Astronomers discover ‘emerald-cut’ galaxy
March 23, 2012
Kamuela HI—An international team of astronomers has discovered and explained a rare square galaxy with a striking resemblance to an emerald cut diamond by using both Keck and Subaru telescopes. The astronomers - from Australia, Germany, Switzerland and Finland - discovered the rectangular-shaped galaxy within a group of 250 galaxies some 70 million light years away.
“In the Universe around us, most galaxies exist in one of three forms: spheroidal, disc-like, or lumpy and irregular in appearance,” said astrophysicist Alister Graham from Swinburne University of Technology in Sydney, Australia. Gravity tends to form stars and galaxies into round shapes, like balls or discs. A rectangular-shaped galaxy is unusual.
“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,” said Graham. “It’s a little like the…discovery of some exotic new species which at first glance appears to defy the laws of nature.”
The unusually shaped galaxy was detected in a wide field-of-view image taken with the Japanese Subaru Telescope for an unrelated program by Swinburne astrophysicist Lee Spitler. The astronomers suspect it is unlikely that this galaxy is shaped like a cube. Instead, they believe that it may resemble an inflated disc seen side on, like a short cylinder.
Support for this scenario comes from observations with Keck Observatory’s Echellette Spectrograph and Imager (ESI), which revealed a rapidly spinning, thin disc with a side-on orientation lurking at the centre of the galaxy. The outermost measured edge of this galactic disc is rotating at a speed in excess of 100,000 kilometers per hour.
“One possibility is that the galaxy may have formed out of the collision of two spiral galaxies,” said Swinburne’s Duncan Forbes, a co-author of the research. “While the pre-existing stars from the initial galaxies were strewn to large orbits creating the emerald-cut shape, the gas sank to the mid-plane where it condensed to form new stars and the disc that we have observed.”
Despite its apparent uniqueness, partly due to its chance orientation, the astronomers have managed to glean useful information for modelling other galaxies. While the outer boxy shape is somewhat reminiscent of galaxy merger simulations which don’t involve the production of new stars, the disc-like structure is comparable with merger simulations involving star formation.
“This highlights the importance of combining lessons learned from both types of past simulation for better understanding galaxy evolution in the future,” said Graham.
“One of the reasons this emerald cut galaxy was hard to find is due to its dwarf-like status: it has 50 times less stars than our own Milky Way galaxy, plus its distance from us is equivalent to that spanned by 700 Milky Way galaxies placed end-to-end. 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.”
The results will be published in The Astrophysical Journal.
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The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Big Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system which cancels out much of the interference caused by Earth’s turbulent atmosphere. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.