In the last three decades, almost 4,000 objects similar to planets have been discovered orbiting isolated stars outside the Solar System (exoplanets). As of 2011, it was possible to use the NASA Kepler Space Telescope to observe the first exoplanets in orbit around young binary systems of two living stars with hydrogen still in their nucleus.
Brazilian astronomers have now found the first evidence of the existence of an exoplanet that orbits an older or more evolved binary in which one of the two stars is dead.
The study resulted from a postdoctoral research project and a research internship abroad, both with FAPESP scholarships. Their findings have just been published in The Astronomical Journal, property of the American Astronomical Society (AAS).
Leonardo Andrade de Almeida, first author of the article, told Agência FAPESP: "We managed to obtain quite solid evidence of the existence of a giant exoplanet with a mass almost 13 times greater than that of Jupiter. [the largest planet in the Solar System] In an evolved binary system. This is the first confirmation of an exoplanet in a system of this type. "
Almeida is currently a postdoctoral fellow at the Federal University of Rio Grande do Norte (UFRN) and has conducted postdoctoral research at the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG-USP) of the University of São Paulo, where he was supervised by Professor August. Damineli, co-author of the study.
The clues followed by researchers to discover the exoplanet in the evolved binary called KIC 10544976, located in the constellation of Cygnus in the Northern Celestial Hemisphere, included variations in eclipse time (the time it takes for each of the two stars to eclipse to the other) and period.
"The variations in the orbital period of a binary are due to the gravitational attraction between the three objects, which orbit around a common center of mass," said Almeida.
However, the variations of the orbital period are not sufficient to demonstrate the existence of a planet in the case of binaries, because the magnetic activity of binary stars fluctuates periodically, just as the magnetic field of the Sun changes polarity every 11 years , with turbulence and the number and size of sunspots reach their peak and then decrease.
"Variations in the magnetic activity of the Sun eventually cause a change in its magnetic field, as do all isolated stars." In binaries, these variations also cause a change in the orbital period due to what we call the mechanism of Applegate, "explained Almeida.
To refute the hypothesis that the variations in the orbital period of KIC 10544976 were due only to magnetic activity, the researchers analyzed the effect of the variation of the eclipse timing and the magnetic activity cycle of the binary live star.
KIC 10544976 consists of a white dwarf, a dead star of low mass with a high surface temperature, and a red dwarf, a living star (magnetically active) with a small mass compared to our Sun and low light due to low energy production. The two stars were monitored by ground-based telescopes between 2005 and 2017 and by Kepler between 2009 and 2013, producing minute-by-minute data.
"The system is unique," said Almeida. "No similar system has enough data to allow us to calculate the variation of the orbital period and the activity of the magnetic cycle for the living star."
Using Kepler's data, they were able to estimate the magnetic cycle of the living star (red dwarf) based on the speed and energy of the eruptions (large eruptions of electromagnetic radiation) and the variability due to the dots (regions of colder temperature). of the surface and, therefore, darkness). caused by different concentrations of magnetic field flux).
The analysis of the data showed that the cycle of magnetic activity of the red dwarf lasted 600 days, which is consistent with the estimated magnetic cycles for isolated stars of low mass. The orbital period of the binary was estimated at 17 years.
"This completely refutes the hypothesis that the variation of the orbital period is due to magnetic activity. "The most plausible explanation is the presence of a giant planet that orbits the binary, with a mass approximately 13 times greater than that of Jupiter," said Almeida.
It is unknown how the planet that orbits the binary was formed. One hypothesis is that it developed at the same time as the two stars billions of years ago. If so, it is a first generation planet. Another hypothesis is that it was formed from the gas expelled during the death of the white dwarf, making it a second-generation planet.
The confirmation of its status as a first or second generation planet and its direct detection as it orbits the binary could be obtained using the new generation of terrestrial telescopes with primary mirrors that exceed 20 meters, including the Giant Magellan Telescope (GMT) installed in the Atacama desert in Chile. The GMT is expected to see the first light in 2024.
FAPESP will invest US $ 40 million in the GMT, or approximately 4% of the estimated total cost of the telescope. This investment will guarantee 4% of the operating time of the telescope for the studies carried out by researchers from the state of São Paulo (read more at: agencia.fapesp.br/28569).
"We are investigating 20 systems in which external bodies could show gravitational effects, such as KIC 10544976, and most can only be observed from the southern hemisphere.The GMT will allow us to detect these objects directly and obtain important answers about the formation and evolution of these exotic environments, as well as the possibility of life there, "said Almeida.
The article "Variation of the orbital period of KIC 10544976: Application mechanism versus effect of travel time of light" (DOI: 10.3847 / 1538-3881 / ab0963) by Leonardo A. Almeida, Leandro de Almeida, Augusto Damineli, Claudia V Rodrigues, Matthieu Castro, Carlos EF Lopes, Francisco Jablonski, José D. do Nascimento Jr. and Marildo G. Pereira can be downloaded from The astronomical magazine to iopscience-iop-org-443.webvpn.jxust.edu.cn/article/10.3847/1538-3881/ab0963/pdf. & nbsp