Astronomers discover an elusive planet responsible for the spiral arms around its star

The Big Eyes Telescope in Arizona. The LBTI instrument combines infrared light from each of the 8.4-meter-diameter mirrors to obtain images of planets and disks around nearby young stars. Credit: Dr. Steele, Big Eyes Telescope Observatory Images of the Milky Way show a rotating pattern of spiral “arms” filled with stars extending outward from the center. Similar patterns have been observed in swirling clouds of gas and dust surrounding some young stars, planetary systems in the process of formation. These so-called protoplanetary disks, which are the birthplaces of young planets, are of interest to scientists because they provide glimpses of what the fledgling solar system might have looked like, and how planets in general might have formed. Scientists have long thought that the spiral arms in these disks could be caused by nascent planets, however none have yet been discovered. In an article published in Natural Astronomy, researchers at the University of Arizona report the discovery of a giant exoplanet, called MWC 758c, that can spawn the spiral arms of the infant planetary system. The astronomers also suggest possibilities for why scientists have had trouble finding this planet in the past, as well as how their methods could be applied to discover other hidden planets in similar circumstances.

“Our study provides strong evidence that these spiral arms are caused by giant planets,” said Kevin Wagner, the paper’s lead author and a postdoctoral researcher at the University of Arizona Steward Observatory. “And with the new James Webb Space Telescope, we’ll be able to do more testing and support this idea by looking for more planets like MWC 758c.” The planet’s star lies about 500 light-years from Earth and is only a few million years old, an embryo compared to our Sun, which is 4.6 billion years old. Therefore, the system still contains a protoplanetary disk, as it takes about 10 million years for circular debris to be ejected from the system, devoured by the star, or formed into planets, moons, asteroids, and comets. . The prominent spiral pattern was in the remains of this system. I first discovered it in 2013, astronomers were quick to point out the connection to theoretical simulations of giant planet formation.

“I think this system is an analogy for what our solar system looks like with less than 1% of its lifespan,” Wagner said. “Jupiter, being a giant planet, probably also interacted with our disk and was sculpted by its gravity billions of years ago, ultimately leading to the formation of Earth.” Most protoplanetary disks have been photographed by astronomers in star systems that can be seen with today’s telescopes. Among some 30 specific tablets, about a third The spiral arms are characteristic: vortices protruding from the interior of the disk and dust particles. Image of a giant planet driving spiral arms in a protoplanetary disk from theoretical simulations. Credit: L. Krapp and K. Kratter, University of Arizona “The spiral arms can provide information about the planet formation process itself,” Wagner said. “Our observations of this new planet support the idea that giant planets form early, accumulating mass from their birth environment, and then gravity alters the environment afterward so that other, smaller planets form.” The spiral arms are generated by the gravitational pull of the companion on matter orbiting the star. In other words, the presence of a massive companion, such as a giant planet, would have been expected to trigger the spiral pattern in the disk. but, previous attempts to detect the planet responsible for it empty noon-until now. “It was an open question as to why we haven’t seen any of these planets yet,” Wagner said. “Most planet formation models indicate that the giant planets must have been very bright soon after their formation, and these planets must have already been detected.”

The researchers were finally able to detect MWC 758c using the Big Eye Interferometer, or LBTI, a UArizona-built instrument that connects the telescope’s two 8.4-meter-diameter primary mirrors and can observe longer wavelengths in the mid-infrared range. , unlike most other mirrors Instruments used to observe exoplanets at shorter or bluer wavelengths. According to Steve Ertel, co-author of the paper and lead instrument scientist at LBTI, the instrument contains a camera that can detect infrared light in a similar way to NASA’s James Webb Space Telescope, or JWST. Although the exoplanet is estimated to be at least twice the mass of Jupiter, it was invisible to other telescopes because of its unexpected red color — the “reddest” planet ever discovered, Ertel said. The longer red wavelengths are more difficult to detect than the shorter wavelengths due to the thermal glow of the Earth’s atmosphere and the telescope itself. LBTI is among the most sensitive infrared telescopes to date and, due to its larger size, may even outperform JWST in detecting planets very close to their stars, such as MWC 758c. “We propose two different models for why this planet shines at longer wavelengths,” Ertel said. “Either this is a planet with a lower temperature than expected, or it is a planet that is still hot from its formation, and is surrounded by dust.” “If there’s a lot of dust around that planet, the dust will absorb shorter wavelengths or bluer light, making the planet appear bright only at longer, redder wavelengths,” said co-author Caitlin Crater, a theoretical astrophysicist at the University of Arizona. . . “In the other scenario of a cooler planet surrounded by less dust, the planet is dimmer and emits more light at longer wavelengths.”

MWC 758 planetary system observed with the Large Eye Interferometer (LBTI) at infrared wavelengths. Theoretical simulations suggest that the newly discovered planet, C, is likely responsible for driving the spiral pattern in the disk of gas and dust surrounding the young star. Credit: K. Wagner et al. Wagner said that the presence of large amounts of dust in the vicinity of the planet may indicate that the planet is still forming and may be in the process of forming a system of moons like Jupiter’s moons around Jupiter. On the other hand, if the planet follows the colder model, there could be something going on in these early star systems that is causing the planets to form cooler than expected, leading planetary scientists to revise planet formation models. planets and exoplanet detection strategies. “Either way, we now know that we need to start looking for reddish protoplanets in these spiral arm systems,” Wagner said. Astronomers hope that once the giant exoplanet is observed with the James Webb Space Telescope, they will be able to judge which of the two scenarios plays out in the infant system. The team was given time to use JWST in early 2024 to complete these observations. “Depending on the results that come from the JWST observations, we can start to apply this new knowledge to other star systems,” Wagner said, “and that will allow us to make predictions about where other planets are hidden and that will give us an idea of ​​what properties we must look for in order to discover them.