It's the compressed heart of an old star that was once bright like our Sun but has since faded and shrunk.
Astronomers have decided to call the star "Lucy" after the Beatles song, Lucy in the Sky with Diamonds.
"You would need a jeweller's loupe the size of the Sun to grade this diamond," says astronomer Travis Metcalfe, of the Harvard-Smithsonian Center for Astrophysics, who led the team of researchers that discovered it.
The diamond star completely outclasses the largest diamond on Earth,
the 546-carat Golden Jubilee which was cut from a stone brought out
of the Premier mine in South Africa.
The huge cosmic diamond - technically known as BPM 37093 - is actually
a crystallised white dwarf. 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
For more than four decades, astronomers have thought that the
interiors of white dwarfs crystallised, but obtaining direct evidence
became possible only recently.
The white dwarf is not only radiant but also 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.
Astronomers expect 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 crystallise as well, leaving a giant diamond in the
centre of the solar system.
"Our Sun will become a diamond that truly is forever," says Metcalfe.