Evidence of a giant planet orbiting a dying white dwarf star has been found. There was previously no example of a planet surviving a star’s transition to a white dwarf, leaving little hope for the fate of our own Solar System.
The evidence for the exoplanet comes in the form of a disc of gas created from its evaporating atmosphere.
Such a system has never been seen before, and it was immediately clear to me that this was a unique star
Dr Boris Gaensicke
The Neptune-like planet discovered is believed to be more than four times the size of the Earth-sized white dwarf that it orbits around.
White dwarfs are approximately 40 times hotter than our Sun, but can significantly shrink to a mere one-hundredth of the size.
Planets continuing to orbit such ex-stars will not receive as much heat as before as the distance between them is larger.
A planet would have to orbit the white dwarf at a distance 75 times closer than the Earth is to the Sun in order for liquid water to exist on its surface.
The discovery was made by astronomers from the University of Warwick’s Department of Physics and the Millennium Nucleus for Planet Formation (NPF) at the University of Valparaiso.
The scientist confirmed this is the first evidence of a giant planet orbiting a white dwarf star.
The star, WDJ0914+1914, was identified in a survey of 10,000 white dwarfs observed by the Sloan Digital Sky Survey.
Researchers estimate the star is approximately 2,000 light years from Earth.
Astronomers at Warwick analysed subtle variations in the light emitted from the system to identify the elements present around the star.
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The scientists detected minute amounts of hydrogen in the data, as well as oxygen and sulphur, which they had never found before.
Using the European Southern Observatory’s Very Large Telescope in Chile they spotted the shape of the gases are typical indicators of a ring of gas.
Lead author Dr Boris Gaensicke, from the University of Warwick, said: “At first, we thought 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 sulphur.
“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 matches what scientists expect for the deeper layers of our own Solar System’s ice giants, Uranus and Neptune.
Dr Matthias Schreiber from the University of Valparaiso calculated the 28,000C hot white dwarf is slowly evaporating this hidden icy giant by bombarding it with high-energy photons.
It is pulling its lost mass into a gas disc around WDJ0914+1914 at a rate faster than 3,000 tonnes per second.
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.”
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