Regular variations in brightness of young star could be caused by an orbiting planet

New sub-millimeter radio astronomy technology provides window into star and planet formation.
By Laurel Kornfeld | Nov 11, 2017
A variation in the brightness of a young star observed at regular intervals of 18 months could indicate it is being orbited by an as-yet unseen planet.

Observing with the James Clerk Maxwell Telescope (JCMT), which uses new sub-millimeter observation technology, an international team of astronomers discovered the recurring brightening of EC53, which is located in a stellar nursery in the constellation Serpens Main.

The largest single-dish sub-millimeter telescope in the world, JCMT is the product of a partnership between China, Taiwan, South Korea, and Japan. It is approximately halfway through a three-year survey of eight relatively close star-forming regions, aimed at studying brightness variations in young stars.

Understanding these variations will give scientists important insights into the processes of star and planet formation.

Star-forming areas, also known as stellar nurseries, are areas with abundances of molecular gas. Thick gas clouds around young stars make them impossible to see, meaning scientists have to study the clouds' properties to learn about the stars.

The gravity of baby stars pulls gas from the surrounding disk, enabling the stars to grow more massive while releasing energy that heats up the surrounding clouds.

Telescopes capable of observing in sub-millimeter wavelengths can measure the brightnesses of these clouds, which provide details about the young stars.

"This variation in the brightness or twinkle of the star EC53 suggests that something large is disrupting the gravitational pull of the forming star," said Doug Johnstone, Research Officer at the National Research Council of Canada and leader of the survey.

"The fact that it recurs every 18 months suggests that this influence is orbiting around the star--it's quite likely a hidden, forming planet. It is thought that a companion planet is orbiting the star, and its passing gravitational pull disrupts the rate of gas falling onto the forming star, providing a variation in the observed brightness, or light curve, of the star."

While variations in the EC53's brightness were previously observed in near-infrared wavelengths, sub-millimeter observations were necessary to confirm this is happening because gas is accreting onto the star.

Hyungju Yoo, a graduate student at Chungnam National University, and his adviser Jeong-Eun Lee of Kyung Hee University, both in South Korea, made the initial discovery.

"What caught my eye was a new round of data that showed a sudden brightness that hadn't existed in previous observations. I knew that something unique and interesting must be happening around this forming star," Lee emphasized.

The researchers plan to continue monitoring EC53 for the remaining duration of the survey and also look for other young stars with similar brightness variations.

A paper on their findings has been accepted for publication in the Astrophysical Journal.



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