Astronomers have identified a remarkably dense quadruple star system, TIC 120362137, packed so tightly that its inner stars could fit within the orbit of Mercury around our Sun. The discovery, made using NASA’s TESS spacecraft, marks the closest-known example of a “3+1” configuration – three stars orbiting each other closely, with a fourth orbiting at a greater distance.
Unveiling the System’s Complexity
The system’s structure is hierarchical: a tight inner trio of stars surrounded by a more distant fourth star. The outermost star orbits at roughly the same distance from the triplet as Jupiter from our Sun, while the inner trio is compressed into an area smaller than Mercury’s orbit. This extreme compactness makes it unique among known quadruple star systems.
Why This Discovery Matters
The rarity of such configurations makes TIC 120362137 a valuable research subject. Studying it will help scientists refine their understanding of how stars form in crowded environments and how stable multiple-star systems can remain over billions of years. The extreme proximity of these stars challenges existing models and offers a natural laboratory for testing gravitational interactions.
The Discovery Process
Initial observations from TESS showed regular dips in brightness, indicating eclipsing binary stars (two stars passing in front of each other). Further analysis revealed additional, periodic dimming events, suggesting the presence of a third star. It wasn’t until detailed spectroscopic data from the Tillinghast telescope confirmed the existence of a fourth star.
“By a simple inspection of the early TESS data, we realized that TIC 120362137 is a compact, tight, triply eclipsing triple star system,” team leader Tamás Borkovits stated.
Long-Term Fate: A Binary White Dwarf System
Computer simulations reveal the system’s ultimate fate. Over hundreds of millions of years, the inner three stars will merge through successive binary interactions, eventually forming a single, massive star. This star will then collapse into a white dwarf. The distant fourth star will follow a similar path, creating a final binary system of two white dwarfs orbiting each other in just 44 days.
“First, the most massive star…will reach the red giant state. In that state, it will merge with its mate…Then, in around 276 million years…this new, merged star…will merge with the third stellar component,” Borkovits explained.
This discovery highlights the chaotic yet predictable evolution of multiple-star systems, where gravitational interactions drive dramatic changes over cosmic timescales. The final result will be a compact binary of stellar remnants, a testament to the dynamic forces at play in the universe.
