Chandra X-ray Observatory: evidence of a young star devouring a planet

Chandra X-ray Observatory: evidence of a young star devouring a planet
© illustration: NASA/CXC/M.Weiss X-ray spectrum; NASA/CXC/MIT/H.M.Gunther

Scientists may have observed, for the first time, the destruction of a young planet or planets around a nearby star. Observations from NASA’s Chandra X-ray Observatory indicate that the parent star is now in the process of devouring the planetary debris.

This new discovery made by the Chandra X-ray Observatory gives insight into the processes affecting the survival of infant planets.

Since 1937, astronomers have puzzled over the curious variability of a young star known as RW Aur A, 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.

How was the Chandra X-ray Observatory used?

Using Chandra, a team of scientists may have uncovered what caused the star’s most recent dimming event – a collision of two infant planetary bodies. As the resulting debris fell into the star, it generated a thick blanket of dust and gas, temporarily concealing the star’s light.

Hans Moritz Guenther, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research said: “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.”

The previous dimming events may have been caused by similar collisions of either two planetary bodies or large remnants of past collisions that met head-on and broke apart again.

Previous dips in the stars brightness

RW Aur A is in the Taurus-Auriga Dark Clouds, which host stellar nurseries containing thousands of infant stars. Young stars are still surrounded by a rotating disk of gas and materials ranging in size from small dust grains to pebbles. These disks last for about five 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.

The noticeable dips in the brightness of the star that occurred every few decades each lasted for about a month – until 2011 when the star dimmed again for about six months. The star eventually brightened, only to fade again in mid-2014. In November 2016, the star returned to its full brightness, and then in January 2017 it dimmed again.

The Chandra X-ray Observatory was used to observe the star during an optically bright period in 2013, and then dim periods in 2015 and 2017, when a decrease in X-rays was also observed.

Changes in the X-ray spectrum, over these three observations, were used to probe the density and composition of the absorbing material around the star.

What was found during the observations?

The team found that the dips in both optical and X-ray light are caused by dense gas obscuring the 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.

Researchers suggest the excess iron was created when two planetesimals collided. If one or both planetary bodies are made partly of iron, their collision could release a large amount of iron into the star’s disk and temporarily obscure its light.

The scientists hope to make more observations of the star in the future, to see whether the amount of iron surrounding it has changed — a measure that could help researchers determine the size of the iron’s source.

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