Australasian Science: Australia's authority on science since 1938

Diamonds in the Sky

By David Reneke

David Reneke brings news from the space and astronomy communities around the world.

The galaxy’s largest diamond has been found, but you’d better carry a deep wallet because this 10 billion trillion trillion carat monster has a cost that’s literally astronomical.

“You would need a jeweller’s magnifying glass the size of the Sun to grade this diamond!” says astronomer Travis Metcalfe from the Harvard Smithsonian Centre for Astrophysics, who leads a team of researchers that discovered the giant gem.

The newly discovered cosmic diamond is a chunk of crystallised carbon. It’s the burned out corpse of a star named BPM 37093, 50 light years from the Earth in the constellation Centaurus 500 trillion km away.

After it was discovered, astronomers nicknamed the space diamond “Lucy” after the Beatles song Lucy in the Sky with Diamonds. It’s around 4000 km across and weighs 5 million trillion trillion imperial pounds, which translates to approximately 10 billion trillion trillion carats.

This is the mother of all diamonds. It completely outclasses the largest diamond on Earth, the 530 carat Star of Africa, which resides in the Crown Jewels of England.

The huge cosmic gem is actually the crystallised carbon remnant of a white dwarf star, the hot core left over after the star uses up its nuclear fuel and dies. It’s composed mostly of carbon and oxygen created by the past thermonuclear fusion of helium nuclei.

Astronomers say that our Sun will become a white dwarf when it dies five billion years from now. Its core will crystallise as well, leaving a giant diamond like this one in the centre of our solar system.

How do we know this? Astronomers had suspected since the 1960s that the interiors of white dwarfs would be crystallised, and Lucy seems to confirm that.

The Most Distant Object Ever Seen
Astronomers have pushed NASA’s Hubble Space Telescope to it limits by finding what they believe to be the most distant object ever seen in the universe. It’s a compact galaxy made of blue stars that existed only 480 million years after the Big Bang, and it’s tiny. You could quite comfortably fit 100 of these mini-galaxies inside our Milky Way.

Lying at a distance of 13.2 billion light years – some 3% of the age of the universe – places this object roughly 150 million light years more distant than the previous record holder. The observations provide the best insights yet into the birth of the first stars and galaxies and the evolution of the universe.

Previous searches had found dozens of slightly older galaxies, telling astronomers that the rate of star birth increased quickly just after the universe was born. “It’s an astonishing increase in such a short period, happening in just 1% of the age of the universe,” said Ivo Labbe of the Carnegie Observatories and co-author of the study.

Astronomers don’t know exactly when the first stars appeared in the universe, but every step back in time takes them deeper into the early universe’s formative years when stars and galaxies were just beginning to emerge in the aftermath of the Big Bang.

Astronomers know that if they go back another couple of hundred million years, toward the Big Bang, they’ll see absolutely dramatic things happening but they’ll require the infrared vision of NASA’s James Webb Space Telescope, the successor to Hubble.

Astronomers plumb the depths of the universe by measuring how much the light from an object has been stretched by the expansion of space. The protogalaxy is only visible at the farthest infrared wavelengths observable by Hubble. This means that the expansion of the universe has stretched its light farther than any other galaxy previously identified. In fact, to the very limit of Hubble’s capabilities!

The object appears as a faint dot of starlight in the Hubble exposures. It is too young and too small to have the familiar spiral shape that is characteristic of galaxies in the local universe, such as the Milky Way.

Astronomers eagerly await the new space and ground-based telescopes due to be commissioned in this and the following decades to find out more.