Uk Hidden giant planet discovered orbiting tiny white dwarf star

James Marshall
December 5, 2019

Now, astronomers have discovered what they believe to be the first indirect evidence of a massive planet that has survived its star's chaotic red giant phase, and is currently orbiting a white dwarf.

"It took a few weeks of very hard thinking to figure out that the only way to make such a disk is the evaporation of a giant planet", said Matthias Schreiber, an astronomer at the University of Valparaiso in Chile, who was vital to determining the past and future evolution of the freakish system.

These findings had been printed Wednesday within the journal Nature. The team had inspected around 7000 white dwarfs observed by the Sloan Digital Sky Survey and found one to be unlike any other.

Astronomers at Warwick analysed subtle variations in the light emitted from the system to identify the elements present around the star.

So, the team trained the European Southern Observatory's Very Large Telescope (VLT) in Chile on WDJ0914+1914. "However, our observations show that it is a single white dwarf with a disk around it roughly 10 times the size of our sun, made exclusively of hydrogen, oxygen, and sulfur". These behemoths go supernova when they die, and their remnants generally end up as neutron stars or black holes, objects even denser and more exotic than white dwarfs.

"We were stunned when we realized that when observing hot white dwarfs, we are potentially seeing signatures from extrasolar planet atmospheres", Schreiber says. This icy giant travels at a distance of just 10 million km (6 million miles) from the super-hot surface of the white dwarf, and completes a full orbit in just 10 days.

The Neptune-like planet is thought to be more than four times the size of the Earth-sized white dwarf. When these stars finish burning their nuclear fuel, they'll first bloat up as enormous red giants, then eventually collapse down into white dwarfs, which pack about one solar mass into a sphere the size of Earth. "Such a system has never been seen before, and it was immediately clear to me that this was a unique star". According to their experiments, the icy planet is likely to be at least twice as large as the tiny star. Most of the gas escapes, but some is pulled into a disc swirling into the star at a rate of 3000 tonnes per second. This disc is what gives away the presence of the otherwise hidden Neptune-like planet.

"But somehow this newly-discovered planet has survived".

Stars like our Sun burn hydrogen in their cores for most of their lives.

"Eventually, the Sun will become a white dwarf and still have Mars, the asteroid belt and Jupiter orbiting it".

The good news here is that there may be a way to see our sun reach its white dwarf phase, as long as it can survive a few billion years and can relocate and survive on Jupiter or Saturn. It suggests that evaporating planets around dead stars may be somewhat common throughout the universe.

The revelation is the first of its kind as, before now, no other planet had been found to have lived through a star's transition to a white dwarf. In about six billion years, the Sun, a medium-size yellow star, will have puffed up to about two hundred times its current size.

While the astronomers could not directly observe the planet, the extreme heat of the 28,000 C star is causing it to slowly evaporate.

"Until recently, very few astronomers paused to ponder the fate of planets orbiting dying stars".

He added that having evidence for an actual planet was an "important step".

"At first, we thought that this was a binary star with an accretion disc formed from mass flowing between the two stars", says lead author Boris Gaensicke, a professor of the physics department at University of Warwick. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become "the world's biggest eye on the sky".

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