Astronomers have identified a rare and extraordinary triple star system in our galaxy using NASA’s Transiting Exoplanet Survey Satellite (TESS). Designated TIC 295741342, the system features two sun-like stars in a close binary, orbited by a massive third star that produces a triply-eclipsing event, a phenomenon observed in only a handful of systems. The discovery was reported on arXiv on May 19, offering new insights into stellar evolution and the dynamics of multi-star systems.
A Rare Stellar Alignment Captured by TESS
The discovery of TIC 295741342 highlights TESS’s versatility beyond exoplanet detection. While designed to monitor 200,000 bright stars for transiting planets, the satellite also tracks intricate interactions in multi-star systems. In this case, TESS captured a highly unusual dip in the light curve of the system, revealing a triply-eclipsing event.
“The shape of the eclipse demonstrates the secondary of the eclipsing binary passing fully behind a larger star (first shoulder), followed by the primary together with the secondary (the head), followed by the primary emerging from behind the tertiary (second shoulder),” the researchers explained. This “head-and-shoulders” pattern allows astronomers to precisely measure the relative brightness and sizes of the stars, a feat rarely possible for triple systems. The clarity of the light curve demonstrates TESS’s exceptional sensitivity to complex stellar interactions.
System Parameters and Stellar Composition
The inner binary of TIC 295741342, labeled Aa and Ab, consists of main-sequence stars remarkably similar to our Sun, each with a temperature of about 6,400 K and orbiting each other every 4.75 days. The tertiary companion, TIC 295741342 B, is a giant star with 1.7 solar masses and a radius more than 10 times that of the Sun, orbiting the binary at roughly 1.7 AU every 1.13 years. Its effective temperature measures 4,839 K, giving it a cooler, more expanded profile than the inner pair.
The system’s metallicity is estimated at -0.337 dex, and its age is about 1.46 billion years, while its distance from Earth is approximately 3,080 light-years. The inner binary contributes minimally to the system’s total light, with the tertiary dominating 95% of observed brightness in TESS data. The near-perfect coplanarity of the system, with a mutual inclination of only 0.25–0.33 degrees, makes it an exceptional laboratory for studying orbital dynamics.
Insights Into Formation and Stellar Evolution
The configuration of TIC 295741342 provides critical clues about its formation. According to the study, the system likely formed through disk fragmentation, followed by inward orbital migration and gas dissipation. Such a formation scenario accounts for the near-perfect coplanarity and compact orbital arrangement.
“TIC 295741342 is one of only a handful of known triply-eclipsing triple star systems with a giant tertiary, and it has by far the lowest mutual inclination among them,” the researchers conclude. This finding emphasizes the rarity of the system and its importance for understanding how multi-star systems evolve over time. Observing such systems can refine models of stellar interactions, mass transfer, and gravitational influences that shape orbital dynamics.
Future Prospects for Observation and Study
With the triply-eclipsing event providing a rare glimpse into complex stellar behavior, astronomers plan to continue monitoring TIC 295741342. The system offers a natural laboratory for testing theories of orbital mechanics, tidal interactions, and long-term evolution of hierarchical triple systems. TESS’s ongoing survey will likely uncover more rare systems, expanding our understanding of how stars interact in compact, multi-body configurations.
The discovery underscores the continuing value of archival and ongoing data from TESS, while also highlighting the potential for citizen scientists and professional astronomers alike to detect and study rare stellar phenomena. The system’s publication on arXivensures rapid dissemination to the global scientific community.
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