For the first time ever, researchers have discovered a huge planet orbiting a white dwarf star. They used ESO’s Very Large Telescope.
About 1200 light-years from Earth, a giant planet orbits the remnant of an exploded star – a white dwarf – a quarter of its size about once every ten days. This is the first time scientists have seen an entire planet orbiting a white dwarf.
Astronomers from the University of Warwick’s Department of Physics and the Millennium Nucleus for Planet Formation (NPF) at the University of Valparaíso published their discovery today (4 December) in the journal Nature.
Until now, scientists had never seen a planet that has survived a star’s transition to a white dwarf.
The researchers found the star, WDJ0914+1914, during a survey of 10,000 white dwarfs observed by the Sloan Digital Sky Survey. Scientists at Warwick analyzed subtle variations in the light emitted from the system to identify the elements around the star.
The giant planet was discovered through the disc of gas created by its evaporating atmosphere. The gas disc contains hydrogen, oxygen, and sulfur. That mixture most likely came from the planet, whose atmosphere is being evaporated by radiation from the white dwarf.
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Using the Very Large Telescope of the European Southern Observatory in Chile they found the shape of the gas is a typical indicator of a ring of gas.
Observations also revealed the gas disc was swirling into the white dwarf, and not coming from the star itself.
Lead author Dr. Boris Gaensicke, from the University of Warwick, said: “At first, we thought that this was a binary star with an accretion disc formed from mass flowing between the two stars.
“However, our observations show that it is a single white dwarf with a disc around it roughly 10 times the size of our sun, made solely of hydrogen, oxygen, and sulfur.
“Such a system has never been seen before, and it was immediately clear to me that this was a unique star.”
Analysis of the data suggests the composition of the disc is similar to that found in the deep atmospheric layers of icy, giant planets like Neptune and Uranus.
Calculations show the 28,000°C hot white dwarf is pulling the planet’s lost mass into a gas disc around the star at a rate of more than 3,000 tonnes per second.
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Dr. Gaensicke said: “This star has a planet that we can’t see directly, but because the star is so hot it is evaporating the planet, and we detect the atmosphere it is losing.
“There could be many cooler white dwarfs that have planets but lacking the high-energy photons necessary to drive evaporation, so we wouldn’t be able to find them with the same method.
“This discovery is major progress because over the past two decades we had growing evidence that planetary systems survive into the white dwarf stage.
“We’ve seen a lot of asteroids, comets and other small planetary objects hitting white dwarfs, and explaining these events requires larger, planet-mass bodies further out.”
Matthias Schreiber from the University of Valparaiso in Chile, who computed the past and future evolution of this system said: “In a sense, WDJ0914+1914 is providing us with a glimpse into the very distant future of our own solar system.”
Once the Earth’s sun runs out of fuel in about 4.5 billion years it will shed its outer layers, destroying Mercury, Venus, and probably the Earth, eventually leaving behind the burnt-out core – the white dwarf.