Stars are amazing; from their creation and all through their lifespan they represent beauty, power and mystery. Stars also like to go out with a bang, literally. At the end of a star's life they make their own funeral pyre, throwing off most of their remaining gas in a glorious last display of their immense power and leaving behind a dense, cinder-like core known as a white dwarf.
In a paper published Friday in Science, a team led by Christopher Manser of the University of Warwick in England reports unprecedented observations of a white dwarf slightly larger than Earth but containing almost the mass of the sun-called SDSS J1228+1040. "It's like the iron core left behind by a larger body that's been ripped apart," Manser says. "The crust and mantle have come off this body. We're left with this iron core orbiting around that has a high internal strength holding it together, not just gravity."
The white dwarf's three-million-kilometer-wide debris disk was first discovered more than 15 years ago, making the star one of fewer than a dozen white dwarfs known to be surrounded by disks. When a star of less than about eight solar masses exhausts its hydrogen fuel, it expels its outer layers, engulfing any close-in planets in the process. And although more than 4,000 exoplanets have been discovered to date, scientists have only once before seen smoking-gun evidence of this process: the remains of a planet in a disk around the white dwarf WD 1145+017, which was closely studied in 2015.
Whereas those planetary remnants orbit around WD 1145+017 in 4.5 hours, the heavy-metal core circling SDSS J1228+1040 completes a revolution in less than half of that time. The new study's authors detected the star's dense companion using the 10.4-meter Gran Telescopio Canarias (GTC) on the Canary Islands in two separating observing periods in April 2017 and in April and May 2018, respectively.
Perhaps, however, similar objects await discovery around other white dwarfs. Whether studying them individually or in multitudes, such heavy-metal worlds may offer grim previews of our own solar system's future, when our sun's fuel runs out some five billion years hence. "It's really exciting, because this is sort of the missing piece, if you like, [of white dwarf planetary systems]," says Sarah Casewell of the University of Leicester in England, who was not involved in the research. "We know big things can survive, and we know tiny things get destroyed. This is quite a sizable rocky object that has survived."
