A white dwarf star has been detected ripping an asteroid-like object to shreds. This observation now proves the hypothesis that why a white dwarf star seen to be gaining mass is not fusing heavier elements, but eating its own planets. In about 8 billion years from now, our own sun may do the same thing.
The team of astronomers, led by Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics (CfA), had noticed several planetary pieces in orbit during their observations of the white dwarf (WD 1145+017).
Vanderburg said in a statement:
‘This is something no human has seen before — we’re watching a solar system get destroyed.’
The pieces were detected by the Kepler space telescope. The size of the planetary pieces is estimated to be around the size of the asteroid “Ceres,” which is located inside our own solar system’s main asteroid belt.
These planetary pieces have an orbit of between 4.5 and 4.9 hours, and are too small to be seen. It was the presence of their massive dust clouds, trailing them in their orbits, that helped the researchers detect them.
“It’s fascinating,” Michael Jura, an astronomer from the University of California, Los Angeles, who was not part of the discovery team, told Science Magazine. “They’ve actually caught in the act the process of some asteroid breaking into pieces, being disrupted by the white dwarf host star.”
The white dwarf is about 570 light-years away, and is in the direction of the constellation Virgo. Before becoming a white dwarf, it would have been similar to our own sun. Toward the end of its life, it would have become a red giant, and then thrown off its outer layers.
What remains is an Earth-sized core that’s called a white dwarf star. It then will generally consist of carbon and oxygen with a thin hydrogen or helium shell. Any planets that survived would find life around a white dwarf star very harsh. When a planet or asteroid drifts too close to the dwarf star, the intense tides will rip them to pieces.
For the last decade, we’ve suspected that white dwarf stars were feeding on the remains of rocky objects, and this result may be the smoking gun we’re looking for,” Fergal Mullally, staff scientist of K2 at SETI and NASA’s Ames Research Center in Moffett Field, said in a NASA release.
“However, there’s still a lot more work to be done figuring out the history of this system.”
The typical white dwarf exerts a strong gravitational pull at the surface, which, according to Science Magazine if you were to drop a rock from 1 meter high, it would hit the surface at thousands of miles per hour.
With the gravitational force as strong as this, it is expected that elements heavier than helium should be pulled beneath the star’s surface, but on many white dwarfs there is a presence of heavy elements, which suggests that asteroids are depositing elements such as silicon and iron.
“It’s like panning for gold — the heavy stuff sinks to the bottom. These metals should sink into the white dwarf’s interior where we can’t see them,” John Johnson, a co-author, explained to PHYS ORG.
Boris Gänsicke, an astronomer at the University of Warwick in England who studies heavy-element pollution in white dwarfs, but was not involved in this research, told National Geographic: “These should disappear on relatively short timescales; [because] these elements haven’t disappeared yet means they’ve been replenished relatively recently.”
Francesca Faedi, an astronomer from University of Warwick, wrote in a commentary that accompanies the study: “Future observations of evaporating planets and metal-polluted white dwarfs might even allow scientists to distinguish between material that originated in a planet’s core as opposed to its mantle.”
Scientists have said that white dwarfs that showed evidence of heavy metals had become “polluted” as they destroyed asteroids or rocky planets, but they had little to no evidence, and most of what they had was often circumstantial. Few white dwarfs that are polluted show any signs of having debris disks surrounding them, and for the ones that do, their origin has been uncertain.
This system however shows all three: A polluted white dwarf, a surrounding debris disk, and at least one compact, rocky object.
‘We now have a ‘smoking gun’ linking white dwarf pollution to the destruction of rocky planets,’
While there will be other interpretations of these observations, Gänsicke says that Vanderburg’s group is plausible. “I can’t think of an alternative explanation,” he says. “The exciting thing is that, yes, the story we’ve been developing over the past decade works the way we think it works.”
The Harvard-Smithsonian Center for Astrophysics wrote in a press release: “What is certain is that the remaining objects will not last forever. They are being vaporized by the intense heat of the white dwarf. They also are orbiting very close to the tidal radius, or distance at which gravitational tides from the white dwarf can rip apart a rocky body.
“Within the next million years or so, all that will remain of these asteroidal bits is a thin metal dusting on top of an innocent-looking white dwarf star.”
The origin of the objects orbiting the white dwarf star is still unknown, but it is likely that it was an existing planet whose orbit had become unstable when it was dragged towards the white dwarf. There are up to six dwarf planets in orbit around the star that have been spotted, each having a trailing dust field of debris.