Astronomers have made a surprising discovery about the first brown dwarf ever identified. New observations suggest the object is actually two brown dwarfs orbiting each other.
The American space agency NASA describes a brown dwarf as an object that “straddles the dividing line between stars and planets.”
Brown dwarfs form like stars. This means they can grow dense and hot enough to collapse under their own gravity. But they never grow dense or hot enough to begin the process of nuclear fusion needed to turn into a star, NASA said. Because of this, brown dwarfs are sometimes called failed stars.
Many brown dwarfs are similar to gas giant planets and weigh just a few times more than the mass of Jupiter. Others can be much larger.
The first brown dwarf was discovered in 1995 by researchers from the California Institute of Technology (Caltech). The discovery was made with the help of the institute’s Palomar Observatory near San Diego, California.
But after many years of studying the object, known as Gliese 229B, scientists wondered why its brightness was less than expected for an object of its size.
New research now shows that the brown dwarf is actually two objects. The observations came from the Very Large Telescope, which sits in a desert area of northern Chile. Those observations showed that one of the brown dwarfs is about 38 times the mass of Jupiter, while the other is 34 times Jupiter’s mass.
In a statement, the researchers said data collected by the telescope suggests the two objects orbit each other every 12 days. That is less than half the time it takes for the moon to orbit the Earth. “The observed brightness levels of the pair match what is expected for two small dim brown dwarfs in this mass range,” the statement added.
The two brown dwarfs are gravitationally linked to each other in what is known as a binary system. Such a situation is commonly observed among stars but is rare for brown dwarfs.
After the new discovery, the two objects were given new names – Gliese 229Ba and Gliese 229Bb. The brown dwarfs are believed to orbit a star called a red dwarf. The two sit about 19 light-years away from our solar system. A light-year is the distance light travels in one year – about 9.5 trillion kilometers.
The research was co-led by Jerry Xuan, a graduate student at Caltech. He said in a statement that Gliese 229B was always considered “the poster child” for a brown dwarf.
"And now we know we were wrong all along about the nature of the object,” he added. “It's not one but two. We just weren't able to probe separations this close until now."
Astronomers had identified brown dwarf pairs before, but never any that orbited each other so closely. The research results recently appeared in a study in the publication Nature.
The team that discovered Gliese 229B in 1995 included Rebecca Oppenheimer. At the time, she was a Caltech graduate student. She is now an astrophysicist at the American Museum of Natural History in New York City. She was also a member of the latest research team.
Oppenheimer said, “It shows you how weird the universe is, and how different solar systems are from our own.” She added that she sees the new finding as “the most exciting and fascinating discovery” in this area of astrophysics in many years.
Caltech’s Jerry Xuan said the discovery suggests there might be other brown dwarfs closely orbiting each other. He added that he hopes the latest finding can lead to a greater understanding of brown dwarf development.
"We still don't really know how different brown dwarfs form, and what the transition between a giant planet and a brown dwarf is,” Xuan said.
He added, “This goes to show how complex and messy the star formation process is. We should always be open to surprises."
I’m Bryan Lynn.
