Nasa's X-ray Observatory Spots Hungry Star Devouring a Young Planet, in Scientific First

Scientists think they have observed a star in the process of devouring a young planet, or planets, in what may be a scientific first.

The hungry star, known as RW Aur A, is located around 450 light-years from Earth. It has long puzzled researchers because, every few decades, its light fades briefly before brightening again. In recent years, these dimming periods have occurred more frequently and lasted for longer.

Using data collected by NASA’s Chandra X-ray Observatory—an extremely sensitive space observatory that detects X-rays—a team of scientists may have found an explanation for the star’s most recent dimming event in 2017.

The evidence suggests that two infant planetary bodies collided near to the star causing debris to fall into it, generating a thick cloud of dust and gas that temporarily obscured its light, according to a study published in The Astronomical Journal.

"Computer simulations have long predicted that planets can fall into a young star, but we have never before observed that," Hans Moritz Guenther, research scientist at MIT's Kavli Institute for Astrophysics and Space Research and lead author of the study, said in a statement. "If our interpretation of the data is correct, this would be the first time that we have directly observed a young star devouring a planet or planets."

The scientists suggest that previous dimming events may also have resulted from similar collisions of planetary bodies or smaller debris.

RW Aur A is thought to be a very young star, likely just a few million years old. Typically, stars at this stage of their lifecycle are surrounded by a rotating disk of gas and material ranging in size from small dust grains right up to miniature planets in the process of forming.

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Observations made with Chandra over a five-year period—which included a brightening event in 2013, followed by two dimming events in 2015 and 2017—enabled the scientists to determine what type of material is present in the disks

The observatory picked up X-rays emitted by the hot outer atmosphere of RW Aur A that changed in intensity over the three measurements—much like the dimming and brightening events seen in the visible light observations from the star— allowing the team to work out the density and composition of the surrounding material.

These dips in both visible light and X-ray emissions led the team to conclude that a dense gas was obscuring light emissions from RW Aur A. Furthermore, the observation in 2017 indicated that the disk contained 10 times more iron atoms than the 2013 observation.

The authors suggest that this excess iron indicates that two infant planetary bodies—of which one or both was made partly of iron—collided, releasing large amounts of the metal into the star’s disk and temporarily obscuring its light as material fell into RW Aur A. However, they do note that there is a possibility the excess iron could have come from another source.

This artist’s illustration depicts the destruction of a young planet, which scientists may have witnessed for the first time. NASA/CXC/M.Weiss

The latest findings shed new light on the processes that affect the survival of infant planets, according to the researchers.

"Much effort currently goes into learning about exoplanets and how they form, so it is obviously very important to see how young planets could be destroyed in interactions with their host stars and other young planets, and what factors determine if they survive," Guenther said.

The next step for the scientists is to try and determine whether the amount of iron surrounding the star has changed, which could reveal the size of the iron’s source.

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