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The search for exoplanets (planets orbiting stars located beyond the limits of our solar system) is a hot topic in astrophysics.
Of the various types of exoplanets, one is hot in the literal sense: hot Jupiters, a class of exoplanets that are physically similar to the gas giant planet Jupiter in our neighborhood.
Unlike “our” Jupiter, Hot Jupiters orbit very close to their starscomplete a full orbit in just a few days or even hours and, as their name suggests, have extremely high surface temperatures. They have great fascination for the astrophysics community. However, they are difficult to study because the glare from the nearby star makes them difficult to detect.
Now in a studio published today in Nature Astronomy, Scientists report the discovery of a system formed by two celestial bodies, located about 1,400 light years away, which together offer an excellent opportunity to study Jupiter’s hot atmospheres, as well as to advance our understanding of evolution planetary and stellar.
The discovery of this binary system – the most extreme of its kind known so far in terms of temperature – was made through the analysis of spectroscopic data collected by the Very Large Telescope of the European Southern Observatory in Chile.
“We have identified a hot object similar to Jupiter that orbits a star and that is the hottest ever found, about 2,000 degrees hotter than the surface of the Sun,” says the lead author of the study, Dr. Naama Hallakoun, postdoctoral researcher associated with Dr. Sagi Ben-Ami’s team in the Department of Particle Physics and Astrophysics at the Weizmann Institute of Science.
He adds that, unlike hot Jupiter planets obscured by glare, it is possible to see and study this object because it is so large compared to the host star it orbits, which is 10,000 times fainter than a normal star. “This makes it a perfect laboratory for future studies of the extreme conditions of hot Jupiters,” he says.
Hallakoun’s new discovery, an extension of the research he carried out in 2017 with Professor Dan Maozhis doctoral advisor at Tel Aviv University, may provide a clearer understanding of hot Jupiters, as well as the evolution of stars in binary systems.
The binary system that Hallakoun and his colleagues discovered is made up of two celestial objects, both called “dwarves”, but they are very different in nature. One is a “white dwarf” the remnant of a Sun-like star after it has exhausted its nuclear fuel. The other part of the pair, which is neither a planet nor a star, It is a “brown dwarf”, a member of a class of objects that have a mass between that of a gas giant like Jupiter and a small star.
Brown dwarfs are sometimes called failed stars because they are not massive enough to drive hydrogen fusion reactions. However, unlike gas giant planets, brown dwarfs are massive enough to survive the “pull” of their stellar companions.
“Stars’ Gravity Can Cause Objects That Get Too Close to Fall Apartbut this brown dwarf is dense, with 80 times the mass of Jupiter compressed into the size of Jupiter,” says Hallakoun. “This allows it to survive intact and form a stable binary system.”
When a planet orbits very close to its star, the differential forces of gravity acting on the near and far side of the planet can cause the planet’s orbital and rotational periods to become synchronized. This phenomenon, called “tidal locking,” permanently locks one side of the planet in a position facing the star, similar to how Earth’s Moon always faces Earth, while its so-called “dark side” remains. out of sight. Tidal locking leads to extreme temperature differences between the “dayside” hemisphere bombarded by direct stellar radiation and the other hemisphere, the “night side”, which faces outward and receives a much smaller amount of radiation.
The intense radiation from their stars causes extremely high surface temperatures on hot Jupiters, and calculations Hallakoun and his colleagues made on the white dwarf-brown dwarf system show just how hot things can get.
By analyzing the brightness of the light emitted by the system, they were able to determine the surface temperature of the brown dwarf that orbits in both hemispheres. They discovered that The dayside has a temperature of between 7,250 and 9,800 Kelvin (approximately 7,000 and 9,500 Celsius)which is as hot as a type A star (Sun-like stars that can be twice as massive as the Sun) and hotter than any known giant planet. The temperature of the night side, on the other hand, is between 1,300 and 3,000 Kelvin (approximately 1,000 and 2,700 Celsius), resulting in an extreme temperature difference of about 6,000 degrees between the two hemispheres.
Hallakoun says the system she and her colleagues discovered offers an opportunity to study the effect of extreme ultraviolet radiation on planetary atmospheres.
Such radiation plays an important role in a variety of astrophysical environments, from star-forming regions, through the primordial gas disks from which planets form around stars, to the atmospheres of the planets themselves. This intense radiation, which can cause evaporation of gases and the breakdown of moleculescan have a significant impact on both stellar and planetary evolution. But that’s not all.
“Barely a million years have passed since the formation of the white dwarf in this system – a minuscule amount of time on the astronomical scale – and we have been able to take a rare look at the early days of this type of compact binary system,” says Hallakoun. He adds that while the evolution of individual stars is fairly well known, the evolution of interacting binary systems is still poorly understood.
“Hot Jupiters are the antithesis of habitable planets: they are extremely inhospitable places for life. Future high-resolution spectroscopic observations of this hot Jupiter-like system (ideally made with NASA’s new James Webb Space Telescope) may reveal how warm, highly irradiated conditions affect atmospheric structure, something that could help us understand exoplanets in other parts of the universe,” concludes Hallakoun.
Study participants also included Prof. Dan Maoz of Tel Aviv University; Dr. Alina G. Istrate and Prof. Gijs Nelemans from Radboud University, The Netherlands; Prof. Carles Badenes of the University of Pittsburgh; Dr. Elmé Breedt of the University of Cambridge; Prof. Boris T. Gänsicke and the late Prof. Thomas R. Marsh of the University of Warwick; Prof. Saurabh W. Jha of Rutgers University; Prof. Bruno Leibundgut and Dr. Ferdinando Patat of the European Southern Observatory; Dr. Filippo Mannucci of the Italian National Institute of Astrophysics (INAF); and Prof. Alberto Rebassa-Mansergas from the Polytechnic University of Catalonia.
The research of Dr. Sagi Ben-Ami, holder of the Aryeh and Ido Dissentshik Career Development Chair, is supported by the Peter and Patricia Gruber Award; the Azrieli Foundation; the André Deloro Institute for Advanced Research in Space and Optics; and the Willner Family Leadership Institute for the Weizmann Institute of Science.
