Rare Pair Of Brown Dwarfs Discovered. Know Why The Binary System Is Special

A team of astronomers has recently discovered a rare pair of brown dwarfs. The study was published in The Astrophysical Journal Letters.

Representative image of a brown dwarf | Photo: NASA

New Delhi: A team of astronomers has recently discovered a rare pair of brown dwarfs. The pair is special because it has the widest separation of any brown dwarf binary system found to date.

The study, based on observations the University of California San Diego Cool Star Lab conducted with WM Keck Observatory on Mauna Kea, Hawaii Island, was recently published in The Astrophysical Journal Letters.

What Are Brown Dwarfs?

Brown dwarfs are celestial objects that are smaller than a normal star, and are not massive enough to sustain nuclear fusion and shine like normal stars. 

According to NASA, brown dwarfs are failed stars about the size of Jupiter, with a much larger mass but not quite enough to become stars. Brown dwarfs, like the Sun and Jupiter, are composed mainly of hydrogen gas. They have no internal energy source and emit no visible light, unlike the Sun. 

However, brown dwarfs are hot enough to radiate energy, the WM Keck Observatory said on its website.

Astronomers, using data from NASA's Wide-field Infrared Survey Explorer (WISE), have discovered several brown dwarfs, as part of the ‘Backyard Worlds: Planet 9’ citizen science project. 

Finding Such A Pair Is “Very Exciting”

Emma Softich, a student at the Arizona State University School of Earth and Space Exploration and lead author of the study, said that brown dwarf binary systems are usually very close together, because of their small size, according to a statement issued by WM Keck Observatory. She said that finding such a widely separated pair is "very exciting".

Wide brown dwarf binaries are more likely to break up over time, because the gravitational force between a pair of brown dwarfs is lower than for a pair of stars with the same separation. This makes the recently discovered pair of brown dwarfs an exceptional find, the study said.

Members of the UC San Diego Cool Star Lab, using Keck Observatory's Near-Infrared Echellette Spectrometer, or NIRES instrument, obtained infrared spectra of the brown dwarf binary system, the study said. NIRES is designed to study explosive, deep sky phenomena such as supernovae and gamma ray bursts, and to find the faintest and most violent objects in the universe. 

What Is Special About The Brown Dwarfs?

According to the study, the two brown dwarfs are about 12 billion miles apart, or three times the separation of Pluto from the Sun. This distance confirms that the unusual brown dwarf couple breaks the record for having the widest separation from each other, the study said.

Adam Burgasser, who co-authored the study, said that Keck's exceptional sensitivity in the infrared with this instrument was critical for the researchers' measurements. He further said that the secondary brown dwarf of this system is exceptionally faint. But with Keck, the researchers were able to obtain good enough spectral to classify both sources and identify them as members of a rare class of blue L dwarfs, Adam said. L dwarfs are cool, faint stars with surface temperatures in the range of 2200 to 1300 Kelvin.

Adam Schneider, another co-author of the study, said that wide, low-mass systems like the newly discovered system are usually disrupted early on in their lifetimes. Therefore, the fact that this one survived until now is pretty remarkable, he said.

The researchers inspected images of Backyard Words discoveries in order to conduct this study. This is how they discovered the rare brown dwarf binary system, according to the study.

Softich searched through about 3,000 brown dwarfs from Backyard Worlds, one by one. She compared the WISE images to other survey images, in order to find evidence of a brown dwarf companion to the original target, the study said.

Then, the researchers used data from the Dark Energy Survey (DES) to confirm that it was indeed a brown dwarf pair.

After this, the team used Keck Observatory's NIRES to confirm that the brown dwarfs are at an estimated distance of about 40 parsecs, or 130.4 light-years away from Earth. The two brown dwarfs have a projected separation of 129 astronomical units, or 129 times the distance between the Sun and the Earth, the study said.

Jennifer Patience, another co-author of the study, said that binary systems are used to calibrate many relations in astronomy, and this newly discovered pair of brown dwarfs will present an important test of brown dwarf formation and evolution models.