A Tour of RW Aur A

Narrator (April Jubett, CXC): Since 1937, astronomers have puzzled over the curious variability of a young star named RW Aur A, which is located about 450 light years from Earth. Every few decades, the star's optical light has faded briefly before brightening again. In recent years, astronomers have observed the star dimming more frequently, and for longer periods.

Using NASA's Chandra X-ray Observatory, a team of scientists may have uncovered what caused the star's most recent dimming event: a collision of two infant planetary bodies. Once the planets were destroyed, the debris would have fallen onto the star, generating a thick veil of dust and gas. This would have temporarily obscured the star's light, explaining the dimming astronomers have seen.

Computer simulations have long predicted that planets can fall into a young star, but scientists have never before observed that before now. If this most recent study is correct, it would be the first time that astronomers have directly observed a young star devouring a planet.

Because the X-rays come from the hot outer atmosphere of the star, changes in the X-ray spectrum — the intensity of X-rays measured at different wavelengths — over these three observations were used to probe the density and composition of the absorbing material around the star.

The team found that the dips in both optical and X-ray light are caused by dense gas obscuring the star's light. The observation in 2017 showed strong emission from iron atoms, indicating that the disk contained at least 10 times more iron than in the 2013 observation during a bright period.

The researchers think the excess iron was created when two planetesimals, or infant planetary bodies, collided. If one or both planetary bodies are made partly of iron, their smash-up could release a large amount of iron into the star's disk and temporarily obscure its light as the material falls into the star.

This discovery gives insight into the processes affecting the development of infant planets. Undoubtedly, astronomers will continue to study this fascinating object with Chandra and other telescopes.