White dwarf star
An artist's impression of debris around a white dwarf starNasa, ESA, STScI, and G. Bacon (STScI)

Scientists have solved the riddle of celestial archaeology with a new theory explaining how collapsed stars become polluted, which points to the ominous fate awaiting our planet.

Researchers from the University of Leicester and the University of Arizona have investigated white dwarf stars, the super-dense remains of Sun-like stars that ran out of fuel and collapsed to the size of Earth.

According to Space.com, the "dim stellar corpses" are the "last observable stage of evolution for low-and-medium-mass stars". It has been established that many hot white dwarf atmospheres, essentially of pure hydrogen or pure helium, are contaminated by other elements, such as carbon, silicon and iron.

Yet the origin of these elements, known in astronomical terms as metals, has remained a decade-old mystery.

Professor Martin Barstow, from University of Leicester and president of the Royal Astronomical Society who led the research, sheds more light on the phenomenon. He said: "The precise origin of the metals has remained a mystery and extreme differences in their abundance between stars could not be explained. It was believed that this material was 'levitated' by the intense radiation from deeper layers in the star."

The latest research have discovered that many of the stars show signs of contamination by rocky material, which are the left-overs from a planetary system.

Barstow added: "We found that in stars with polluted atmospheres, the ratio of silicon to carbon matched that seen in rocky material, much higher than found in stars or interstellar gas."

The researchers surveyed 89 white dwarfs, using the Far Ultraviolet Spectroscopic Explorer to obtain their spectra (dispersing the light by colour). Within these, the "fingerprints" of carbon, silicon, phosphorous and sulphur can be seen, when these elements are present in the atmosphere.

The study also points to the ultimate fate of the Earth billions of years from now, predicted to end up as a contamination within the white dwarf Sun.

Barstow explained: "The new work indicates that at around one-third of all hot white dwarfs are contaminated in this way, with the debris most likely in the form of rocky minor planet analogues."

"This implies that a similar proportion of stars like our Sun, as well as stars that are a little more massive like Vega and Fomalhaut, build systems containing terrestrial planets. This work is a form of celestial archaeology where we are studying the 'ruins' of rocky planets and/or their building blocks, following the demise of the main star."

According to Barlow, the mystery of this composition is a problem scientists have been trying to solve for over two decades. He concluded: "It is exciting to realise that they are swallowing up the leftovers from planetary systems, perhaps like our own, with the prospect that more detailed follow-up work will be able to tell us about the composition of rocky planets orbiting other stars."

Their research is featured in MNRAS- the Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.