For the first time, scientists have witnessed the dying moments of a solar system that may once have been similar to our own.
Researchers have spotted pieces of an asteroid or rocky planet, similar to those in our own solar system, circling a white dwarf star – the final stage in the life cycle of a star like the sun. The object has fallen toward the star and is now so close that it’s being shredded by the star’s gravity.
“We’re watching the destruction of a solar system,” said Patrick Dufour, a University of Montreal physicist who co-authored the paper describing the research. Dufour is a member of the university’s Institute for Research on Exoplanets.
The paper was published today in Nature.
Like the planet-hunting telescope’s original mission, K2 looks for planets passing in front of their stars, as indicated by a dip in the brightness of the star as the passing planet blocks part of the star’s light. However, since one of the wheels used to point the telescope stopped functioning in 2013, the telescope can only monitor stars in a much smaller field of view.
The white dwarf star WD1145+017 caught the researchers’ eye because it was being dimmed a whopping 40 per cent each time something passed in front of it – something that happened every 4.5 hours.
“Forty per cent is something we’ve never seen for anything,” said Dufour.
It was in fact the first time researchers had ever observed an object passing in front of a white dwarf star, since there aren’t that many of them in Kepler’s field of view.
It appeared that something was orbiting very, very close to the star – at just double the distance between the Earth and the moon, and was proportionally quite large compared to the Earth-sized white dwarf star.
The researchers used ground-based telescopes to make more frequent measurements – once every 30 seconds instead of once every 30 minutes – to get a better idea of the shape of the object orbiting the star.
They found it was in at least six pieces and had a tail, like a comet, suggesting that it was in the process of being shredded by the star’s gravity as it fell closer and closer.
“We think we’re catching it right in the beginning of the process,” Dufour said. “That’s why it’s very rare and very interesting.”
Dust from the object was already falling onto the surface of the star. Dufour analyzed the chemical signatures of the dust visible in the light from the star, and found it was mostly silicon, iron, magnesium and oxygen — suggesting that the orbiting object was once very similar to the asteroids and rocky planets in our own solar system, including Earth.
At least as big as Ceres
The researchers also estimate the object was at least as large as Ceres, the dwarf planet that is the largest object in the asteroid belt between Mars and Jupiter in our own solar system. But it may once have been much larger.
“Maybe part of it has already fallen into the star and sunk,” Dufour suggested.
Scientists had previously seen hints of iron and silicon in dwarf stars (which normally contain only carbon, oxygen, hydrogen and helium) and speculated that those came from planets or asteroids that they were in the process of consuming. But they could never actually see the source.
“This is the first time that we’ve seen that,” Dufour said. “We’re going to learn a lot from this object.”
The researchers think that this star could tell us something about the future fate of the stars and asteroids in our own solar system. One day, the sun will run out of hydrogen and helium fuel, and cool and expand into a red giant.
It will probably consume Earth, Venus and Mercury in the process, but Mars and the asteroids may survive until the red giant shrinks down into a white dwarf. If the events destabilize their orbits and they fall toward the star, they may end up in a situation very similar to the one witnessed around WD1145+017.
A lot of questions remain. Scientists don’t know how long the star has been tearing the object apart or how long the process takes – it could last a year, 10 years or thousands of years, Dufour says.
They plan to keep observing the star for changes over the next few years to see if they can start to figure that out.