Scientists have first observed the destruction of a young planet or planet around a nearby star. Observations from NASA's Chandra X-ray Observatory indicate that the parent star is devouring the planetary debris. This discovery provides insight into the processes that influence the survival of infant planets.
Since 1937, astronomers have confused the strange variability of a young star called RW Aur A, which is about 450 light-years from Earth. Every few decades, the star's optical light faded briefly before lightening again. In recent years, astronomers have observed that the star dimms more frequently and for a longer period of time.
Using Chandra, a team of scientists might have discovered what caused the star's recent dimming event: a collision of two planetary bodies of infants, including at least one large object is enough to be a planet. As the resulting planetary debris fell into the star, it created a dense dust and gas curtain that temporarily obscured the star's light.
"Computer simulations have long predicted that planets can fall into a young star, but never before observed," says Hans Moritz Günther, a scientist at the Kavli Institute for Astrophysics and Space Research at MIT, who led the study. "If our interpretation of the data is correct, this would be the first time we have directly observed a young star devouring a planet or planets."
The star's previous dimming events may have been caused by similar smashes from both two planetary bodies or large remnants of past collisions that hit head-on and broke apart again.
RW Aur A is located in the dark clouds of Taurus-Auriga, housing stellar nurseries with thousands of young stars. Very young stars, unlike our relatively mature sun, are still surrounded by a rotating disk of gas and lumps of material ranging in size from small dust grains to pebbles and possibly young planets. These discs last about 5 million to 10 million years.
RW Aur A is estimated to be several million years old and is still surrounded by a disk of dust and gas. This star and its binary companion star, RW Aur B, both have the same mass as the sun.
The noticeable drops in the optical brightness of RW Aur A, which occurred every few decades, lasted about a month each. Then, in 2011, the behavior changed. The star was dimmed again, this time for about six months. The star finally brightened to fade again in mid-2014. In November 2016, the star returned to its full brightness, and then dimmed again in January 2017.
Chandra was used to observe the star during a visually bright period in 2013, and then dimly in 2015 and 2017, when a decrease in X-rays was also observed.
As the X-rays come from the star's hot outer atmosphere, the X-ray spectrum changes – the intensity of X-rays being measured at different wavelengths – over these three observations were used to estimate the density and composition of the absorbing material around the star to investigate around.
The team found that the burglaries in both the optical and X-rays are caused by dense gas that obscures the star's light. The observation in 2017 showed a strong emission of iron atoms, suggesting that the disk contained at least 10 times more iron during a light period than the 2013 observation.
Guenther and colleagues suggest that the excess iron is present in two planetesimals or infants was formed planetary body, collided. If one or both planetary bodies are partially made of iron, their decay could release a large amount of iron into the disk of the star and darken its light temporarily as the material falls into the star.
A less preferred explanation is these small grains or particles like iron can be trapped in parts of a disk. If the structure of the disk suddenly changes, such as when the star's partner star passes nearby, the resulting tidal forces can release the trapped particles, creating an excess of iron that can fall into the star.
The scientists hope to make further observations of the star in the future to see if the amount of iron surrounding it has changed – a measure that could help researchers determine the size of the source of iron , For example, if about the same amount of iron appears in a year or two, it may indicate that it comes from a relatively massive source.
"There is a lot of work going on to learn about exoplanets and how they form to see how young planets could be destroyed in interactions with their host stars and other young planets and what factors determine whether they survive," says Günther ,