Named UPM J1040-3551 AabBab, the newly-discovered quadruple star system consists of a pair of cold brown dwarfs and a pair of young red dwarfs.
An artist’s impression of the UPM J1040-3551 system against the backdrop of the Milky Way as observed by ESA’s Gaia satellite; on the left, UPM J1040-3551 Aa & Ab appears as a distant bright orange dot, with an inset revealing these two M-type stars in orbit; on the right, in the foreground, a pair of cold brown dwarfs — UPM J1040-3551 Ba & Bb — orbit each other for a period of decades while collectively circling UPM J1040-3551 Aab in a vast orbit that takes over 100,000 years to complete. Image credit: Jiaxin Zhong / Zenghua Zhang.
UPM J1040-3551 AabBab is located approximately 82 light-years away in the constellation of Antlia.
In this system, Aab refers to the brighter stellar pair Aa and Ab, while Bab refers to the fainter substellar pair Ba and Bb.
“What makes this discovery particularly exciting is the hierarchical nature of the system, which is required for its orbit to remain stable over a long time period,” said Nanjing University’s Professor Zenghua Zhang.
“These two pairs of objects are orbiting each other separately for periods of decades, while the pairs are also orbiting a common center of mass over a period of more than 100,000 years.”
The two pairs are separated by 1,656 AU (astronomical units), where 1 AU equals the Earth-Sun distance.
The brighter pair, UPM J1040-3551 Aab, consists of two nearly equal-mass red dwarf stars, which appear orange in color when observed in visible wavelengths.
These stars have temperatures of 3,200 K (about 2,900 degrees Celsius) and masses of about 17% that of the Sun.
With a visual magnitude of 14.6, the pair is approximately 100,000 times fainter than Polaris (the North Star) in visible wavelengths.
The fainter pair, UPM J1040-3551 Bab, comprises two much cooler brown dwarfs that emit virtually no visible light and appear roughly 1,000 times dimmer than the Aab pair when observed in near-infrared wavelengths, where they are most easily detected.
These brown dwarfs have a spectral type T and temperatures of 820 K (550 degrees Celsius) and 690 K (420 degrees Celsius), respectively.
“This is the first quadruple system ever discovered with a pair of T-type brown dwarfs orbiting two stars,” said Dr. MariCruz Gálvez-Ortiz, an astronomer at the Center for Astrobiology in Spain.
“The discovery provides a unique cosmic laboratory for studying these mysterious objects.”
“Brown dwarfs with wide stellar companions whose ages can be determined independently are invaluable at breaking this degeneracy as age benchmarks,” said University of Hertfordshire’s Professor Hugh Jones.
“UPM J1040-3551 is particularly valuable because H-alpha emission from the brighter pair indicates the system is relatively young, between 300 million and 2 billion years old.”
The team believes the brown dwarf pair could potentially be resolved with high-resolution imaging techniques in the future, enabling precise measurements of their orbital motion and dynamical masses.
“This system offers a dual benefit for brown dwarf science,” said University of California San Diego’s Professor Adam Burgasser.
“It can serve as an age benchmark to calibrate low-temperature atmosphere models, and as a mass benchmark to test evolutionary models if we can resolve the brown dwarf binary and track its orbit.”
“The discovery of the UPM J1040-3551 system represents a significant advancement in the understanding of these elusive objects and the diverse formation paths for stellar systems in the neighborhood of the Sun.”
The discovery is reported in a paper in the Monthly Notices of the Royal Astronomical Society.
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Z.H. Zhang et al. 2025. Benchmark brown dwarfs – I. A blue M2 + T5 wide binary and a probable young [M4 + M4] + [T7 + T8] hierarchical quadruple. MNRAS 542 (2): 656-668; doi: 10.1093/mnras/staf895
