A team of scientists has discovered a highly unusual planetary system comprised of a sun-like star, a dwarf star, and an enormous planet “dancing” in between. The dwarf star and the planet have been gravitationally influencing each other for millions of years. Specifically, the planet’s eccentricity (the amount it deviates from being perfectly circular) and orbital inclination, meaning its angle relative to the equatorial plane of the primary star, have been oscillating back and forth in a process known as Kozai oscillations — and will continue to do so for the foreseeable future. Credit: Timothy Rodigas
A team of scientists has discovered a highly unusual planetary system comprised of a sun-like star, a dwarf star, and an enormous planet sandwiched in between. The planet, first discovered in 2011 orbiting a star called HD 7449, is ~8x Jupiter’s mass and has one of the most eccentric orbits ever found. An eccentric orbit is one that deviates from being perfectly circular. A large eccentricity can indicate that a planet is being affected by other objects nearby. For the planet around HD 7449, the large eccentricity was a clue that something else- something bigger than the known planet -also resided in the system.
“The question was: is it a planet or a dwarf star?” said Timothy Rodigas. To answer the question, Rodigas and his team used the Magellan adaptive optics (MagAO) instrument suite to directly image the mysterious object. MagAO enables astronomers to take extremely high-resolution images, giving them a sharper look at the night sky than ever before. “At the telescope, we saw the object within seconds, and that told us it had to be a dwarf star,” Rodigas added.
Just another boring star, right? No, this one is tiny, only 20% of the mass of the Sun, and its orbit places it close to the primary star, HD 7449A, just 18 astronomical units (AU) away. (1 AU is the distance from the Earth to the Sun.) For comparison, Neptune orbits the Sun at 30 AU.
Not long ago, binaries were thought incapable of hosting planets, but over the past few years the number of circumbinary planets detected has been steadily growing. This system, though, is one of only a handful consisting of a Sun-like star, a dwarf star, and a gas giant planet in between- all within 20 AU. Among these, planet HD 7449Ab is by far the most massive and has the most eccentric orbit.
The dwarf star and the planet have been gravitationally influencing each other for millions of years. Specifically, the planet’s eccentricity and orbital inclination, meaning its angle relative to the equatorial plane of the primary star, have been oscillating back and forth in a process known as Kozai oscillations – and will continue to do so for the foreseeable future.
“It’s difficult to visualize what happens to the planet over time, but you could say that it’s ‘dancing’ between the 2 stars,” Rodigas said.
The team will continue to monitor the system over the coming years using both the radial velocity technique (which measures how stars wobble when planets orbit them), and direct imaging. They hope to determine how such a strange system could have formed. https://carnegiescience.edu/node/1964
Recent Comments