New Discovery: Brown Dwarf Gliese 229B is Actually Two in a Binary System
In 1995, astronomers confirmed the first discovery of a brown dwarf, a celestial object too massive to be a planet yet too small to ignite as a star. However, recent studies have revealed that this original discovery was incomplete. What was thought to be a single brown dwarf, named Gliese 229B, is actually two brown dwarfs orbiting each other while circling a small star.
These findings, published in two new studies using telescopes in Chile and Hawaii, show that the brown dwarfs, now renamed Gliese 229Ba and Gliese 229Bb, are gravitationally bound in a binary system, a phenomenon commonly observed in stars but rare among brown dwarfs.
Details of the New Discovery
The two brown dwarfs are located about 19 light-years from Earth in the constellation Lepus. They are incredibly close to each other, orbiting every 12 days at a distance only 16 times that between Earth and the Moon. Gliese 229Ba has a mass 38 times that of Jupiter, while Gliese 229Bb is 34 times Jupiter’s mass.
This discovery clears up some anomalies from the original 1995 findings, where the mass of Gliese 229B was measured at 71 times that of Jupiter. This mass would normally make the object much brighter, leading researchers to suspect something was off. The new observations reveal that the brightness and mass make sense now that two separate brown dwarfs have been identified.
What are Brown Dwarfs?
Brown dwarfs are objects that fall between planets and stars. According to Sam Whitebook, a Caltech graduate student and lead author of one of the studies, brown dwarfs are objects capable of burning deuterium (a heavy form of hydrogen), but not the common hydrogen that fuels stars. This places their mass between 13 and 81 times that of Jupiter. Since they lack the necessary mass to sustain hydrogen fusion like stars, brown dwarfs only glow faintly as they cool down over time.
Both brown dwarfs in this system orbit a red dwarf star, a small and dim star type that is about 60% the mass of the Sun. Despite being more massive than Jupiter, these brown dwarfs have smaller diameters due to their higher density.
Implications for Star and Planet Formation
The discovery of these two brown dwarfs in such an unusual configuration has raised new questions about the formation of brown dwarfs and the fuzzy boundary between planets and brown dwarfs. Jerry Xuan, a Caltech astronomer and lead author of the second study, pointed out that this discovery shows how complex star formation can be, producing unexpected results.
“We still don’t fully understand the formation of brown dwarfs and their relationship with giant planets,” Xuan explained. This finding underscores the messy nature of star formation and emphasizes the importance of remaining open to surprises in astronomy.
