The artwork shows a pair of objects called brown dwarfs, named Gliese 229Ba and Gliese 229Bb, located about 19 light-years from our solar system. |Image credit: K. Miller, R. Hurt (Caltech/IPAC)/Reuters
In 1995, astronomers first confirmed the discovery of a brown dwarf, too small for a star and too large for a planet—a bit like an intermediate celestial body. But it turns out that’s not the whole story.
Researchers have now taken a second look at the brown dwarf and discovered that it is not actually one brown dwarf, but two brown dwarfs orbiting a small star surprisingly close to each other. Two new studies using telescopes in Chile and Hawaii document this.
The two brown dwarfs are gravitationally locked to each other in a so-called binary system, a common arrangement among stars. Therefore, the brown dwarfs named Gliese 229B thirty years ago are now identified as Gliese 229Ba, which is 38 times as massive as Jupiter, the largest planet in the solar system, and Gliese 229Bb, which is 34 times as massive as Jupiter.
They are located 19 light-years from our solar system – quite close in cosmic terms – in the constellation Lepus. A light year is the distance that light travels in one year, or 5.9 trillion miles (9.5 trillion kilometers).
Binary brown dwarfs are very rare. The two planets orbit each other every 12 days at a distance only 16 times the distance between the Earth and the Moon. Only one other pair of brown dwarfs is known to orbit as close as this pair.
Brown dwarfs are neither stars nor planets, but something in between. They can be thought of as stars that want to be stars, but do not achieve the mass required to ignite nuclear fusion in their cores like stars during their formation stages. But they are larger than the largest planets.
“Brown dwarfs are objects that fill the gap between planets and stars. They are formally defined as objects that can burn heavy hydrogen (called deuterium), but not the most common basic form of hydrogen,” Caltech Physics, Mathematics and Sam Whitebook, a graduate student in the Department of Astronomy and lead author of a paper.
“In practical terms, this means that they are about 13 to 81 times the mass of Jupiter. Because they cannot fuse hydrogen, they cannot ignite the fusion channels that power most stars. This causes them to emit only faint light as they cool. of light,” Whitebook said.
1995 was a big year for astronomers, with the announcement of the discovery of the first planet outside our solar system – an exoplanet. Before the discovery of Gliese 229B, the existence of brown dwarfs was only hypothesized. But there are anomalies in Gliese 229B, especially since its mass was measured to be about 71 times that of Jupiter.
“It doesn’t make sense, because an object of this mass would be much brighter than Gliese 229B,” said Jerry Xu, an astronomer at the California Institute of Technology and lead author of a study published in the journal Nature. “Indeed, some models predicted that objects with masses greater than 70 Jupiter masses would fuse hydrogen and become stars, but that clearly did not happen here.”
The new observations were able to identify two separate brown dwarfs. They orbit a common type of star called a red dwarf, which has about six-tenths the mass of the Sun. Although both brown dwarfs are more massive than Jupiter, their diameters are actually smaller than those of the gas giants because they are denser.
“We still don’t know how different brown dwarfs form and what the transition between giant planets and brown dwarfs is. The boundaries are blurry,” Xuan said. “This discovery also shows us that brown dwarfs can have strange structures that we didn’t expect. This goes to show how complex and chaotic the star formation process is. We should always be open to surprises.
Published – October 19, 2024 5:47 pm (IST)
