This artist’s illustration shows the Gliese 229 system, with a primary red dwarf in the background and two brown dwarfs orbiting each other in the foreground. Credits: K. Miller, R. Hurt (Caltech/IPAC)
In 1995, a parallel race was underway in astronomy: one to find the first planet beyond our solar system, and the other to find the first brown dwarf, a class of objects too heavy to be a planet, but less than the mass of a planet. star.
Astronomers ended up publishing the discovery of the first exoplanet around a Sun-like star – 51 Pegasi b – in early October of that year, and the announcement of the discovery of the brown dwarf, Gliese 229 B, in late November . Except now, it turns out they are I didn’t discover the first confirmed brown dwarf.
They found out two brown dwarfs.
In independent research published in Nature AND The letters from the astrophysics diaryastronomers have announced the true nature of Gliese 229 B and, in the process, have solved many mysteries about what is happening there.
Snuggled close to each other
Brown dwarfs form no differently than stars, except that brown dwarfs fail to reach a mass threshold to fuse hydrogen into helium. The limit varies depending on composition and other mitigating factors, but usually objects with a mass between 70 and 80 Jupiters have enough of what is needed to become a bona fide star.
That’s right around the estimated mass of Gliese 229 B, which orbits a red dwarf parent star that has about 60 percent the mass of the Sun. But despite the fact that Gliese 229 B appeared to be on the verge of becoming a star itself, it had not ignited and remained relatively cold.
“There’s basically this tension between the high mass of this object and the fact that it’s so faint and cold, which didn’t make sense, given our models of brown dwarfs,” Jerry W. Xuan, a Caltech graduate student and lead author of IL Nature paper, he says. “So people have speculated that it might be a binary brown dwarf and that might solve this problem.”
Gliese 229 B is located just 19 light-years from Earth. Xuan says this led the team to realize that since they had not detected a binary object after years of searching with both space missions and ground-based instruments, the two objects should have been very close to each other. The team used the GRAVITY interferometer, which can closely observe changes in an object’s path caused by invisible objects, and the CRIRES+ spectrograph, which breaks down an object’s light to identify its constituent molecules.
Although Gliese 229 B is not bright enough to shine like a star, it is still hot due to its formation and relatively young age, so the object can be imaged directly. (Hubble did this to confirm its detection in 1995.) That also means it could be studied closely to determine whether it wobbles due to an unseen companion, and if so, glean details about both objects.
And this was exactly the case: Gliese 229 B is composed of a brown dwarf of mass 38 Jupiter in a mutual orbit with a brown dwarf of mass 34 Jupiter, orbiting each other just 4 million miles (6 .4 million kilometers) away. It’s a very small distance, cosmically speaking. (For reference, the Sun is 93 million miles away on average [150,000 km] from Earth and the Moon is an average of 238,000 miles [383,000 km] from Earth.)
History of origin
Xuan says the brown dwarfs likely formed due to instabilities in the same disk of material that formed their parent star, Gliese 229 A, and therefore formed somewhat like stars themselves. But for some reason, each of the brown dwarfs formed distinctly from each other rather than as a small protostar. It may be that the ignition of Gliese 229 A prevented the objects from forming as one.
“The disk would have to be massive enough to contain enough mass for the two brown dwarfs, but if that were the case, then such a massive disk would probably be unstable to gravitational collapse, and that would mean it basically fragments into these smaller objects around us. the star,” says Xuan.
Xuan and colleagues are about to observe the weather on the James Webb Space Telescope, which will help them learn more about the pair of brown dwarfs, including directly measuring their radii. The details they gather could help us learn more about those who are now frontrunners two they confirmed brown dwarfs and provided insights into how these enigmatic objects form.
And it could open up an even wilder possibility within a system that already has a star, two brown dwarfs and evidence of a pair of Neptune-sized planets.
“So I would say it’s not a priority… and this is more hypothetical, but if we collect a lot of data on the orbit of the brown dwarf binary system, we could see if there’s any evidence that there’s something else around them, ” Xuan says. In other words, Xuan’s team may be able to discover whether two brown dwarfs orbiting each other, both orbiting a larger star, might have a small planet orbiting They, Also.
It would certainly be an interesting discovery.
