Rare quadruple star system could help unlock long-standing mysteries of how stars and planets form

The system, known as UPM J1040−3551 AabBab, is located around 82 light-years from Earth in the constellation Antlia.

It consists of a pair of cold brown dwarfs orbiting a pair of young red dwarf stars - a configuration never seen before.

Astronomers said the discovery, published in the Monthly Notices of the Royal Astronomical Society (MNRAS), marks a significant advancement in the understanding of brown dwarfs – elusive celestial objects too big to be planets but not massive enough to be stars.

As brown dwarfs occupy a unique middle ground between stars and planets, researchers say learning more about these enigmatic objects can offer critical insights into how stars evolve and planets form.

Hugh Jones, Professor of Astronomy at the University of Hertfordshire’s Centre for Astrophysics Research, said: “We are trying to understand brown dwarfs - objects that sit between stars and planets in terms of mass.

“They are faint, hard to detect, and we do not have any examples in our own Solar System.

“As far as we know, this is the first time a quadruple system has been found with two T-type brown dwarfs orbiting a pair of stars.

“Unlike our Sun, which is a singleton, most bigger stars are part of multiple-star systems.

“But smaller stars and brown dwarfs are usually single, and our findings are exciting because the chances of a low-mass brown dwarf having a companion are less than 5%.”

Brown dwarfs can be hard to detect because unlike red dwarfs - small, long-lived stars that make up about 80% of all the stars in the universe - they do not sustain hydrogen fusion - the nuclear process that makes stars shine.

These objects can also look similar at different ages, and it can be difficult to tell how old or massive a brown dwarf is based on its observable properties such as temperature or brightness - posing a fundamental challenge in brown dwarf research known as the "age-mass degeneracy problem".

However, if a brown dwarf is part of a multiple system with a star that is well understood, astronomers can estimate its age and mass based on the properties of the star.

But such “benchmark” systems are rare.

Prof Jones said: “When we find brown dwarfs both in orbit around each other as well as around stars it helps us a lot in comparing their properties to other objects.

“These so-called benchmarks are very valuable in the construction of models to describe these objects.”

He added: "Brown dwarfs with wide stellar companions whose ages can be determined independently are invaluable at breaking this degeneracy as age benchmarks.

"UPM J1040−3551 is particularly valuable because H-alpha emission (a specific red spectral line that arises from hydrogen atoms) from the brighter pair indicates the system is relatively young, between 300 million and two billion years old."

The quadruple system was identified by the Gaia astrometric satellite of the European Space Agency (Esa) and the Wide-field Infrared Survey Explorer (WISE) of Nasa.

The two pairs in the system are about 1,656 astronomical units (AU) apart (one AU is the distance between the Earth and the Sun).

The brighter pair, called UPM J1040−3551 Aab, includes two red dwarf stars that are equal in mass and look orange in visible light. They are about 100,000 times dimmer than the North Star and have a visual magnitude of 14.6.

The fainter pair, UPM J1040−3551 Bab, consists of two brown dwarfs that are much cooler and barely emit visible light. In near-infrared light, they are around 1,000 times dimmer than the red dwarf pair.

Astronomers used the Southern Astrophysical Research Telescope at Cerro Tololo Inter-American Observatory in Chile to study the system.

The telescope’s Goodman spectrograph captured visible light from the red dwarfs, while TripleSpec instrument captured infrared light from the brown dwarfs.

Analysis from both instruments revealed the red dwarfs are M-type stars, with temperatures of around 3,000°C and masses about 17% that of the Sun.

The T-type brown dwarfs are much cooler - one is 550°C, and the other is 420°C. Although about the same size as Jupiter, they are much heavier, with estimated masses 10 to 30 times greater.

The research was led by Professor Zenghua Zhang, of Nanjing University, and also involved scientists from the Brazilian National Astrophysics Laboratory, the Southern Astrophysical Research (SOAR) Telescope at Cerro Tololo Inter-American Observatory in Chile - a Program of NSF NOIRLab, and the Center for Astrobiology in Spain.

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