Our Solar System is a normal, regular kind of star system where a bunch of planets orbit one star, right? Not so—it’s thought that most stars are in binary systems, where two Suns orbit each other.
Triple star systems are common, too, but a new and bizarre sextuple system just found by astronomers at NASA’s Goddard Space Flight Center ups the stakes.
Stars can get in pretty peculiar configurations, which are often difficult to spot and even more difficult to model. But system TIC 168789840 truly is almost too extraordinary to be described. It is the first six-star system discovered where each pair of stars are eclipsing binaries. The system consists of three gravitationally-bound binary stars in a hierarchical structure of an inner quadruple system with an outer binary subsystem.
NASA’s TESS has discovered a distant star system that scientist Brian Powell says exist against all odds. Powell is a data scientist at the NASA High Energy Astrophysics Science Archive Research Center. The star system in question is called TIC 168789840 and it resides approximately 1900 light years from Earth in the constellation of Eridanus.
TIC 168789840 (also known as TYC 7037-89-1), becomes the first known “sextuply-eclipsing sextuple star system.”
The star system has three binary pairs of stars revolving around three different centers of mass. The trio of binary stars are gravitationally bound to one another, circling the galactic center as a single star system. Many of the star systems that TESS has discovered are triple and quadruple star systems. However, when TIC 168789840 was discovered it baffled scientists because it was mysteriously brightening and dimming.
What is an eclipsing binary star?
It’s all about our line of sight. An eclipsing binary star system is typically a star system of two stars that orbit each other, or rather, they orbit around their center of mass. The only difference between an eclipsing binary system and any other binary star system is our line of sight—if TESS, or any telescope, can see the two stars eclipse each other, they’re called “eclipsing binaries.”
Why are eclipsing binary stars important?
While a planet moving across a star from our line of sight is the best way to find a planet, two stars eclipsing each other gives astronomers a lot more information about the actual star.
From observing the light-curves from eclipsing binaries astronomers can measure the sizes, masses and temperatures of the two stars, as well as their distance from each other and their distance from us.
Why is TYC 7037-89-1 an incredible find?
In the case of TYC 7037-89-1 the data might help astronomers untangle how the primary and secondary stars became so similar and also how the three systems became gravitationally bound.
It could give astronomers new insight into the formation, dynamics, and evolution of multiple star systems.
Where is TYC 7037-89-1?
It’s about 1,900 light-years away in the constellation Eridanus, the river. If you want to visualize where it is in the night sky, go outside after dark and find Orion high in the southeastern sky, and very bright star Sirius below. Rigel in Orion and Sirius will form a vast triangle with TYC 7037-89-1 as the third unseen point.
“Prior to the discovery of TIC 168789840, there were 17 known sextuple star systems according to the June 2020 update of the Multiple Star Catalog,” stated Brian Powell. “Our analysis shows that the orbital periods of the three constituent eclipsing binaries are 1.57 days (binary A), 1.3 days (binary C) and 8.2 days (binary B), such that binaries A and C form an inner quadruple system with a period of about 4 years, and the latter forms the outer subsystem with a period of about 2,000 years,” the astronomers wrote.
They observed all six eclipses — three primary and three secondary — in the TIC 168789840 system using NASA’s Transiting Exoplanet Survey Satellite (TESS).
“Interestingly, of the known sextuple systems, TIC 168789840 is most similar to the famous Castor system, which also contains three close binaries,” they wrote.
The three binary stars in the system are ‘triplets,’ as each binary is similar to the others in terms of mass, radius, and temperature.
The primary stars in the binaries have masses between 1.23 and 1.3 times that of the Sun and radii between 1.46 and 1.69 solar radii, while the secondary stars have masses and radii of 0.56-0.66 solar masses and 0.52-0.62 solar radii.
“TIC 168789840 is a fascinating system that naturally merits additional observation and analysis,” the authors wrote.
“Though quite similar to the Castor system, the triplet nature of TIC 168789840 combined with the presence of three primary and three secondary eclipses enable further investigations into its stellar formation and evolution.”
“Remarkable objects like TIC 168789840 or Castor give us insights on the formation of multiple systems — a matter of active research and debate.”
The team’s paper will be published in one of the AAS journals.