A HEAVY-METAL PLANET ORBITING A DEAD STAR CAN PREDICT THE END OF OUR WORLD

Heavy-metal worlds will deliver bleak predictions of the future of our own solar system, when the fuel of our sun runs out about five billion years from now.

By Balthazar Malevolent

A HEAVY-METAL PLANET ORBITING A DEAD STAR CAN PREDICT THE END OF OUR WORLD

When most of the stars reach the end of their lives, they make their own funeral pyre, throwing away much of their remaining gas in a triumphant last show of their tremendous strength and leaving behind a dark, cinder-like core known as a white dwarf. But what will become with those planets that orbit such a star? This question has been hard to address, but now scientists believe they have found the possible remains of a world of white dwarf, a first-of-its-kind finding that may bring fascinating insights into the final days of planetary systems all over the universe.

In this artist’s rendition, the remnant core of a planet orbits in a debris disk around the white dwarf star SDSS J1228+1040.

A team led by University of Warwick's Christopher Manser in England announced unprecedented observations of a white dwarf star slightly larger than our planet but containing almost the whole mass of the sun. Called SDSS J1228 + 1040, the star is located about 410 light-years away, and is more specifically known as a "polluted" white dwarf, astronomers can detect raining on its surface because of the heavy elements of it. It is believed that that material originates from a gas disk which surrounds the object. And within that disk, they have found ghostly remains of a planet.

"This is like the iron core left behind by a larger body torn apart," says Manser. "The body has come off the crust and mantle. We're left with the iron core rotating around which has a strong internal strength that keeps it together, not just gravity.

The researchers have detected the dense companion of the star using the Canary Islands' 10.4-meter Gran Telescopio Canarias (GTC) in two separate observation periods in April 2017, and in April and May 2018 respectively. By dividing the light emitted by the white dwarf into its constituent wavelengths — as a prism divides white light into a rainbow — the team detected the disk and reported color changes corresponding to its orbital movement.

This method is generally used to study star systems such as SDSS J1228 over the long period of time, but by following this white dwarf over several hours, the team discerned a clump of material inside the disk that displayed a shift that was entirely their own. The strength of the shift suggested that its source was a firm object approximately 600 kilometers across — a planetary core, with a density between 7.7 and 39 gpcc, comparable to the pure iron found within the core of Earth. "The density of the piece of rock is consistent with what we think is the core of planets are," reports Luca Fossati from the Austrian Academy of Sciences. "That's fine. It generally confirms the idea we have that these dust and debris disks are [the remains of] ancient planets that orbit around some of the white dwarfs."

Similar objects might, however, await discovery around other white dwarfs. Either researching them individually or in multitudes, these heavy-metal worlds will deliver bleak predictions of the future of our own solar system, when the fuel of our sun runs out about five billion years from now. "It's really exciting, because it's sort of the missing element, if you like, [of planetary white dwarf systems]," says Sarah Casewell of Leicester University in England, who was not involved in the study. "We know that big things will survive and we know that small things get killed. This is a fairly large rocky object that has survived.

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