Epoch J2000 Equinox J2000
|Right ascension||04h 14m 04.867s|
|Declination||−31° 55′ 22.36″|
|Apparent magnitude (V)||11.51|
|Proper motion (μ)|| RA: 12.082 mas/yr |
Dec.: 9.513 mas/yr
|Parallax (π)||1.6861 ± 0.4296 mas|
|Surface gravity (log g)||4.18 cgs|
|Rotational velocity (v sin i)||48.5 km/s|
|Surface gravity (log g)||4.73 cgs|
|Rotational velocity (v sin i)||17.5 km/s|
|Surface gravity (log g)||4.12 cgs|
|Rotational velocity (v sin i)||10.1 km/s|
|Surface gravity (log g)||4.67 cgs|
|Rotational velocity (v sin i)||3.8 km/s|
|Surface gravity (log g)||4.24 cgs|
|Rotational velocity (v sin i)||51.5 km/s|
|Surface gravity (log g)||4.72 cgs|
|Rotational velocity (v sin i)||20.9 km/s|
TIC 168789840 is a stellar system with six stars. Three pairs of binary stars circle a common barycenter. While other systems with three pairs of stars have been discovered, this was the first system where the stars can be observed eclipsing one another, as their planes of rotation point approximately towards the Earth.
The Transiting Exoplanet Survey Satellite identified that the star system consisted of six eclipsing stars. The discovery was announced in January 2021. It is approximately 1,900 light-years (584 pc) from Earth, in the constellation Eridanus, west of the river asterism's sharpest bend, Upsilon2 Eridani, often called Theemin. To be seen the group needs strong magnification from Earth as is much fainter than red clump giant star Theemin and is about nine times further away.
Two sets of the binaries co-orbit relatively closely, while the third pair of stars takes 2,000 years to orbit the entire system barycenter. The inner A pair and C pair orbit each other in 3.7 years. These are, as taken from the paired B stars, about 250 AU away (specifically the mean telescopic separation is 423 mas) and the three lettered pairs, as groups, have been resolved (the three gaps made out). From A pair to C pair is calculated to be 4 AU (∼7 mas) apart, which means this gap should be resolvable using speckle interferometry which has not yet been achieved.
The primary stars of all three close binaries are slightly hotter and brighter than the Sun, while the secondary stars are much cooler and dimmer. Because the two closely bound pairs are so close, only the third, more distant pair could have planets. The primaries are all beginning to evolve away from the main sequence, while the less massive and longer-lived secondaries are all still firmly on the main sequence and fusing hydrogen in their cores.
But only one of the pairs could have any planets. Two of the system’s binaries orbit extremely close to one another, forming their own quadruple subsystem. Any planets there would likely be ejected or engulfed by one of the four stars. The third binary is farther out, orbiting the other two once every 2,000 years or so, making it a possible exoplanetary haven.
The system, also called TIC 168789840, is the first known sextuple composed of three sets of eclipsing binaries, stellar pairs whose orbits tip into our line of sight so we observe the stars alternatively passing in front of each other.
The primary stars in all three binaries are all slightly bigger and more massive than the Sun and about as hot. The system, also called TIC 168789840, is located about 1,900 light-years away in the constellation Eridanus.
'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,' lead author Dr. Brian Powell of NASA’s Goddard Space Flight Center and colleagues wrote in their paper.