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 RW Aur A creating large amounts of debris that is now falling into, or being "eaten" by the star, temporarily obscuring 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."

RW Aur A is 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 infant planets in the process of forming.

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, or corona, 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.

The dips in both visible light and X-ray emissions led the team to conclude that a dense cloud of gas and dust was obscuring light emissions from RW Aur A.

"We knew about the optical dimming, so we knew that there must be new gas and dust between us and the star," Guenther told Newsweek. "The new X-ray observations measure gas and dust grains and the X-ray absorption is much higher than we expected based on the optical data. That means that the dust is in some way different than usual, maybe it's made up of much larger grains. This ratio is very different from what we see in other young stars."

Furthermore, observations made in 2017 indicated that the disk of gas and dust surrounding the star contained 10 times more iron than in 2013 when the measurements was taken.

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. However, they do note that there is a possibility the excess iron could have come from another source.

"We can think of two ways the inner disk could have that much iron: Either there is a small planet or planetesimal of an Earth-like composition—essentially a large chunk of rock with an iron core—that crashed into something and broke apart and now all the little pieces left over fall into the star," Guenther said. 

Alternatively, the inner edge of the disk could act as a "pressure trap" which captures small pieces of material like dust or iron before being releasing them into the star all at once, although this explanation is less favored by the scientists.

"Both processes have been theoretically predicted, but no star has been caught in the act of accreting this stuff before like RW Aur," he said.

The scientists suggest that previous dimming events at RW Aur A may also have resulted from similar processes.

MIT-Star-Dust_0 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 how infant planets manage to survive, 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 in the statement.

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

This article has been updated to include additional comments from Hans Moritz Guenther.