We may have just witnessed a baby star devouring an entire planet

19 Jul 2018

This artist’s illustration depicts the destruction of a young planet, which scientists may have witnessed for the first time. Image: NASA/CXC/M.Weiss

Dimming stars tend to raise an eyebrow or two among astronomers, but one such mystery may be down to a hungry young star’s latest meal.

While Tabby’s star is arguably one of the most famous of the mysterious dimming stars, for nearly a century astronomers have been mystified about the variability of young stars in the Taurus-Auriga constellation found 450 light years from Earth.

In particular, a single star named RW Aur A has been found to be particularly unusual as every few decades its brightness seems to fade before returning once again.

Even weirder is the fact that this dimming has gotten more frequent in the past few years and endures for longer periods. Now, a team of physicists has found a likely, violent answer.

In a paper published to the Astronomical Journal, the researchers put forward evidence that the dimming is the result of the collision of two infant planetary bodies, producing in the chaotic aftermath a dense cloud of gas and dust.

As this material is attracted to its parent star, a thick shroud descends over the star thereby giving it its distinctive dimming.

“Computer simulations have long predicted that planets can fall into a young star, but we have never before observed that,” said Hans Moritz Guenther, 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.”

These findings also suggest that previous dimmings could also have been the result of similar collisions, either from two planetary bodies or the broken remains of past collisions.

‘Where does all this iron come from?’

To observe this, the MIT team used NASA’s Chandra X-Ray Observatory to record x-ray emissions from the star, recording almost 14 hours of data.

This data provided a wealth of information on the star, showing that its disk is far hotter than expected and contains much more iron than expected, as well as a wealth of other material.

The abundance of iron in particular was interesting to the researchers as, usually, an x-ray spectrum of a star shows various elements.

“Here, we see a lot more iron, at least a factor of 10 times more than before, which is very unusual because, typically, stars that are active and hot have less iron than others, whereas this one has more,” Guenther said. “Where does all this iron come from?”

The two leading theories suggest that either this is the result of a phenomenon where small grains of iron become trapped in ‘dead zones’ of a disk, or the more likely theory is that excess iron is created when two planetesimals (or infant planetary bodies) collide, releasing a thick cloud of particles.

“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 said.

Updated, 19 July 2018 at 4.13pm: An earlier version of this article incorrectly stated that the amount of iron detected in the star’s disk was about as much as Earth’s moon. In fact, the moon has far more iron than the scientists estimated in the star’s disk but about the same as a typical moon in our solar system.

Colm Gorey was a senior journalist with Silicon Republic