For the first time, a team of astronomers has found circumspect evidence of a giant planet orbiting a white dwarf star, which is 1,200 light-years from Earth, and is more than four times the size of Earth, the first planet to orbit a white dwarf star; A comet-like gas tail is being evaporated by the hot white dwarfs it orbits; in other hot white dwarfs, traces of “evaporating” giant planets may be common.
A giant planet spins around a white dwarf star Picture: MARK GARLICK
Researchers at the University of Warwick and other institutions have discovered a mysterious cloud of gas around a white dwarf using the European Southern Observatory’s (ESO) telescope. The disk contains a mixture of hydrogen, oxygen and sulfur that is most likely from the planet. This is the first time researchers have found evidence of giant planets linked to white dwarfs.
White dwarfs are remnants of solar-like stars, and at close range, the atmosphere of the giant planet is stripped off, forming a gas disk around the white dwarf. This unique system hints at what the solar system might look like in the distant future. The paper was recently published in Nature.
“This is an accidental discovery,” said Boris Nsicke of the University of Warwick, who led the study. “
White dwarfs evolved from some stars. Some stars of similar mass to the sun first expand into red giants when their fuel runs out, and eventually evolve into a white dwarf. So far, there is no evidence that planets survived the transformation of stars into white dwarfs.
The white dwarf, known as WDJ0914-1914, seems unusual.
The team examined about 7,000 white dwarfs observed by the Sloan Digital Survey and found that one of them was different from the others. By analyzing subtle changes in light from the star, they found trace amounts of chemical elements, the number of which scientists had never seen on a white dwarf before.
They found very small hydrogen spikes in the data, as well as oxygen and sulfur spikes, which had never been seen before.
“We think there must be something unusual in this galaxy, and speculate that it may be related to some type of planetary remains. Nsicke told China Science Daily.
To better understand the characteristics of WDJ0914-1914, the team analyzed it using an X-ray transmitter on the Verycama Desert Very Telescope in Chile. By studying spectral details, the team found that the elements were rotated from a gas disk into the white dwarf, not from the star itself.
Matthias Schreiber of the University of Valparaiso in Chile calculates the past and future evolution of the system. “It took us a couple of weeks to think hard and finally figure out that the only way to make such a disk was to have a huge planet evaporate. Schreiber said.
If there were this planet, it would be the first known “survivor” to experience stellar decay.
The researchers found that the levels of hydrogen, oxygen and sulfur detected were similar to those found in the deep atmospheres of giant frozen planets such as Neptune and Uranus. If such a planet orbits near a hot white dwarf, extreme ultraviolet radiation from the white dwarf will strip its outer layer, and some of the stripped gas vortex will form a disk and accumulate onthe white dwarf.
That’s what scientists saw around WDJ0914 and 1914, about 1,500 light-years from Cancer, an evaporating planet that rotates around a white dwarf. Previously, scientists had never found evidence of giant planets around white dwarfs. This may be the first of many such stars in orbit.
By combining observational data with theoretical models, a team of astronomers from the UK, Chile and Germany were able to paint a clearer picture of this unique system.
White dwarfs are small and very hot, with temperatures as high as 28,000 degrees Celsius, five times the temperature of the sun. By contrast, the planet is cold and huge, and it orbits the white dwarf at close range, orbiting it for a week in 10 days. High-energy photons from white dwarfs are gradually evaporating the planet’s atmosphere. Most of the gas escapes, but some are sucked into a disk, spinning into the white dwarf at a rate of 3,000 tons per second. It is this disk that makes the originally hidden planets visible.
“This is the first time that the number of gases such as oxygen and sulfur in the disc has been measured, providing clues to the study of the composition of the atmospheres of exoplanets,” said Odette Toloza of the University of Warwick. Toloza has developed a model for calculating gas disks around white dwarfs.
“This discovery also opens a new window into the ultimate fate of planetary systems. Nsicke said.
4.5 billion years later
The planet orbits the white dwarf, just 10 million kilometers away, 15 times the radius of the white dwarf, which was supposed to be deep inside when it became a red star. The planet’s unusual location means that the planet is closer to it at some point after the main star becomes a white dwarf.
The researchers believe the new orbit may be the result of gravitational interactions with other planets in the system, meaning that more than one planet may have survived a dramatic shift in its host star.
In a sense, WDJ0914 and 1914 offer a glimpse into the distant future of the solar system. “The white dwarf we see today was once a star similar to the sun. Schreiber told reporters.
Stars like the sun burn hydrogen in their core for most of their lives. Once the fuel runs out, they expand into red giants, growing hundreds of times larger and devouring nearby planets.
In the solar system, for example, this will include Mercury, Venus, and even Earth, all of which will be swallowed up by the red-hot sun about 5 billion years from now. Eventually, the sun loses its outer layer, leaving only a burned-out core, the white dwarf. Such stellar residues can still host planets, and many of these star systems are thought to exist in our galaxies.
Before, Schreiber and G? Yannsicke et al. have published papers detailing how enough high-energy photons were emitted to evaporate Jupiter, Saturn, Uranus and Neptune. As seen around WDJ0914 and 1914, some of the planet’s atmosphere’s gas will eventually fall on stars that turn into white dwarfs and will be observed by future extraterrestrial astronomers.
“Few astronomers think about the fate of planets orbiting dying stars. This discovery is strong evidence that the universe has challenged our minds again and again, taking us beyond established ideas. Nsicke said.