Unexpected: Scientists Observing a White Dwarf Make Stumping Find

Astronomers studying white dwarfs have found, for the first time ever, traces of a Neptune-like exoplanet that is evaporating.

Astronomical observations with the Very Large Telescope of the European Southern Observatory (ESO), in Chile, have found, for the first time, evidence of a giant planet orbiting a white dwarf.

Also dubbed a degenerate dwarf, these objects are the stellar core remnants composed mostly of electron-degenerate matter. White dwarfs are extremely dense: their mass can be compared to that of the Sun, while their volumes are comparable to that of Earth.

The newly found planet was discovered orbiting a warm white dwarf at an extremely close range. This has caused the planet’s atmosphere to be swept away from the planet. This unique system suggests how our own Solar System could be in the distant future, according to the researchers published in the journal ‘Nature’.

An artist’s rendering of a white dwarf with a planet (upper right). Image Credit: Mark Garlick.
An artist’s rendering of a white dwarf with a planet (upper right). Image Credit: Mark Garlick.

“It was one of those chance discoveries,” revealed Boris Gänsicke, a researcher at the University of Warwick in the United Kingdom, who led the study.

The team of scientists had examined around 7,000 white dwarfs observed by the Sloan Digital Sky Survey and found that one was distinct from the others. By analyzing subtle fluctuations in starlight, they discovered evidence of chemical elements in amounts that experts had never seen before in a white dwarf.

“We knew that there had to be something exceptional going on in this system, and speculated that it may be related to some type of planetary remnant,” Gänsicke explains.

To get a better view of the qualities of this particular star, called WDJ0914 + 1914, the team analyzed it with the X-shooter instrument at ESO’s Very Large Telescope in the Chilean Atacama desert.

These follow-up observations demonstrated the presence of hydrogen, oxygen, and sulfur associated with the white dwarf.

Upon studying the fine details in the spectra taken by ESO’s X-shooter, the team realized that these elements were in a gas disk that turned towards the white dwarf and did not come from the star itself.

“It took a few weeks of very hard thinking to figure out that the only way to make such a disc is the evaporation of a giant planet,” says Matthias Schreiber from the University of Valparaiso in Chile, who computed the past and future evolution of this system.

Analysis of the data revealed that the amounts of hydrogen, oxygen, and sulfur are similar to those found in the deep atmospheric layers of giant frozen planets such as Neptune and Uranus.

If such a planet were orbiting in close proximity to a hot white dwarf, the extreme ultraviolet radiation emitted from the star would peel away its outer layers and some of this dismantled gas would swirl into a disc, itself accreting onto the white dwarf. And precisely this is what scientists think they have observed around WDJ0914+1914: the first evaporating planet orbiting a white dwarf.

“This is the first time we can measure the amounts of gases like oxygen and sulphur in the disc, which provides clues to the composition of exoplanet atmospheres,” revealed Odette Toloza from the University of Warwick, who developed a model for the disc of gas surrounding the white dwarf.

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