The first evidence of a giant planet orbiting a dead white dwarf star has found in the form of a disc of gas formed from its evaporating atmosphere. Researchers found the hidden giant planet revealed around a small white dwarf star.
The Neptune-like planet orbits a star a quarter of its size about once every ten days, leaving a comet-like tail of gas comprised of hydrogen, oxygen, and sulfur in its wake.
It is the first evidence of a giant planet orbiting a white dwarf star and suggests that there could be many more planets around such stars waiting to discover.
The star WDJ0914+1914 identified in a survey of ten thousand white dwarfs observed by the Sloan Digital Sky Survey. Scientists at Warwick analyzed subtle variations in the light emitted from the system to identify the elements present around the star.
They detected very minute spikes of hydrogen in the data, which was unusual in itself, but also of oxygen and sulfur, which they had never seen before.
Using the Very Large Telescope of the European Southern Observatory in Chile to more observations of this star, they found that the shape of the hydrogen, oxygen, and sulfur features are typical indicators of a ring of gas.
But, the observations show that it is a single white dwarf with a disc around it roughly ten times the size of our sun, made of hydrogen, oxygen, and sulfur. Such a system has never seen before, and it was immediately clear to me that this was a unique star.
When the astronomers averaged all the spectra they obtained over two nights in Chile it was clear that WDJ0914+1914 was accreting sulfur and oxygen from the disc. Analyzing the data, they were able to measure the composition of the disc and concluded that it matches what scientists expect for the deeper layers of our own solar system’s ice giants, Uranus and Neptune.
The researcher showed through a set of calculations that the 28,000 degrees Celsius hot white dwarf is evaporating this hidden icy giant by bombarding it with high energy photons and pulling its lost mass into a gas disc around the star at a rate of over 3,000 tons per second.
This star has a planet that we can’t see, but because the star is so hot it is evaporating the planet, and we detect the atmosphere it is losing.
There could be many cooler white dwarfs that have planets but lacking the high-energy photons necessary to drive evaporation, so we wouldn’t be able to find them with the same method. But, some of those planets might detectable using the transit method once the Large Synoptic Survey Telescope goes on the sky.
This discovery is major progress because over the past two decades we had growing evidence that planetary systems survive into the white dwarf stage.
We’ve seen a lot of asteroids, comets and other small planetary objects hitting white dwarfs, and explaining these events require larger, planet-mass bodies further out. Having evidence for an actual planet that itself scattered in is an important step.
The white dwarf we see today was once a star like a sun but ran out of fuel, swelled up into a red giant, a few 100 times the size of the sun.
During that phase of its life, the star will have lost about half of its mass and what left has shrunk ending up the size of the Earth the white dwarf is the burnt-out core of the former star.
, today’s orbit of the planet around the white dwarf would have been deep inside the red giant, so scattering with some other planets in the system, a kind of cosmic pool game moved it close to the white dwarf after the red giant’s outer layers lost.
Once our sun runs out of fuel in about 4.5 billion years it will shed its outer layers, destroying Mercury, Venus, and the Earth, and expose the burnt-out core the white dwarf.
The astronomers argue that this planetary evaporation and later accretion by young white dwarfs is a common process and that it might open a new window towards studying the chemical composition of the atmospheres of extrasolar gas giant planets.
We stunned when we realized that when observing hot white dwarfs, we are seeing signatures from extrasolar planet atmospheres.
While this hypothesis needs further confirmation, it might indeed open the doors towards understanding extrasolar planet atmospheres.