Astronomers have identified a rare, tightly bound star system in which an eclipsing binary—two stars that pass in front of each other from our perspective—also eclipses a third star, while the fourth star orbits ahead.

The international team of astronomers who made the discovery say it is the smallest quadruple star system ever found, because the outermost star, which orbits the inner three, has the shortest period on record. the studypublished Tuesday in Nature, provides a closer look at the strange and chaotic world of hierarchical star systems.

Four is a crowd

Using NASA’s Transiting Exoplanet Survey Satellite (TESS), the team behind the discovery searched for a triple star system and found one behaving strangely. Initially, the object’s brightness faded for about 1.5 days, indicating that it consisted of at least two stars orbiting each other. Then, every 26 days the object fades again, confirming that there is a third star in the system.

Further observations show that a triple star system is not sufficient to explain the nature of the object, with changes during eclipses revealing that an additional fourth star must be present in the system.

TESS observed the star system, named TIC 120362137, between 2019 and 2024. Astronomers used the data to determine the orbital period of the fourth star, which turned out to be 1,045.5 days long. That is the shortest orbital period for an outer fourth star ever observed in a system like this.

The inner three stars are all packed within an area similar in size to Mercury’s orbit around the Sun, while the fourth star is further away in an area comparable to Jupiter’s orbit. The three innermost stars are larger and hotter than the Sun, while the outermost companion is more similar to our host star.

“Stars are generally formed in groups by the collapse of large molecular clouds with dust and gas, and they can form different structures such as clusters, loosely bound associations, or binaries, triples, quadruples, etc., depending mainly on their formation environment and how gravitational interactions with other objects affect this process,” Tibor Mitnyan, a researcher from the University of Hungary and others yet. Gizmodo. “However, the formation of compact hierarchical systems is an actively studied area of ​​stellar astrophysics with many questions and uncertainties.”

A star pair

Using unique dynamical parameters, the team behind the study was also able to model the future evolution of this quadruple star system. In about 300 million years, the inner stars will merge into a white dwarf (an extremely dense core remnant of massive stars).

“The larger white dwarf was formed after two mergers from the three inner stars, while the less massive white dwarf was formed from the original fourth, most distant star,” Mitnyan said. The two remaining white dwarf stars will continue to orbit each other, completing one orbit in about 44 days.

“It is also interesting to note that if such a double white dwarf system were found today, observers would probably have no idea that it could be from an exotic compact 3 + 1 quadruple system with an external period of about a thousand days,” added Mitnyan.