When stars use up their nuclear fuel, they turn into "white dwarf" stars. When white dwarf stars cool down, they crystallize.
In 2004, the Harvard-Smithsonian Center for Astrophysics discovered a cooled white dwarf 50 light years away from Earth.
At the core of that cooling star is a diamond 2,500 miles across, which weighs 5 million trillion trillion pounds, or around 2 thousand trillion trillion tons, or approximately 10 billion trillion trillion carats.
As the Harvard-Smithsonian Center explained:
Amazingly, according to the Harvard-Smithsonian team, our sun will also eventually become a giant diamond:A white dwarf is the hot core of a star, left over after the star uses up its nuclear fuel and dies. It is made mostly of carbon.
For more than four decades, astronomers have thought that the interiors of white dwarfs crystallized, but obtaining direct evidence became possible only recently.
"The hunt for the crystal core of this white dwarf has been like the search for the Lost Dutchman's Mine. It was thought to exist for decades, but only now has it been located," says co-author Michael Montgomery (University of Cambridge).
The white dwarf studied by Metcalfe, Montgomery, and Antonio Kanaan (UFSC Brazil), is not only radiant but also harmonious. It rings like a gigantic gong, undergoing constant pulsations.
"By measuring those pulsations, we were able to study the hidden interior of the white dwarf, just like seismograph measurements of earthquakes allow geologists to study the interior of the Earth. We figured out that the carbon interior of this white dwarf has solidified to form the galaxy's largest diamond," says Metcalfe.
Our Sun will become a white dwarf when it dies 5 billion years from now. Some two billion years after that, the Sun's ember core will crystallize as well, leaving a giant diamond in the center of our solar system.
"Our Sun will become a diamond that truly is forever," says Metcalfe.
High-resolution images and a Quicktime movie on the giant diamond discovery are here. See also this.
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