A new star system has been discovered that contains 3 pairs of binary stars. But what makes it extra special is that all 3 of them are eclipsing binaries! Named TYC 7037-89-1, researchers found the system using data from NASA’s Transiting Exoplanet Survey Satellite (TESS). Brian P. Powell and Veselin Kostov headed up the international team, whose paper uses both archival data and new follow up observations.
What are Eclipsing Binaries?
We can answer this question by splitting it up. Firstly, a binary star system is one in which 2 stars orbit a common centre of gravity. This makes up as much as 50% of all star systems, maybe even 65%! An eclipse occurs when one body moves in front of the other, blocking out some (or all!) of its light. Of course, this entirely depends on your field of view. When we refer to eclipsing binaries we mean a star system with 2 stars that eclipse each other from our point of view on the Earth. There is no practical difference to an ordinary binary system, just the angle at which we see them!
But how do we know if a system has more than one star or not? Often, the distance between 2 stars in the same system is minute compared to the vast distance the light travels to meet us. This means that it can be difficult or impossible to resolve the ‘star’ into the 2 points of light it truly is. So scientists have to look closely at the amount of light we receive from that point.
Similar to the transit method used in exoplanet discovery, the brightness, or light curve, of an eclipsing binary varies as the stars move in front of each other. This manifests as dips in brightness as the light from one star is blocked by the other; the light curve rises again as they move apart. If the stars are of a similar size and brightness, the dips will have similar depths. But if they are different, we are able to see 2 different dips repeat in a periodic sequence as the stars complete their orbits.
When Binary Systems Meet
TYC 7037-89-1 is an extra special system: It has not one, but 3 eclipsing binary systems all orbiting each other! There are 2 systems, labelled A and C that orbit each other every 4 years, plus a third system, B, that orbits the centre of gravity between A and C. That particular orbit is extremely long; it takes B 2,000 years to complete one!
The most exciting thing about this system is that it is the first of its kind to be discovered. It is located about 1,900 light years from Earth. Each of the primary stars are a little bigger than our Sun but about the same temperature. The secondary stars are about half the size of our Sun.
Although TESS was originally designed to search for exoplanets using the transit method, the same principles can be used to discover multi-star systems like this one. Over 100 candidates for triple and quadruple systems have been found by the Goddard Space Flight Center in collaboration with the MIT Kavli Institute.
The discovery of TYC 7037-89-1 just goes to show how much variety there is in the universe. What kinds of star systems will be found next?