This deserves a “whoa”: astronomers have found a sextuple star system (of six) where, if you look at it for a few days, all the stars in it will experience an eclipse at some point.
Wow.
Several stars are intrinsically cool: unlike our Sun, navigating alone through space, the multiple are where two or more stars orbit each other in a stable, gravitationally bound system. Half of the galaxy’s stars are in multiple systems as well. Most are binary (two stars orbiting each other) and some are trinary (three stars). There is even less in higher order systems.
This is the first thing that makes the TYC 7037-89-1 special: it is a sextuplet, a six-star system. It is just over 1,900 light-years away, therefore, at a fair distance, but is bright enough to be detected by TESS, the satellite in transition on the exoplanet in transition. TESS scans the sky by measuring the brightness of the stars to look for exoplanets in transit, which make mini eclipses of the host stars, revealing their presence.
But you can also find many other interesting things. TYC 7037-89-1 looks like a star in the TESS data, but that changes its brightness: a variable star. Astronomers who have found it look in the TESS data for stars that change brightness in a certain way, indicating that they are multiple star systems.
What they were looking for are eclipsing binaries: Stars that not only orbit each other, but also those where we see their orbits almost edges, so that the stars seem to pass in front of another. When this happens, the total light of the torque falls a bit in a characteristic way. Astronomers set up automated software to search for these stars, and of nearly half a million, they found 100 that looked like systems with three stars or more.
And this is what makes the second interesting aspect of TYC 7037-89-1 appear: they are not just six stars orbiting all directions, but are arranged in binaries: a pair of star orbits another a pair of stars and a third pair orbit them both.
The binary pairs are called A, B and C in order of brightness, and each star is given the number 1 or 2 (again in order of brightness). The two inner binaries are A (formed by stars A1 and A2) and C (C1 and C2), orbited further by binary B (B1 and B2). A and C are separated by about 600 million kilometers (approximately the distance from Jupiter to the Sun), taking about 4 years to orbit; this was determined using archival data from other telescopes, including WASP and ASAS-SN. B orbits them both at a distance of about 38 billion km, taking 2,000 years to complete a period.
And this makes the most interesting of this system: The three pairs of stars are eclipsing binaries. We see the three binary orbits almost boundary. A1 and A2 experience mutual eclipses (A1 eclipses A2, then half an orbit later A2 eclipses A1) every 1.57 days, so they are very close. C1 and C2 orbit each other every 1.31 days and B1 and B2 take 8.2 days.
Because each star in a given pair eclipses the other, by measuring the time it takes the eclipse, as well as other parameters (including spectrum capture), we can learn important things like the degree of the stars, the heat that have and much more. And that gives way another surprise: the three binaries are very similar. They are twins!
In each of them, the largest star is about 1.5 times the diameter of the Sun, slightly warmer, and about 1.25 times the mass of the Sun. Also in each of them, the smaller stars are also about the same as others: about 0.6 times the mass of the Sun and 0.6 times its diameter. It varies a bit, but the point is that they are pretty close, which is quirky.
This type of system is ridiculously unlikely. Models of how stars form show that sextuples are most often formed by two trinary systems orbiting each other, not three binaries. So it’s weird enough, but it seems impossible to see all three binaries on time.
… “looks like”. In fact, they were likely to form from a swirling disk of material, with each star sinking. Because of this, it is likely that the three orbital planes of the binaries are the same. So if we look at an edge, we will see that they are all edge, or so. This makes it not as unlikely as one might think the three are eclipsing.
I will also write down the orbits of the binaries one around the other they are not limit. We see the orbits of A and C around each other from an angle of about 40 °, even when we see the individual stars in the binaries. However, the inclination of the B orbit around it is not well limited by observations.
We hope that the long-term study of this system will provide more information on how they were formed. We don’t really know much about various systems like this, so understanding under what conditions they are formed would be quite interesting.
I know, this causes a headache. So many orbits, angles, stars … Sometimes nature is complex and difficult to maintain. If it helps, I describe a similar fictional system that played a key role in the first season of Star Trek: Picard. And more systems are known as the TYC 7037-89-1; for example, CzeV1640 is a quadruple system with two pairs of eclipsing binaries. Nature is complex, but sometimes frugal, reusing the same idea over and over again.
But hey, I’d like a boat like this Company Right Now! To be able to see something so close, look at these six stars … sis! – dance next to each other …
Strange new worlds.