For us humans, a single Sun feels completely normal, but our solar system is actually a strange aspect. Most stars in the Milky Way galaxy have at least one companion star. Now, in a system 1,800 light-years away, astronomers have finally confirmed a gas giant planet orbiting a star in a three-star system.
This system, called KOI-5, is located in the constellation of Cygnus, and the exoplanet there has been confirmed more than a decade after it was first detected by the space hunting telescope on the planet Kepler.
In fact, the planet (now known as KOI-5Ab) was the second candidate to detect exoplanets conducted by Kepler when it began operations in 2009. But it fell backwards.
“The KOI-5Ab was abandoned because it was complicated and we had thousands of candidates,” said astronomer David Ciardi of NASA’s Exoplanet Science Institute.
“There were easier selections than KOI-5Ab and every day we learned something new from Kepler, so KOI-5 was mostly forgotten.”
Exoplanet hunters tend to avoid the complexity of multi-star systems; of the more than 4,300 confirmed exoplanets to date, less than 10% belong to multi-star systems, although these systems dominate the galaxy. As a result, very little is known about the properties of exoplanets in multi-star systems, compared to those orbiting a lone star.
After Kepler’s detection, Ciardi and other astronomers had used ground-based telescopes such as the Palomar Observatory, the WM Keck Observatory, and the Gemini North Telescope to study the system. In 2014 they had identified two companion stars, KOI-5B and KOI-5C.
This made it extremely difficult to find out whether the falling starlight observed by Kepler was caused by an exoplanet or something else. The project appeared in the basket too hard.
In 2018, Kepler’s successor, TESS, took over the job. And when TESS looked at Cygnus, it also pinged a candidate exoplanet orbiting KOI-5A.
“I thought,‘ I remember that goal, ’” Ciardi said. “But we still couldn’t definitively determine if the planet was real or if the data information came from another star in the system: it could have been a fourth star.”
He and his team set to work, reanalyzing all of the above data. In an excellent testament to the abilities of our planetary hunting telescopes, the researchers found that yes, in fact, there is an exoplanet orbiting KOI-5A, at a biased angle with at least one of the stars. of the triple system.
“We don’t know many planets that exist in three-star systems, and this one is very special because its orbit is skewed,” Ciardi said.
What the scientists were able to ascertain is that the planet, KOI-5Ab, is probably a gas giant about half the mass of Saturn and 7 times the size of Earth, in a very close five-day orbit around KOI -5A. KOI-5A and KOI-5B, both around the same mass as the Sun, form a relatively close binary, with an orbital period of about 30 years.
The third star, KOI-5C, orbits the binary at a much greater distance, with a period of about 400 years, slightly larger than Pluto’s 248-year orbit.
(Caltech / R. Hurt (IPAC))
So if you were able to stop at KOI-5Ab, KOI-5A would dominate the sky. The KOI-5B would closely resemble Saturn’s Sun (that of Saturn in a 29-year solar orbit). And KOI-5C would look like a very bright star.
And the orbit of KOI-5Ab is misaligned with KOI-5B, which is interesting. If all objects had formed from the same swirling disk of material, they would have to be aligned more or less in the same plane as the planets in the solar system around the Sun’s equator. Researchers think that KOI-5B may have gravitationally disrupted the exoplanet’s orbit, ejecting it from alignment as the planet formed.
We have seen other evidence to suggest that this may happen. Last year a three-star system with an almost annoying protoplanetary disk was revealed. Any planet that forms on it will probably end up in rather strange orbits.
Therefore, although we have not confirmed many exoplanets in triple-star systems, finding more will help astronomers model these processes and find out the wild dynamics involved.
“We still have a lot of questions about how and when planets can form in multi-star systems and how their properties compare to planets in single-star systems,” Ciardi said.
“By studying this system in more detail, perhaps we can get an idea of how the Universe makes planets.”
The discovery was announced at the 237th meeting of the American Astronomical Society.