A team led by the Caltech Institute discovered that the brown dwarf is actually a close binary system consisting of two brown dwarfs orbiting against each other. This discovery provides a new perspective on brown dwarf binary systems and raises new questions about their formation and distribution in space.

Discovery of Gliese 229B: The Brown Dwarf Mystery

Hundreds of papers have been written about Gliese 229B, the first known brown dwarf, since its discovery in 1995 by Caltech researchers at the institute’s Palomar Observatory. But this sphere remains a mystery: given its considerable mass, it is an extremely dim light. As a general rule, brown dwarfs, which are celestial bodies heavier than gas giants like Jupiter but lighter than stars, should emit much more light at that mass. Measurements showed that Gliese 229B is about 70 times the mass of Jupiter, but its luminosity does not correspond to this weight.

Recently this mystery was solved by a group of international astronomers led by the California Institute of Technology. They found that what was thought to be a single brown dwarf was actually two brown dwarfs with masses about 38 and 34 times the mass of Jupiter, orbiting closely together and orbiting each other every 12 days. The observed brightness matches the expected brightness for two such small, dim brown dwarfs, solving the long-standing mystery of Gliese 229B’s dimness.

Discovery and Results

“Gliese 229B was thought to be the poster brown dwarf,” says graduate student Jerry W. Xuan, working with Dimitri Mavet, the David Morrisroe Professor of Astronomy. “And now we know that we were wrong all along about the nature of the object. Not one, not two. We haven’t been able to examine divorce this closely until now.” Xuan is the lead author of a new study published today (October 16) that reports the findings in the journal Science. Nature. A separate independent study Astrophysics Journal Letters The study, led by Caltech graduate student Sam Whitebook and astronomer Tim Brandt of the Space Telescope Science Institute in Baltimore, also concluded that Gliese 229B is a double brown dwarf.

The discovery raises new questions about how closely related brown dwarf binaries like this are and suggests that similar brown dwarf binaries, or even exoplanet binaries, may be waiting to be discovered. (An exoplanet is a planet that orbits a star other than our Sun.)

“This discovery that Gliese 229B is a binary system not only resolves the final discrepancy between its mass and luminosity, but also greatly improves our understanding of brown dwarfs that lie on the line between stars and giant planets,” says Mavet, also a senior. researcher. scientist at JPL, which is managed by NASA’s California Institute of Technology.

Historical significance of Gliese 229B

Gliese 229B was discovered in 1995 by a Caltech team that included Rebecca Oppenheimer, a graduate student at Caltech; Sri Kulkarni, George Ellery Hale Professor of Astronomy and Planetary Science; Kate Matthews, an instrumentation specialist at the Cal Institute of Technology; and other colleagues. Astronomers using the Palomar Observatory found that Gliese 229B’s atmosphere contains methane, a phenomenon typical of gas giants like Jupiter, not stars. This finding marked the first confirmed detection of a class of cool star-like objects called brown dwarfs (the missing link between planets and stars), theorized nearly 30 years ago.

“It was exciting to see the first object smaller than a star orbiting another sun,” said Oppenheimer, co-author of the new study and an astrophysicist at the American Museum of Natural History. “Then a cottage industry of people searching for similar oddities began, but it remained a secret for decades.”

The mysterious dimness of Gliese 229B

In fact, almost 30 years after its discovery and hundreds of observations, Gliese 229B still surprises astronomers with its unexpected faintness. Scientists suspected that Gliese 229B might be a twin, but Xuan says “the two brown dwarfs would have to be very close together to escape astronomers’ attention for 30 years.”

The team used two different instruments to separate Gliese 229B into two objects; both of these were mounted on the European Southern Observatory’s Very Large Telescope in Chile. They used the GRAVITY instrument, an interferometer that combines light from four different telescopes, to spatially split the body in half, and used the CRIRES+ (CRyogenic high-resolution Infrared Echelle Spectrograph) instrument to detect the different spectral signatures of the two objects. The second method involved measuring the motion (or Doppler shift) of molecules in the atmospheres of brown dwarfs; This showed that as the pair revolved around each other, one object was pointing towards us on Earth and the other was pointing in the opposite direction.

“It’s great to see a new development after almost 30 years,” says Kulkarni, who is not the author of the current paper. “Now these two are fascinating again.”

Vortex Space Dance: Orbital Features

These five months of observations revealed that the brown dwarf duo, now called Gliese 229Ba and Gliese 229Bb, orbit each other every 12 days, at a distance of only 16 times the distance between the Earth and the Moon. Together, the pair orbit an M-dwarf star (a smaller, redder star than our Sun) every 250 years.

“These two worlds orbiting each other are actually smaller in radius than Jupiter. “If something similar existed in our solar system, they would look pretty weird in the night sky,” says Oppenheimer. “This is the most exciting and exciting discovery in substellar astrophysics in decades.”

The secret of their formation

How this pair of spinning cosmic balls came to be is still a mystery. Some theories suggest that brown dwarf binaries may form in rotating disks of material surrounding a forming star. The disk will break apart into two brown dwarf seeds and be gravitationally bound together after a close encounter. It remains to be determined whether these mechanisms for the formation of planetary pairs around other stars would work.

Future Study of Brown Dwarf Binary Systems

In the future, the team wants to investigate binary brown dwarf systems in larger orbits with instruments such as the Keck Planet Imager and Characterizer (KPIC), developed by a team led by Mavet at the WM Keck Observatory in Hawaii. It is being built at Caltech and other laboratories by a team led by Mavet, alongside the Keck Observatory’s High Resolution Infrared Spectrograph for Characterization of Exoplanets (HISPEC).

“The fact that the first known brown dwarf companion is a double suggests that we will be looking for more,” says Xuan.