Arezki Amiri Published on November 2, 2024
Collected at: https://dailygalaxy.com/2024/11/mysterious-brown-dwarf-is-not-single-star/
Two independent studies have revealed groundbreaking insights about the brown dwarf Gliese 229 B, a discovery that reshapes our understanding of this celestial object. Both research teams concluded that Gliese 229 B is not a solitary brown dwarf but a binary system, comprised of two separate brown dwarfs. Their investigations employed advanced astronomical instruments in different ways, yet they arrived at remarkably similar findings.
The Puzzle of Brown Dwarfs
Brown dwarfs occupy an intriguing position between gas giants and true stars. Although massive, they lack the size needed to ignite nuclear fusion in their cores, instead glowing faintly from the heat of their formation. Their brightness correlates with mass, making Gliese 229 B‘s relatively dim appearance for its estimated mass a long-standing enigma.
Discovered in 1994, Gliese 229 B was the first confirmed brown dwarf, identified in orbit around a red dwarf star. Its atmosphere, rich in methane like Jupiter’s, made it a unique discovery, hinting at characteristics shared with massive exoplanets. However, astrometry and radial velocity studies suggested a mass of 71 Jupiter masses, sparking a mystery: such a massive object should be much brighter, challenging established brown dwarf models.
Xuan’s Investigation Using Advanced Instruments
To tackle this mass-brightness paradox, Jerry Xuan of Caltech led a team utilizing the European Southern Observatory’s Very Large Telescope (VLT) in Chile. They deployed two sophisticated tools:
- CRIRES+, a high-resolution infrared spectrograph that separates light from different objects with precision.
- GRAVITY, an interferometer combining light from four telescopes to achieve unprecedented spatial resolution.
Xuan explained, “CRIRES+ disentangles light by dispersing it at high spectral resolution, while GRAVITY interferes light from all four telescopes to capture fine spatial details.”
By merging these observations, the team discovered that Gliese 229 B is indeed two brown dwarfs—now named Gliese 229Ba and Gliese 229Bb—orbiting each other every 12 days at a separation of 16 Earth-Moon distances. Further spectral analysis indicated two distinct atmospheres, reinforcing the binary nature of the system.
Independent Confirmation from Keck Observatory
Simultaneously, a team led by Samuel Whitebrook from the University of California, Santa Barbara, used the Near-Infrared Spectrograph (NIRSPEC) at the Keck Observatory in Hawaii. NIRSPEC’s extreme resolution allowed them to detect time-varying spectral shifts, hinting at an unseen gravitational partner. These previously unnoticed frequency variations provided compelling evidence for the binary structure of Gliese 229 B.
Both studies, arriving at nearly identical conclusions, suggest a hidden binary system whose combined mass was misleadingly high when assumed to be a single object. Crucially, Gliese 229Ba and Gliese 229Bb are both significantly dimmer compared to a single brown dwarf of equal mass. This explains why Gliese 229 B has appeared so dim despite its estimated mass.
Broader Implications for Astronomy
The revelations extend beyond Gliese 229 B. Xuan’s team believes that similar brown dwarf binaries likely exist around other stars, and perhaps even among giant exoplanets like Jupiter. These systems could become key targets for future observations, further unraveling the complexities of star and planet formation. As Xuan remarked, “Our findings show how complex and messy the star formation process is. We should always be open to surprises, given the vast diversity in the Milky Way.”
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