The heavy metals miniplanet survived the death of its star

This is what will happen when our sun dies:

First, the hydrogen-powered nuclear reactor in its center will run out of fuel. The sun will become a red giant, swelling 100 times bigger and swallowing Mercury, Venus and maybe even our own planet, with all life as we know it. Then, the helium contained in its core will be transformed into carbon, until it lacks the materials and the energy necessary to continue. Finally, it convulses and collapses, losing its outer layers until there remains only a dense and glowing sphere not much larger than the Earth – a white dwarf.

Nobody can tell what our solar system will look like after this cataclysm, about 5 billion years into the future. But a new planetary system could offer a clue.

In the pale glow of a white dwarf at 410 light-years from Earth, the heavy metal core of a body, which may have already been a planet, drifts into the ruins of its former being .

The strange and broken world, described Thursday in the journal Science, is the second body found in orbit around this type of dead star. Scientists have stated that this is the proof of what was happening to planetary bodies when their suns went out – a fate that awaits most of the solar systems in the universe, including ours.

"We have this glimpse of our possible future," said Jessie Christiansen, an astronomer from the NASA's Exoplanets Scientific Institute who did not participate in the new study. "It's exciting" – although slightly terrifying – "and you can imagine it happening here."

The host star of the recently discovered planet fragment is a white dwarf, known as SDSS J122859.93 + 104032.9. (To save time and save your breath, scientists who study it simply call it "1228".)

Christopher Manser, an astrophysicist at the University of Warwick, Great Britain, was first drawn in 1228 several years ago, as it seemed like a disc of debris swirled around him. Using the largest optical telescope in the world, the Gran Telescopio Canarias in Spain, he sought to split the light signature of the debris disc into component parts, which would tell him what he was doing.

He was surprised to see regular disturbances of the disc – a gas stream similar to that of a comet's tail. A year of observation showed that gas appeared every two hours, as if on wheels. Such a regular signal could only be produced by a "planetary" or planetary fragment, rotating around the star, and throwing gas in some way.

The two-hour orbital period of the new world is so short that it must be incredibly close to the white dwarf; if you put it in our solar system, it would be in the sun's atmosphere.

He must also be incredibly resistant. A white dwarf packs the mass of almost all the sun into a sphere representing 1% of the size of the sun. These objects exert an enormous gravitational pull that could easily tear a planet apart.

"This body must have enough density or internal force to survive this intense gravity," Manser said. "The densest thing we could think of was iron."

In our solar system, there is a world like this: the all-metal asteroid 16 Psyche. Scientists believe that this strange body was once the iron heart of a larger planet whose rocky crust and molten mantle had been removed.

The planetesimal may have the same story: born as a rocky world, further back in the solar system, it was pushed towards the white dwarf by a transient disturbance. In the claws of the enormous gravity of the dead star, the fragile crust and mantle disintegrated, leaving behind the hard metal core.

The observations of the white dwarf debris disk reinforce this notion. It's full of calcium, oxygen and magnesium – "the building blocks of rocky bodies," said Manser.

But there are still questions about this strange little world. Manser and his colleagues do not know exactly what is causing the gaseous disturbances in the debris disk of 1228. Gases may evaporate from the planetary surface. Another hypothesis suggests that the presence of the iron world causes collisions in the debris disk generating gas.

Meanwhile, scientists hope to spot more planetary systems like this. Many white dwarves show signs of "pollution" by rocky materials and at least six of them appear to be surrounded by debris disks.

"All of this suggests that nearly half of the white dwarfs have a planetary system that has survived their evolutions and is springing up in the material," Manser said.

Lisa Kaltenegger, astrophysicist, director of the Carl Sagan Institute at Cornell University, pointed out that the majority of stars in the universe are doomed to become white dwarves after their deaths. (Only stars much larger than the sun are big enough to explode in supernova and eventually form a black hole.)

Kaltenegger, who did not participate in the latest study, published last year an analysis in the Astrophysical Journal Letters suggesting that planets in the right orbit surrounding a white dwarf could potentially be habitable for billions of years.

This latest discovery "is the first puzzle that there may be planets around white dwarves for a while," she said.

"Whether or not you can consider a second genesis (of life) around these remaining stellar nuclei," she added, "it is still beautiful to consider."