This Tiny White Dwarf Star is Evaporating an 'Ice Giant' Exoplanet
Somehow, a planet survived the devastating explosion of a star's death, and the scorching white dwarf star that remains is now steadily evaporating this much-larger icy exoplanet. According to CNN, this first-ever sighting is what researchers say is "one of those chance discoveries."
Star WD J0914+1914 is located near the constellation Cancer and was once a Sun-like star (or yellow dwarf). When these stars burn through their fuel, they expand into red giants and destroy nearby planets as they inflate. Eventually, these red giants collapse into white dwarfs, which are extremely small and extremely hot. Star WD J0914+1914 is approximately the size of Earth.
Scientists noticed the star when they were scanning a high number of white dwarfs with the Sloan Digital Sky Survey (as part of a larger project to create a 3D map of the universe). They were studying the light emitted by the white dwarfs to analyze their elements and noticed this one kept spiking in hydrogen, oxygen, and sulfur. Oxygen and sulfur had never been seen near white dwarfs before, so they took a closer look.
"…Our observations show that it is a single white dwarf with a disk around it roughly ten 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," said lead researcher Boris Gaensicke from the University of Warwick.
The planet orbiting it is roughly four times the size of star WD J0914+1914 (or four times the size of Earth). It is classified as an ice giant – a type of planet made of ice and cold heavy gases much like Neptune. Scientists couldn't directly observe the planet but, based on the disc of gas they observed, they were able to deduce that the star's extreme heat is steadily evaporating the gas giant.
"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," Gaensicke explained.
The planet's current orbit would actually place it inside the star during its red giant phase; scientists believe that the planet moved closer when the star lost much of its mass during the transition from a red giant to a white dwarf.
Gaensicke concluded, "This discovery is major progress because over the past two decades we had growing evidence that planetary systems survive into the white dwarf stage."
The study was published on Wednesday in the journal Nature.