Astronomers have discovered a huge, icy planet that is evaporating as it orbits the super-high-temperature debris of a sun-like star. According to the researchers, this is the first time evidence has been observed of an extraterrestrial gas giant orbiting the star. The discovery provides a rare window for astronomers to study the fate of the solar system for billions of years to come.
Yellow dwarfs, such as the sun, combine hydrogen atoms at their core to form helium atoms through a process called thermonuclear fusion, producing a lot of energy. In about 5 billion years, our sun will deplete its hydrogen supply and begin to fuse helium atoms. By then, the sun will be transformed from a yellow dwarf star into a red giant, which will be 2,000 times brighter than it is now, and will be so large that it can devour Mercury, Venus and Earth. Eventually, the sun will shed its outer layer, leaving behind a small, dying nuclear residue, the white dwarf.
Now, astronomers have found the first circumstantial evidence of a gas-like giant planet that survived the star’s chaotic red-star phase, which is currently orbiting a white dwarf. An international team responsible for the study analyzed 7,000 white dwarfs that are part of the Sloan Digital Sky Survey. They found that the light traces of a star – WDJ0914 and 1914 – contained trace chemical elements that had never been associated with a white dwarf before.
To reveal the mystery of WDJ0914 and 1914, astronomers turned to the European Southern Observatory’s VlT in the Atacama Desert. VLT turned its attention to the strange white dwarf star and created a detailed spectrum or decomposition of the starlight with a powerful spectrometer called X-shooter. By analyzing the spectrum and searching for black bars called “absorption lines,” scientists were able to determine what chemicals were present inside or around the star.
Subsequent observations confirmed the presence of hydrogen, oxygen and sulfur embedded in the WDJ0914 and 1914 starlight. According to the new paper, unexpected matter is not part of the star itself, but is located in a gas disk that hovers like a white dwarf.
The amount of gas detected in the spectrum was found to be similar to the amount found in the atmospheres of large cold planets such as Neptune and Uranus. If such a planet orbits a white dwarf, the intense ultraviolet rays that the white dwarf pours out will slowly evaporate its atmosphere. This will explain the presence of a gas disk.
The researchers then combined their data with a theoretical model to find out what was happening around WDJ0914 and 1914. According to their experiments, icy planets may be at least twice the size of small stars. The icy giant planet is just 10 million kilometers (6 million miles) from the superheated surface of the white dwarf and has completed its full orbit in just 10 days. It is estimated that about 3,000 tons of destroyed planetary material fall into the white dwarf every second.
Such a planet orbits a star so close to earth that it raises questions in itself. The gas giant could not have been created in that orbit and remained there only because its parent star would be destroyed when it expanded outwards during the red giant.
Instead, the authors of the new study believe the planet may have formed further afield, pushing it inward by the gravitational pull of another object once WDJ0914 and 1914 shrink into a white dwarf. The theory suggests that at least one other planet must survive the dramatic evolution of its star and lurk on the periphery that modern telescopes cannot detect. The observations of WDJ0914 and 1914 provide a window for astronomers to study the fate of the solar system.
The study was published in the journal Nature.