Astrophysicists Identify Record-Breaking Compact '3+1' Quadruple Star System

The astrophysical community has officially identified TIC 120362137 as the most compact "3+1" multiple star system ever recorded. This landmark discovery, detailed in the March 2026 issue of Nature Communications, offers a rare window into the extreme gravitational dynamics found within hierarchical stellar structures. Led by Hungarian astronomer Tamás Borkovits from the University of Szeged, the research team included experts from China, the Czech Republic, and Slovakia. Their findings provide critical insights into the long-term stability and complex orbital mechanics of densely packed stellar ensembles.

The architectural layout of TIC 120362137 is remarkably tight, consisting of a trio of closely bound stars forming a central core, with a fourth, more distant star orbiting the group. Scientists have calculated that the three inner components are so proximity-bound that they would fit entirely within the orbit of Mercury around our Sun. Meanwhile, the fourth outer star maintains an orbit comparable to the distance between Jupiter and the Sun. Notably, the three inner stars are both more massive and significantly hotter than our Sun, whereas the outer component shares a closer resemblance to our own star. Located approximately 1,900 light-years away, this configuration holds a new record: the outermost star completes its orbit in just 1,046 days, a duration significantly shorter than any other known "3+1" system.

At the heart of this system lies an eclipsing binary pair with a rapid orbital period of just 3.3 Earth days, which in turn orbits a third star every 51.3 days. Detecting such intricate systems is notoriously difficult, as identifying a fourth component through eclipse timing variations requires extensive observation windows. To overcome this, researchers synthesized data from NASA’s Transiting Exoplanet Survey Satellite (TESS) collected between 2019 and 2024 with ground-based observations. Specifically, they utilized the Tillinghast Reflector Echelle Spectrograph (TRES), mounted on the 1.5-meter Tillinghast telescope at Mount Hopkins in Arizona. For the first time in such a system, the spectral signatures of all four stars were captured directly, allowing for highly precise measurements of their masses and orbital trajectories.

Advanced numerical simulations suggest that the extreme proximity of these stars will eventually lead to mass transfer and inevitable mergers. Projections indicate that in roughly 9.39 billion years, this quartet will evolve into a stable pair of white dwarfs. The process begins with the inner primary star merging with its partner to form a new body, designated A'. Approximately 276 million years later, A' is expected to merge with the third star, B, creating a massive star AB that will ultimately collapse into a white dwarf. The fourth, outer star will undergo its own evolutionary journey to become a second white dwarf, resulting in a binary white dwarf system with an orbital period of about 44 days. This discovery provides empirical support for models predicting that such dense configurations can remain stable for billions of years before reaching their final evolutionary state.

The identification of TIC 120362137 was bolstered by the contributions of citizen scientists who assisted in analyzing TESS data, highlighting the collaborative nature of modern astronomy. Methodologically, the ability to directly detect the spectra of all four stellar components represents a significant leap forward, moving beyond traditional light-curve analysis. By studying such precisely balanced hierarchical systems, astronomers gain invaluable data to test and refine theories of stellar evolution under conditions of extreme density. This case study serves as a benchmark for understanding how complex star systems form and persist throughout the cosmos.