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Astronomers discover a strange diamond-shaped galaxy

The outer edge of the galactic disc is rotating at a speed in excess of 100,000 km/h. Suprime-Cam, Subaru Telescope

A team of Australian and European astronomers has discovered a highly unusual galaxy in the shape of an emerald-cut diamond roughly 70 million light years away.

The astronomers - from Australia, Germany, Switzerland and Finland - discovered the formation within a group of 250 galaxies.

“In the universe around us, most galaxies exist in one of three forms: spheroidal [a three-dimensional ellipse], disc-like, or lumpy and irregular in appearance,” said Associate Professor Alister Graham from Swinburne University of Technology.

The galaxy was a very unusual object, he said. “It’s one of those things that just makes you smile because it shouldn’t exist, or rather you don’t expect it to exist.

"It’s a little like the precarious Leaning Tower of Pisa or the discovery of some exotic new species which at first glance appears to defy the laws of nature.”

The discovery is published today in The Astrophysical Journal.

The galaxy was detected in a wide field-of-view image taken with the Japanese Subaru Telescope for an unrelated program by Swinburne astrophysicist Dr Lee Spitler.

The astronomers say the galaxy, known as LEDA 074886, resembles an inflated disc seen side on, like a short cylinder.

Images captured by the giant Keck Telescope in Hawaii have revealed that the outermost edge of this galactic disc is rotating at a speed in excess of 100,000 kilometres per hour.

“One possibility is that the galaxy may have formed out of the collision of two spiral galaxies,” said University of Swinburne Professor Duncan Forbes, co-author of the research.

“Sometimes advances in science are made by discovering an extreme example of something. We have found a galaxy that appears to be more rectangular in shape that any other galaxy. It is currently a mystery how such a rectangular galaxy could have formed. But we do know that the conditions must be fairly special as our galaxy is pretty rare.”

While the outer shape is reminiscent of galaxy mergers which don’t involve the production of new stars, the disc-like structure is comparable with mergers that do involve star formation.

One of the reasons the new galaxy was hard to find was because it was so small: it has 50 times fewer stars than the Milky Way galaxy, and it is located at a distance from us equivalent to 700 Milky Way galaxies placed end to end.

Michael Brown, a senior lecturer in astronomy at Monash Univeristy, said the galaxy was definitely an “odd ball”. “Perhaps [it is] the peculiar end-product of a merger of two galaxies.

"This may result from the different behaviour of stars and gas during galaxy mergers. The space between stars within galaxies is vast, so when two galaxies merge the individual stars rarely collide with each other. In contrast, clouds of gas within galaxies do collide during galaxy mergers.

"If this is a galaxy collision, what may have happened is the stars and gas have behaved differently. The stars have distributed themselves into the emerald cut shape, while the gas has settled down into a disk from which new stars are being formed.

"Odd balls” could be curios, he said, or they could challenge the way we thought about the universe.

Professor Graham added: “Curiously, if the orientation was just right, when our own disc-shaped galaxy collides with the disc-shaped Andromeda galaxy about three billion years from now we may find ourselves the inhabitants of a square looking galaxy.”

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