It deserves a “whoa”: Astronomers have found a six-figure (six-) galaxy where, if you look at it a few days, every star in it will at some point undergo an eclipse.
Whoa.
Multiple stars are just intrinsically cool: unlike our sun, which travels through space alone, are multiples where two or more stars orbit in a stable, gravity-bound system. Half of the stars in the galaxy are in various systems like this. Most are binaries (two stars orbiting each other) and some in trinaries (three stars). Less is still in higher order systems.
This is the first thing that makes TYC 7037-89-1 special: it’s a sextet, a six – star system. It’s a little over 1,900 light – years away, so a fair distance, but it’s bright enough to be detected by TESS, the Transiting Exoplanet Survey Satellite. TESS scans the sky and measures the brightness of stars to search for transit exoplanets, which make mini-eclipses on their host stars, and reveal their presence.
But it can also find many other interesting things. TYC 7037-89-1 looks like one star in TESS data, but one that changes its brightness – a variable star. The astronomers who have found it search in TESS data for stars that change the brightness in a certain way, indicating that they are multiple galaxies.
What they were looking for is obscure binaries: Stars that not only orbit each other, but also stars where we see their orbits almost at the edge, so that it looks like the stars are going in front of another. When this happens, the total light of the pair drops in a characteristic way. The astronomers set up automated software to search for such stars, and out of nearly half a million, they found 100 that were apparently three-star systems or more.
And this is what brings out the second coolest thing about TYC 7037-89-1: it’s not just six stars that all orbit, but it’s also arranged in binaries: one pair of galaxies another few stars, and a third pair orbits both!
The binary pairs are named A, B and C in order of brightness, and each star in them gets the number 1 or 2 (again in order of brightness). The two inner binaries are then A (composed of stars A1 and A2) and C (C1 and C2), which orbit further around the orbit by the binary B (B1 and B2). A and C are separated by about 600 million kilometers (about the distance of Jupiter from the Sun), and it takes about 4 years to circumvent each other – 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, and takes 2,000 years to complete one period.
And now it brings out the coolest thing about this system: All three pairs of stars are obscuring binaries! We see that all three of the binary paths are almost on the edge. A1 and A2 undergo eclipses (A1 eclipse A2, then half a lane later A2 eclipse A1) every 1.57 days, so they are very close to each other. C1 and C2 rotate each other every 1.31 days, and B1 and B2 take 8.2 days.
Since each star in a given pair obscures the other, we can learn important things like how big the stars are, how hot they are, and more by measuring how long the eclipse takes, as well as other parameters (including taking spectra) . And it yields another surprise: All three binaries are very much the same. This is triplets!
In each, the larger 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, the smaller stars are about the same as each other: about 0.6 times the sun’s mass and 0.6 times its diameter. They vary slightly, but the point is that they are fairly close, which is peculiar.
This kind of system is just ridiculously unlikely. Models of how stars form show that sexes are much more made up of two trinitarian systems revolving around each other, not of three binaries. So it’s rare enough, but to show all three binaries seems impossible.
… “like.” In fact, it is likely that they are formed from a swirling disk material, and each star falls out of it. Therefore, it is likely that the three levels of the binaries are the same. Therefore, when we see one edge, we all see at the edge, or almost so. This does not make it as unlikely as you would think all three obscure.
I also note the orbits of the binaries around each other is not in progress. We see the orbit of A and C around each other from an angle of about 40 °, just as we see the individual stars in the binaries at the edge. However, the slopes of the orbit of B around them are not well limited by the observations.
Hopefully long-term study of this system will yield more information on how it formed. We do not know much about multiple systems like this, so it will be very interesting to understand under what circumstances it forms.
I know, it causes headaches. So many orbits, angles, stars … Sometimes nature is complex and hard to keep up with. 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 like TYC 7037-89-1 are known; for example CzeV1640 is a quadruple system with two pairs of obscure binaries. Nature is complex, but sometimes stingy, and uses the same idea over and over again.
But oh well, I would like a ship Undertaking now immediately! To get a closer look at myself, see these six stars – six! – dance around each other …
Indeed strange new worlds.