Astronomers Discover Widest Separation of Brown Dwarf Pair to Date

An artist’s rendition of a binary system of brown dwarfs like cwise j014611.20-050850.0ab.
Credit: William Pendrill

Maunakea, Hawaiʻi – A team of astronomers has discovered a rare pair of brown dwarfs that has the widest separation of any brown dwarf binary system found to date.

“Because of their small size, brown dwarf binary systems are usually very close together,” said Emma Softich, an undergraduate astrophysics student at the Arizona State University (ASU) School of Earth and Space Exploration and lead author of the study. “Finding such a widely separated pair is very exciting.”

The gravitational force between a pair of brown dwarfs is lower than for a pair of stars with the same separation, so wide brown dwarf binaries are more likely to break up over time, making this pair of brown dwarfs an exceptional find.

The study, which is based on observations the University of California San Diego (UC San Diego) Cool Star Lab conducted with W. M. Keck Observatory on Maunakea, Hawaiʻi Island, is published in today’s issue of The Astrophysical Journal Letters.                           

Using Keck Observatory’s Near-Infrared Echellette Spectrometer, or NIRES instrument,  members of the UC San Diego Cool Star Lab, including Physics Professor Adam Burgasser and graduate students Christian Aganze and Dino Hsu, obtained infrared spectra of the brown dwarf binary system, called CWISE J014611.20-050850.0AB. The data revealed the two brown dwarfs are about 12 billion miles apart, or three times the separation of Pluto from the Sun. This distance confirms the unusual brown dwarf couple breaks the record for having the widest separation from each other.

“Keck’s exceptional sensitivity in the infrared with this instrument was critical for our measurements,” said co-author Burgasser, who leads the Cool Star Lab. “The secondary brown dwarf of this system is exceptionally faint, but with Keck we were able to obtain good enough spectral data to classify both sources and identify them as members of a rare class of blue L dwarfs.”

“Wide, low-mass systems like CWISE J014611.20-050850.0AB are usually disrupted early on in their lifetimes, so the fact that this one has survived until now is pretty remarkable,” said co-author Adam Schneider of the U.S. Naval Observatory, Flagstaff Station and George Mason University.

WISE (left) and the Dark Energy Survey Collaboration (DES) (right) images of CWISE J0146-0508AB. In the lower-resolution WISE image, the pair are blended into a single point-source, while two distinct entities are visible in the higher-resolution DES image. The reddish hue of both objects in the DES image shows that they emit much of their light in the infrared, a trait typical of brown dwarfs. Credit: WISE/DES/Softich et al.

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

Many brown dwarfs have been discovered with data from NASA’s Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, which solicits help from the public to search the WISE image data bank to find brown dwarfs and low-mass stars, some of the Sun’s nearest neighbors.

For this study, the researchers inspected images of Backyard Worlds discoveries, where companion brown dwarfs may have been overlooked. In doing so, they discovered the rare CWISE J014611.20 050850.0AB brown dwarf binary system.

Softich went through about 3,000 brown dwarfs from Backyard Worlds one by one and compared the WISE images to other survey images, looking for evidence of a brown dwarf companion to the original target. The team then used data from the Dark Energy Survey (DES) to confirm that it was indeed a brown dwarf pair.

They then used Keck Observatory’s NIRES to confirm the brown dwarfs have spectral types L4 and L8, and that they are at an estimated distance of about 40 parsecs, or 130.4 light-years from Earth, with a projected separation of 129 astronomical units, or 129 times the distance between the Sun and the Earth.

The team hopes this discovery will allow astronomers the chance to study brown dwarf binary systems and to develop models and procedures that will help in recognizing more of them in the future.

“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,” said co-author Jennifer Patience, Softich’s adviser at ASU.

Source: W. M. Keck Observatory

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About NIRES

The Near Infrared Echellette Spectrograph (NIRES) is a prism cross-dispersed near-infrared spectrograph built at the California Institute of Technology by a team led by Chief Instrument Scientist Keith Matthews and Prof. Tom Soifer. Commissioned in 2018, NIRES covers a large wavelength range at moderate spectral resolution for use on the Keck II telescope and observes extremely faint red objects found with the Spitzer and WISE infrared space telescopes, as well as brown dwarfs, high-redshift galaxies, and quasars. Support for this technology was generously provided by the Mt. Cuba Astronomical Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaiʻi feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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Astronomers Catch Rare Eclipse Of A Double Brown Dwarf System

An artist's view of one of de Speculoos Telescopes, with the eclipsing binary brown dwarf in the sky. The third red dot is a third nearby brown dwarf, whick is also part of the same system. The book on the side shows the data that led to discovery. On the left page is the eclipse captured by Speculoos while the right page show the data form Keck Observatory and VLT. The illustration's copyright is University of Birminghan/Amanda J. Smith

Maunakea, Hawaii – Astronomers working on “first light” data from a newly commissioned telescope in Chile made a chance discovery that led to the identification of a rare eclipse of two brown dwarfs. The result, which includes data taken from W. M. Keck Observatory on Maunakea in Hawaii to help confirm the discovery, published today in the journal Nature Astronomy.

