Using NASA's exoplanet-hunting spacecraft, the Transiting Exoplanet Survey Satellite (TESS), scientists have discovered a record-breaking triple star system so closely linked that it could fit comfortably between the Sun and the nearest planet, Mercury.
The system, named TIC 290061484, contains twin stars that race around each other once every 1.8 Earth days, as well as a third star that orbits the pair once every 25 Earth days. The super-close orbit of this triple star system, located just under 5,000 light-years away in the constellation Cygnus the Swan, makes it a record breaker.
The previous record holder for the tightest orbit of the three-star system is Lamba Tauri, which set the record in 1956 when its third star took 33 days to orbit its inner twin stars.
Related: A giant exoplanet the size of two Jupiters has a hidden companion that is disrupting its orbitThe discovery team consisted of citizen scientists who met as part of the now-closed Planet Hunters project, which ran from 2010 to 2013. The amateurs, along with professional astronomers, formed the Visual Survey Group collaboration, which has been active for a decade.
"The system's compact, edge-on configuration allows us to measure the orbits, masses, sizes and temperatures of its stars," team member Veselin Kostov of NASA's Goddard Space Flight Center and part of the SETI Institute said in a statement. "We can study how the system is formed and predict how it might evolve."
Three's company
The team believes that the star system TIC 290061484 is very stable because the stars orbit each other in almost the same plane. If the stars' orbits were tilted in different directions, their gravitational influences would disrupt their orbits, making the system unstable.
However, this stability will not last forever - perhaps a few million years. While that's a long time for us, it's the blink of an eye in our 13.8 billion- year old cosmos. And as Visual Survey Group team member Saul Rappaport, professor of physics at the Massachusetts Institute of Technology (MIT), reminds us, referring to the fate of the TIC 290061484 stars: "No one lives here."
As the twin stars at the core of this triple star system age, they will expand outward and eventually merge. This will cause a massive supernova explosion in about 20 to 40 million years. Fortunately, this is unlikely to affect any life on the planets around the three stars, as there don't appear to be any planets close enough to the stars to support life (as we know it, at least).
"We think the stars formed together from the same growth process, which prevented planets from forming very close around one of the stars," says Rappaport.
However, it is possible that a very distant planet exists in the TIC 290061484 system, orbiting the three stars as if they were one.
The promise of the Roman telescope
The team spotted the record-breaking triple star system thanks to the flashing starlight caused by the stars crossing in front of each other, as seen from our position on Earth.
The team turned to machine learning to analyze massive amounts of data from TESS and discover a pattern that indicates these eclipses. They then enlisted the help of citizen scientists to further filter this data to detect interesting signals.
"We are mainly looking for signatures of compact multi-star systems, unusual pulsating stars in binary systems and strange objects," Rappaport said. "It's exciting to identify a system like this because they are rarely found, but they may be more common than current numbers suggest."
The team believes there are likely many more such systems scattered across the Milky Way, waiting to be discovered. Some may even exhibit shorter orbits than the stars of the TIC 290061484 system. Current technology may be insufficient to discover these closely linked triple stars, but help is on the way.
The Nancy Grace Roman Space Telescope, or simply 'Roman', will launch no earlier than May 2027 and will provide much more detailed images of space than those collected by TESS.
NASA's exoplanet hunter takes a wide view of the cosmos, while Roman takes a "zoomed in" look. To put this into perspective, an area of space covered by a single pixel in an image from TESS will contain as many as 36,000 pixels in an image from Roman. This allows Roman to see deep into the heart of the Milky Way, where the stars are densely packed.
"We don't know much about many of the stars at the center of the Milky Way, except the brightest ones," said team member and Goddard data scientist Brian Powell. "Roman's high resolution will help us measure the light from stars that usually blur together, giving us the best look yet at the nature of galaxies in our Milky Way."
One of Roman's main missions will be monitoring the light from hundreds of millions of stars, which should help astronomers discover the flash effect that the TIC 290061484 system revealed.
"We're curious why we haven't yet found galaxies like this with an even shorter orbital period," Powell explains. "Roman should help us find them and get us closer to figuring out their limits."
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Roman may even allow scientists to discover tightly packed galaxies with more than three stars, perhaps as many as six, buzzing around each other like bees in a beehive.
"Before scientists discovered triple-eclipsing triple star systems, we didn't expect them to exist there," team member Tamás Borkovits of the Baja Observatory in Hungary said in the statement. "But once we found them, we thought, why not?
"Roman may also reveal never-before-seen categories of systems and objects that will surprise astronomers."
The team's research was published Tuesday (Oct. 2) in the Astrophysical Journal.