spaceSpace and Physics

Hungry Young Stars Change Color When They Eat Their Own Planets


Robin Andrews

Science & Policy Writer

An exoplanet being eaten by its host star. NASA/ESA/G. Bacon

As the old adage goes, you are what you eat. Well, it turns out that this may apply to stars as well, whose planetary diets can cause them to change color. As revealed in a pre-print of a paper uploaded to arXiv, stars gobbling up an iron-rich planet can actually turn a type of reddish-pink – somewhat similar to how a flamingo becomes pinker by eating as many pigment-rich shrimp as it can get its beak on.

In 2015, a team of scientists came to the conclusion that a young iron-rich star in the Gamma Velorum star cluster may have received its ferric (iron) composition by consuming an iron-rich planet or protoplanetary objects. This theory was bolstered when the star was also found to be rich in additional “refractory elements”, those with a high melting point and the type that are normally found on rocky worlds that form relatively close to their host star.


For this new study, a team of researchers at the University of Pisa used computer simulations to determine what happens when planets or other large rocky bodies when they become consumed by the outer layer of a young star, one modeled on the youthful stellar mass from the Gamma Velorum star cluster.

“Unfortunately, the details of the accretion are not known and cannot be directly obtained from the observations,” the team noted in their study. “As such, this work is intended to be a first investigation of the main effects of a single episode of planet ingestion on a star.”

The star-forming region Gum 15, located in the constellation of Vela, the latter of which also contains Gamma Velorum. ESO

As the young star is so small – at around 1.2 to 1.3 times the mass of our Sun – it appears it doesn’t take much to significantly change its chemical composition to a more iron-rich one, perhaps just one or two large rocky worlds. However, there is a caveat to this: it depends on the age of the star.


The closer a star is to its formation, the more extensive and powerful the convection currents within the upper regions of the star will be. This means that any planet that is destroyed and absorbed by the star at this point will have little effect on the overall chemistry, as the iron and other metallic elements will be scattered rather than properly assimilated.

The team’s models indicate that, in order to reproduce the high iron content seen in the young star in the Gamma Velorum cluster, it would have to absorb 53 Earth-like planets if the accretion happened 10 million years after its birth. At 15 million years of age, though, the convection currents are less able to prevent planetary contamination from having a major effect, and only two Earth-sized planets are necessary.

The main visual effect of this increase in metallic elements is that they will absorb shorter wavelength radiation trying to escape from the star into space. This means they will ultimately appear redder, or pinker, depending on how much metal they have absorbed.

Ideally, in order to absolutely confirm this theory, astronomers would have to catch a greedy star in the act of eating its own planets. Unfortunately, as this process happens so remarkably quickly, this search will certainly be anything but easy.


Still, as the study’s authors point out, any star is capable of doing this. Perhaps long ago, in the early days of our own Solar System, our very own Sun snacked on a few unfortunate planets.

(H/T: New Scientist)


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