Why in news?

A team of international scientists has identified an extremely rare quadruple star system in the Milky Way, named UPM J1040−3551 AabBab. The system features a pair of cold brown dwarfs orbiting two young red dwarf stars — a configuration never observed before.

The study was published in the Monthly Notices of the Royal Astronomical Society (September issue).

Scientists say this discovery is significant as it provides fresh insights into brown dwarfs, celestial objects that are notoriously hard to detect and study, helping improve understanding of their properties and role in stellar evolution.

What’s in Today’s Article?

• Young Red Dwarf Stars
• Brown Dwarfs: The “Failed Stars”
• Why Brown Dwarfs Are Hard to Detect
• Importance of Studying Brown Dwarfs

Young Red Dwarf Stars

• Young red dwarf stars are small, relatively cool stars in the early stages of their long lifetimes. They are the most common type of stars in the Milky Way.
• High radiation: They are characterized by strong magnetic activity, leading to intense ultraviolet (UV) radiation and violent superflares, which can pose significant challenges to planetary atmospheres and life.
• Size & Temperature: They are smaller and cooler than our Sun, with surface temperatures ranging from about 2,500°C to 4,000°C.
• Longevity: Red dwarfs burn hydrogen fuel very slowly, allowing them to live for tens to hundreds of billions of years, far longer than stars like the Sun.
• Youth factor: When they are young, red dwarfs are more active, often emitting intense stellar flares and strong radiation.
• Importance in astronomy: Studying young red dwarfs helps scientists understand stellar evolution, the habitability of surrounding exoplanets, and how such stars influence planetary atmospheres.
• Proximity to Earth: The nearest star to our Sun, Proxima Centauri, is a red dwarf, highlighting the abundance and significance of these stars in our galactic neighbourhood.

Brown Dwarfs: The “Failed Stars”

• Brown dwarfs are unique celestial objects that form like stars from collapsing gas and dust but lack the mass to sustain hydrogen fusion, which powers normal stars.
• This limitation makes them faint and cooler, earning them the nickname “failed stars.”
• Despite this, they share characteristics with gas giants such as Jupiter and Saturn, having similar atmospheres filled with molecules like water vapor.
• Brown dwarfs can be massive—reaching up to 70 times the mass of Jupiter—yet remain distinct from true stars, occupying the gap between planets and stars in the cosmic family.

Why Brown Dwarfs Are Hard to Detect?

• Brown dwarfs are extremely cold and faint, making them difficult to observe directly.
• To study them, astronomers often track brown dwarfs that orbit brighter companion stars, since both objects are usually born together from the same material.
• By analysing the brighter stars, scientists can estimate the age, temperature, and composition of the dimmer brown dwarfs.
• The recent discovery of the quadruple star system UPM J1040−3551 AabBab is remarkable because it contains two T-type brown dwarfs, each about the size of Jupiter, orbiting two young red dwarf stars.
• Such a configuration is exceptionally rare — the probability of a low-mass brown dwarf having a companion is less than 5%, making this finding a valuable opportunity to deepen our understanding of these elusive “failed stars.”

Importance of Studying Brown Dwarfs

• Brown dwarfs help astronomers understand the processes behind star and planet formation, since they occupy the middle ground between the two.
• Mapping their abundance and distribution also provides crucial insights into how mass is spread across the universe.
• This is particularly significant because much of the universe’s mass remains unseen, existing as dark matter, and studying brown dwarfs offers valuable clues to this cosmic mystery.