This result highlights the power of combining ground-based and space-based telescopes to uncover hidden worlds beyond our solar system.