Four Stars In A Tiny Orbit

In the immensity of the Universe, stars are far from always evolving alone, like our Sun, which is in reality a statistical exception. A very significant proportion of them (if not the majority) belong to multiple systems, most often binary, sometimes triplewhose architectures are now well documented by observational astrophysics. Some of the most familiar stars illustrate this diversity, starting with Sirius, the famous binary system, or Alpha Centauri, our closest stellar neighbor, which forms a triple system.

But certain configurations remain exceptionally rare, particularly when several stars find themselves confined in extremely small orbital volumes. It is precisely this type of structure that an international team of astronomers has just described in a study published on March 3, 2026 in the journal Nature Communications : a remarkably compact quadruple star system.

Named TIC 120362137, this object was identified thanks to observations from the TESS satellite (Transiting Exoplanet Survey Satellite) from NASA. Photometric and spectroscopic analyzes show that three of the system’s stars form an extremely tight subset: they evolve in a region of space whose size is smaller than that of Mercury’s orbit around the Sun. Around this trio orbits a fourth star, more distant, in a significantly wider orbit. Astrophysicists refer to this type of hierarchical architecture as system ” 3+1 », a category still very little represented in stellar catalogs.

An incredibly tight gravitational ballet

Normally, TESS’s mission is to identify exoplanets thanks to variations in the brightness of the stars they orbit, and it is thanks to the sensitivity of its instruments that TIC 120362137 was spotted. By examining the data accumulated by the satellite, researchers indeed came across a star system of which several components eclipse each other, a much rarer phenomenon.

At the center of it all is what astrophysicists call a eclipsing binary : two stars whose orbit is aligned in such a way that they regularly pass in front of each other when seen from Earth. In the case of TIC 120362137, these two stars complete their revolution in just 3.28 days. Analysis of the variations in luminosity recorded by TESS, however, quickly showed that this duo was not evolving alone: a third star orbits around it in an orbit of approximately 51 days.

It was by analyzing the orbital movements inside TIC 120362137, in particular by measuring radial velocities (the speed of stars moving towards us or away) that the team highlighted the fourth star. Located at a much greater distance than the first three, this last star carries out a complete revolution around the whole in just under three years.

TIC 120362137 is therefore a system with quadruple stars: three of them, more massive and hotter than the Sun, occupy an extremely compact region of space, while a fourth star, with characteristics close to ours, orbits around this trio without ever crossing their trajectories. In fact, it is therefore the quadruple system of type “ 3+1 » the most compact ever identified which, on an astronomical scale, would fit almost entirely inside our Solar System.

TIC 120362137: a textbook case for astrophysics

In addition to its extremely rare compactness, the almost coplanar organization of the orbit of the four stars (they all rotate more or less ” flat ») probably indicates that they came from the same primordial disk of gas and dust. During the gravitational collapse of the cloud, this disk would have fragmented, giving birth to several stellar embryos which remained linked under this configuration.

In an orbital ensemble as tight as that of TIC 120362137, gravity acts intensely on the trajectories of the stars and their movements modify slightly over time: the orbital periods drift and the eclipses shift. These dynamic effects allow to estimate with great precision the physical properties of different stars which compose it.

As gravitational interactions are rapid and strongly constraining, these systems “ often make it possible to determine most stellar and orbital parameters », Specifies the team behind the study. Orbital shapes and periods, luminosity, surface temperature of stars, chemical composition: in a quadruple system, all these parameters are closely intertwined.

According to the team’s calculations, TIC 120362137, as currently observed, is certainly only at a frozen stage of its evolution. On time scales of several million years, the internal evolution of its stars and the exchanges of orbital energy would cause a rapprochement of the two most internal stars of the system. They could then merge, leaving behind white dwarfs, the final fate of the vast majority of stars in the Milky Way. Finally, the final reason which explains its immense scientific value : know if our models of star formation, generally developed from triple or binary systems, remain relevant when looking at systems such as TIC 120362137.