A Giant Planet Has Been Spotted Around A White Dwarf For The First Time

This illustration shows the white dwarf WDJ0914+1914 and its Neptune-like exoplanet. ESO/M. Kornmesser

An international group of astronomers has discovered the first gas giant planet orbiting a hot white dwarf. The planet is orbiting at such close range it's evaporating leaving distinct chemical traces around the star, which is how astronomers were able to identify its presence.

White dwarfs are the core remnants of stars like the Sun. When these stars turn into red giants, they begin to shed their outer layers, eventually leaving behind a dense core, becoming a white dwarf. These are often surrounded by disks of material made up of debris of planetesimals and the leftover gas of the star's atmosphere.

A team led by Boris Gänsicke from the University of Warwick, UK inspected around 7,000 white dwarfs from the Sloan Digital Sky Survey and found one like no other. As reported in Nature, they found unusual chemical signatures for WDJ0914+1914. Follow-up observations, using ESO’s Very Large Telescope, confirmed the presence of hydrogen, oxygen, and sulfur and, more excitingly, that the emission was coming from the disk around the star. Based on the chemicals detected, the team realized that the powerful ultraviolet emission from the star was ripping atoms from the atmosphere of a Neptune-like planet.

“It was one of those chance discoveries,” lead author Professor Gänsicke said in a statement. “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.”

The gas giant is located about 10 million kilometers (6 million miles) from the star and makes its way around the orbit in just 10 days. The star has a temperature five times that of the Sun, so it's literally cooking the planet because it is so close to it. This proximity constantly erodes the planet’s atmosphere and about 3,000 tons of this material finds its way into the disk.

“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,” added co-author Dr Odette Toloza, also from the University of Warwick.

White dwarfs have no internal mechanism that produces energy, no nuclear fusion or the like. They start as a hot ball of degenerate matter and slowly cool down. This is the fate that awaits WDJ0914+1914 in about 350 million years. At that point, it will be cool enough to no longer affect the planet. The planet will likely still be around then. If we consider it has the mass of Neptune, it will have lost only 4 percent of its mass.

The team also thinks that there is more than meets the eye in this system. The unusual location of this planet so close to its star is likely to do with the gravitational influence of other planets in the system.

As always, there is more work to do studying this system and other white dwarfs. The European Gaia satellite has discovered 260,000 white dwarfs so far and the team believes that among them a couple of dozen will have planets just like this one.

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