Astronomers have identified the tightest known quadruple star system exhibiting a rare ”3+1” orbital arrangement, where a single star orbits a closely bound trio. Designated TIC 120362137, this system was discovered through observations by NASA’s TESS space telescope.
In this setup, three stars form an extremely close inner group, while a fourth star orbits at a much greater distance. For TIC 120362137, the trio’s orbits fit within a zone comparable in size to Mercury’s path around the Sun, with the outer star tracing an orbit just inside Jupiter’s average distance.
Systems like these, especially with components of similar mass, are generally thought to be gravitationally unstable-close interactions tend to disrupt their structure. That makes TIC 120362137’s stability a valuable case for testing stellar dynamics theories under extreme conditions.
One co-author explained this quadruple is unique not only in compactness but also in the ability to spectrally distinguish all four stars individually, enabling precise measurement of each star’s characteristics.
Observations of eclipses and spectral signatures have revealed detailed parameters: the innermost pair orbit each other every 3.28 days, with masses roughly 75% and 36% greater than the Sun’s. The third star orbits this pair every 51.3 days and is about 48% more massive than the Sun. The outermost star, similar in mass to the Sun, completes an orbit around the inner trio every 1,045.5 days.
Remarkably, despite these tight orbits, the system remains dynamically stable, as confirmed through orbital period ratios and comprehensive computer simulations projecting its evolution over billions of years.
Models predict that in about 300 million years, after the stars pass through their red giant phases and shed mass, the three inner stars will merge into a single white dwarf. Over roughly 9.4 billion years, the system will evolve into a white dwarf binary with an orbital period near 44 days.
This research suggests that some currently observed binary white dwarfs may have originated from such intricate quadruple systems, although tracing back such histories remains nearly impossible. The astronomers emphasize that, if found today, the white dwarf binaries might not hint at their exotic past involving a complex 3+1 stellar hierarchy.
The discovery pushes the boundaries of our understanding of how multiple star systems can form and remain stable, challenging assumptions about the fragility of close quadruple stellar arrangements.