'Planet engulfing' star 350 light years from Earth

'Planet engulfing' star 350 light years from Earth



A star that devours planets has been discovered by researchers who believe it could have already eaten 15 of them.

The planet-gobbling star Kronos and its sister Krios are both around 4 billion years old and are around 350 light years from Earth.

Dubbed Kronos after the child-eating Titan of Greek mythology, the star is the clearest and most dramatic case yet of a sun-like star consuming its own planets.



'Even if our sun ate the entire inner solar system, it wouldn't come close to the anomaly we see in this star,' said study co-author David Hogg, group leader for astronomical data at the Center for Computational Astrophysics (CCA) at the Flatiron Institute.

Future surveys of the gluttonous star's planetary system could provide new insights into how solar systems form and evolve, according to Semyeong Oh, an astrophysicist at Princeton University.

Binary stars are typically near-identical twins.

Kronos and Krios, however, have vastly different chemical makeups, including the largest difference in metal content of any binary system yet studied.

'We started discussing what could make two stars that must have been born together have such different chemistry now,' Dr Oh said.

The compositional differences between Kronos and Krios are most pronounced for elements such as iron, silicon, magnesium and lithium — metals that make up the bulk of rocky planets such as Earth.



Because these elements are concentrated in Kronos's outer layers, rather than mixed throughout the star itself.

The researchers conclude that the star probably consumed many planets' worth of rocky material a billion years or more after its formation.

They added material altered the composition of Kronos's outer layers relative to its sibling star.



From the data, the researchers estimate that Kronos has gulped 15 Earth masses; by comparison, our entire inner solar system contains roughly two Earth masses of rocky material.

The exact process that led Kronos to devour its inner planets remains unknown, but the researchers suggested several theories.

The leading one is that Kronos and Krios once flew too close to another star, which stretched out the orbits of Kronos’ outermost planets.

This caused the outer planets to move through the inner solar system, in turn catapulting the rocky inner planets into death-spiral orbits.

But this theory would require that Krios managed to somehow avoid a similar doomsday scenario. 

Previous studies presented similar evidence of planet eating in other types of stars such as white dwarfs and even our own sun, but never to such an extreme.

Kronos's twin Krios evidently either remained far enough away from other stars so that its planetary system remained unaffected or had fewer rocky planets to consume.

They orbit each other infrequently, on the order of every 10,000 years or so and their official designations are HD 240430 and HD 240429.

The work also reveals a potential window into how solar systems change over time, says study co-author Adrian Price-Whelan.

'We assume that once stars are born, their chemistries are fixed,' he said.

'This is yet more evidence of stars changing.'