Sometimes called “failed stars,” brown dwarfs occupy a grey zone between stars and giant planets. They are unable to sustain the fusion of hydrogen into helium, a process that powers the light from normal stars like the sun; yet they appear to form like stars, only with less mass. They provide a critical link in scientists’ understanding of star and planet formation.

The chance discovery was led by an international team of researchers, including scientists at UC San Diego, working on a project called SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars), which aims to find planets orbiting the smallest stars, including brown dwarfs. SPECULOOS finds planets by detecting periodic dips in a star’s brightness as a planet passes in front of it, an event called a planetary transit. Astronomers predict that the smallest stars and brown dwarfs could host large populations of close-in, potentially habitable rocky planets, like the famous seven-planet system TRAPPIST-1 that was discovered in 2017 by members of the same team.

“This is a great example of scientific serendipity,” explained Adam Burgasser, professor of physics at UC San Diego and co-leading author on the study. “While searching for planets, we found an eclipsing brown dwarf binary, a system that is uniquely suited for studying the fundamental physics of these faint celestial objects.”

Soon after the construction of the first SPECULOOS telescopes in Chile, and during early testing observations, the team targeted the brown dwarf “2MASSW J1510478-281817,” also known as 2M1510, in the constellation Libra. In this case, the SPECULOOS observations picked up a distinct signal that led the researchers to speculate that 2M1510 might be two brown dwarfs instead of one, in orbit around each other.

“Among the first test observations we performed, we turned one of our telescopes to a known brown dwarf. But suddenly the object appeared to get dimmer for about 90 minutes, which indicated an eclipse just took place,” reported Michaël Gillon, principal investigator of the SPECULOOS project.

Artem Burdanov, a postdoctoral researcher at Massachusetts Institute of Technology and co-author on the study concurred, adding, “We rapidly realized that we were probably looking at two eclipsing brown dwarfs, one passing in front of the other, a configuration which is much rarer than planetary systems.”

The researchers were able to confirm their hypothesis using two powerful telescopes – the 10-meter Keck II telescope and the 8-meter Very Large Telescope (VLT) on Cerro Paranal in Chile, the same site as the SPECULOOS telescopes. Keck Observatory and VLT are each equipped with sensitive spectrometers (the Near-Infrared Spectrograph, or NIRSPEC, at Keck Observatory and VLT’s UV-Visual Échelle Spectrograph, or UVES) that can measure the velocities of celestial objects. In the case of 2M1510, the astronomers detected the velocities of both brown dwarfs as they orbit one another.

“From the very first spectrum we obtained, we could tell we had an exciting binary discovery,” said Burgasser, who led the spectroscopic analysis with current and former graduate students at UC San Diego’s Cool Star Lab. “It was thrilling to see the absorption lines move back and forth in perfect synchronicity, which allowed us to measure the mass of the binary.”

The detection of an eclipsing brown dwarf binary is extremely rare because the system needs to be precisely aligned with our line-of-sight to move in front of each other. Only one other such system has been identified to date. These systems allow astronomers to measure both the radii and masses of the brown dwarfs directly. 2M1510 is also unique in that it is among the few brown dwarfs that have a known age, due to its membership in a nearby cluster of young stars called the Argus moving group. The eclipsing binary is also part of a brown dwarf triple system—another rarity—with a third component orbiting at a much wider separation.

“Collecting a combination of mass, radius, and age is really rare for a star, let alone for a brown dwarf,” explained Amaury Triaud, Birmingham Fellow at the University of Birmingham in the UK who was the primary author of the study. “Usually one or more of these measurements is missing. By drawing all these elements together, we were able to verify theoretical models for how brown dwarfs cool, models which are over 30 years old. We found the models match remarkably well with the observations, a testament to human ingenuity.”

Source: W. M. Keck Observatory/News

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About NIRSPEC

The Near-Infrared Spectrograph (NIRSPEC) is a unique, cross-dispersed echelle spectrograph that captures spectra of objects over a large range of infrared wavelengths at high spectral resolution. Built at the UCLA Infrared Laboratory by a team led by Prof. Ian McLean, the instrument is used for radial velocity studies of cool stars, abundance measurements of stars and their environs, planetary science, and many other scientific programs. A second mode provides low spectral resolution but high sensitivity and is popular for studies of distant galaxies and very cool low-mass stars. NIRSPEC can also be used with Keck II’s adaptive optics (AO)system to combine the powers of the high spatial resolution of AO with the high spectral resolution of NIRSPEC. Support for this project was provided by the Heising-Simons Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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