X-ray observatory images star eating its planet

Periodic dimming of young star likely caused by debris produced by planets’ destruction.

NASA’s Chandra X-ray Observatory may have caught the first ever image of a star devouring one or more of its orbiting planets.

Located approximately 450 light years from Earth, the young variable star RW Aur A has baffled scientists since 1937 by dimming, then brightening, every few decades. Recently, the dimming has occurred more frequently and lasted for longer durations.

In 2011, the star dimmed for several months, then brightened.  Three years later, in 2014, it dimmed again.  Two years later, it  brightened again until dimming once more in early 2017.

To determine what might be causing the dimming, a team of scientists observed the star with the Chandra telescope when it brightened in 2013 and when it dimmed in 2015 and 2017. They found the dimming corresponded with a decrease in X-ray emission.

X-rays come from a star’s outer atmosphere. By studying changes in the X-ray spectrum emitted by a star, scientists can determine the density and composition of material surrounding the star.

Based on these observations, the researchers determined that RW Aur A, which is very young star and part of a binary system with its companion RW Aur B is devouring planetesimals and possibly even young planets orbiting within its protoplanetary disk of dust and gas.

Interestingly, the two companion stars both have approximately the same mass as the Sun.

Planets and planetesimals that fall into their stars generate debris in the form of heavy layers of gas and dust, which can obscure their stars’ light.

“Computer simulations have long predicted that planets can fall into a young star, but we have never before observed that. If our interpretation of the data is correct, this would be the first time that we directly observe a young star devouring a planet or planets,” said study leader Hans Moritz Guenther of MIT‘s Kavli Institute for Astrophysics and Space Research.

The binary star system is located in the Taurus-Auriga Dark Clouds, a region of abundant stellar nurseries. Estimated to be approximately several million years old, the star, like other very young stars, is still surrounded by a protoplanetary disk of gas and dust.

Material in these disks can range from tiny dust grains all the way through full-fledged planets.

Chandra observations of RW Aur A in 2017 indicated the star was emitting a high level of iron atoms and that the disk surrounding it contained 10 times more iron than it did in 2013.

According to the researchers, the increase in iron was likely produced by a collision of two plantestimals or planets, one or both of which released iron into the disk.

“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 stated.

A paper on the study has been published in the Astronomical Journal.

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