The corpse of a long-dead star surprises astronomers by eating a planet

A dead star core about 145 light-years away in space is doing anything but resting in peace. 

Astronomers have learned that this white dwarf, the remnant of a medium-size star after running out of nuclear fuel, has gobbled up a rocky planet from its former system. The weird part: This white dwarf isn't newly deceased but has been a corpse for about 3 billion years. 

The star remnant, called LSPM J0207+3331, demonstrates that even very ancient planetary systems don't become cosmic ghost towns after their host stars perish, but remain active for a long time after, challenging assumptions about the end stages of a star, including those to come for our own sun.

A dead star that no longer generates fusion doesn't cease to influence its surroundings, John Debes, a co-investigator of the study at the Space Telescope Science Institute in Baltimore, explained to Mashable. Though its temperature gradually cools, its gravity remains.

"White dwarfs are truly like the dying coals after a fire," Debes said. "For many billions of years, (the remnant) still emits light and radiation, which no doubt have an effect." 

Despite the white dwarf's age, it has a disk of debris chock-full of heavy elements. This material is evidence that something rocky — a dwarf planet like Pluto, moon, or an asteroid — was recently reeled in and torn apart, according to the study, which appears in The Astrophysical Journal Letters.

Using the W. M. Keck Observatory in Hawaii, researchers detected 13 different chemical elements in the white dwarf’s atmosphere — including iron, nickel, silicon, and calcium — that don’t belong there. The chemical mix looks similar to that of Earth, except with a pinch of iron and nickel. The findings suggest the star consumed a small world about 120 miles wide with a large metallic core, possibly even larger in proportion than Earth’s, the authors said.

The W.M. Keck Observatory, the twin domes on the left, detected 13 different chemical elements in the white dwarf's atmosphere that don't belong there. Credit: Toni Salama / Chicago Tribune / Tribune News Service via Getty Images

The most likely explanation for this is that some kind of disturbance — perhaps a gravitational nudge from another planet — knocked the little world out of its orbit in the past few million years, they said, causing it to spiral toward the white dwarf and meet its demise.

It's highly unusual to find so much rocky material around an old white dwarf, said Patrick Dufour, a coauthor from the Université de Montréal, especially one with a hydrogen-rich atmosphere. Until now, nearly all white dwarfs showing this kind of contamination had helium-dominated atmospheres, where heavy elements are easier to spot. 

The new results show that even cool, hydrogen-rich white dwarfs, which make up the bulk of known white dwarfs, can gather and feast on planetary debris for billions of years.

The researchers think hidden worlds the size of Jupiter may be orbiting the white dwarf, shaking up the system from afar. These giant exoplanets would be hard to see directly because they’re cold and distant, but future observations from telescopes such as the European Space Agency's Gaia and NASA’s James Webb Space Telescope could try to find them.

Scientists are interested in LSPM J0207+3331 because, in its past life, it wasn't just any star but one not too dissimilar from our own. Studying it may shed light on the final act for our solar system, in about 5 billion years after the sun dies. 

"We definitely are seeing that planetary systems are active and have so much to tell us at all life stages of a star," Debes said. "It opens the interesting possibility that our own solar system will have an active and interesting life beyond when our own sun turns into a white dwarf."