Astronomers in Brazil have just published in the Astronomical Journal evidence of a "giant Jupiter" planet in a distant and"exotic" star system in the Milky Way. As well as having 13 times the mass of Jupiter, the exoplanet is the first found that orbits an older or more evolved binary in which one of the two stars is dead.
What is a binary star?
Think our solar system is "normal?" Think again. The most common kind of star systems in our Milky Way galaxy are multiple stars systems, where two or more stars orbit each other, or rather, they orbit a common center of mass. Perhaps up to 85% of stars are in binary systems, including famous "stars" Sirius, Spica, Rigel, and Alpha Centauri. Binary stars are gravitationally bound to each other, so not to be confused with "double stars", which usually refer to stars that optically appear very close to each other line-of-sight in binoculars or a telescope, but may be in completely different star systems. There are plenty of triple and higher star systems, too. Polaris, the North Star, is a triple star system, while Kepler data has before been used to find "the impossible triple star" system KIC 2856960.
However, the KIC 10544976 star system is also unique.
What did the astronomers discover?
"We succeeded in obtaining pretty solid evidence of the existence of a giant exoplanet with a mass almost 13 times that of Jupiter in an evolved binary system," said lead author Leonardo Andrade de Almeida at the Federal University of Rio Grande do Norte (UFRN). "This is the first confirmation of an exoplanet in a system of this kind." Almeida and co-author Augusto Damineli studied close binary star system KIC 10544976, using data from ground-based telescopes between 2005 and 2017, and from the Kepler Space Telescope between 2009 and 2013. The Kepler Space Telescope, which completed its mission in 2018, has been responsible for the majority of the 4,000+ exoplanet discoveries so far.
What is KIC 10544976?
KIC 10544976 contains a white dwarf star (a dead low-mass star with high surface temperature) and a red dwarf star (a live magnetically active star with a small mass compared to our Sun) that orbit each other in rapidly every 0.35 days. "The system is unique," said Almeida. "No similar system has enough data to let us calculate orbital period variation and magnetic cycle activity for the live star."
KIC 10544976 is in the constellation of Cygnus "the Swan" in the northern celestial hemisphere, a region studied closely by the Kepler Space Telescope.
How was the "giant Jupiter" discovered?
The stars' orbits vary slightly, which the astronomers noticed from variations in the time taken for each of the two stars to eclipse each other. "Variations in the orbital period of a binary are due to gravitational attraction among the three objects, which orbit around a common center of mass," said Almeida. The key to the study was to research the magnetic activity cycle of the binary's "live" red dwarf star by monitoring the rate and energy of solar flares and the variability in its luminosity caused by sun-spots. "Variations in our Sun's magnetic activity eventually cause a change in its magnetic field," said Almeida."The same is true of all isolated stars. In binaries, these variations also cause a change in the orbital period due to what we call the Applegate mechanism."
The researchers measured magnetic cycles and found their results were what would be expected for single low-mass stars, and found only one long-term variation. "This completely refutes the hypothesis that orbital period variation is due to magnetic activity," said Almeida. "The most plausible explanation is the presence of a giant planet orbiting the binary, with a mass approximately 13 times that of Jupiter."
Why we need to get a closer look at "giant Jupiter
How did "giant Jupiter" form and evolve? Is it a "first-generation" planet that developed at the same time as the two stars billions of years ago? Or did it form out of the gas ejected during the death of the white dwarf, making it a second-generation planet? Is there life on "giant Jupiter?" These are questions that can only be answered by ground-based telescopes with primary mirrors exceeding 20 meters, which is why the São Paulo Research Foundation (FAPESP) is investing US$40 million in the Giant Magellan Telescope (GMT), which is currently being constructed in Chile's Atacama Desert and expected to see first light in 2024.
"We're probing 20 systems in which external bodies could show gravitational effects, such as KIC 10544976, and most are only observable from the southern hemisphere," said Almeida. "The GMT will enable us to detect these objects directly and obtain important answers on the formation and evolution of these exotic environments, as well as the possibility of life there."
The future of exoplanet-hunting
With the launch of the Kepler Space Telescope in 2011, exoplanet-hunting became arguably the hottest genre in astronomy and planetary science. That mission ended in October 2018, but the launch in April 2018 of TESS (Transiting Exoplanet Survey Satellite) is expected to bring many more exoplanet discoveries that can be confirmed by a new generation of giant ground-based telescopes.
Wishing you clear skies and wide eyes
Follow me on Twitter @jamieacarter, @TheNextEclipse or read my other Forbes articles via my profile page.
I'm a science and travel journalist interested in nature, exploring the night sky, solar and lunar eclipses, and astro-travel.