Cosmic Appetite

Recently acquired X-ray data may be first evidence of a star devouring a planet and might explain its mysterious dimming.

- Jennifer Chu

For nearly a century, astronomers have puzzled over the curious variability of young stars residing in the Taurus-Auriga constellation some 450 light years from Earth. One star in particular has drawn astronomers’ attention. Every few decades, the star’s light has faded briefly before brightening again.

In recent years, astronomers have observed the star dimming more frequently, and for longer periods, raising the question: What is repeatedly obscuring the star? The answer, astronomers believe, could shed light on some of the chaotic processes that take place early in a star’s development.

Now physicists from MIT and elsewhere have observed the star, named RW Aur A, using NASA’s Chandra X-Ray Observatory. They’ve found evidence for what may have caused its most recent dimming event: a collision of two infant planetary bodies, which produced in its aftermath a dense cloud of gas and dust. As this planetary debris fell into the star, it generated a thick veil, temporarily obscuring the star’s light.

“Computer simulations have long predicted that planets can fall into a young star, but we have never before observed that,” says Hans Moritz Guenther, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research, who led the study. “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 star’s previous dimming events may have been caused by similar smash-ups, of either two planetary bodies or large remnants of past collisions that met head-on and broke apart again.

“It’s speculation, but if you have one collision of two pieces, it’s likely that afterward they may be on some rogue orbits, which increases the probability that they will hit something else again,” Guenther says.