Surprising Discovery of a Rare "Emerald-Cut" Galaxy

An international team of astronomers—from Australia, Germany, Switzerland, and Finland—has discovered a rare, rectangular-shaped galaxy (LEDA 074886) that has a striking resemblance to an emerald-cut diamond. While using the Subaru Prime Focus Camera (Suprime-Cam) to look for globular clusters of stars swarming around NGC 1407, a bright, giant galaxy in the Constellation Eridanus and 700 million light years from Earth, the researchers discovered an unusually shaped dwarf galaxy toward the edge of their image. Professor Alister Graham (Swinburne University of Technology, Australia), lead author of the paper describing the research, 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." Its discovery allows astronomers to obtain useful information for modeling other galaxies.

Figure: False-color image of LEDA 074886 taken with Subaru Telescope's Suprime-Cam. The central contrast has been adjusted to reveal the inner disk/bar-like component. Dr. Lee Spitler (Swinburne University of Technology, Australia) took this image.

Most galaxies in the universe around us exist in one of three forms: ellipsoidal, disk-like (usually in the shape of a flattened circular disk hosting a spiral pattern of stars), or irregular. Dwarf galaxies, probably the most common galaxies in the Universe, are small and have low intrinsic brightness (i.e., luminosity). One of the reasons that LEDA 074886 was hard to find is its dwarf-like status; it has 50 times less stars than our own Milky Way Galaxy, and its distance from Earth is equivalent to that spanned by 700 Milky Way galaxies placed end-to-end. The combined advantages of Subaru's large 8.2m primary mirror and its camera at prime focus gave the researchers such a wide field of view that they could observe objects beyond their intended targets and make the surprising discovery of the emerald-shaped dwarf galaxy. Additional information gleaned from the use of green, red, and infrared filters along with the good image quality seeing in the observation enabled the researchers to see and measure a stellar disk embedded within the rectangular-shaped galaxy. The blue color of the inner disk suggested a younger average age for this stellar population.

The astronomers suspect that the emerald-cut galaxy may resemble an inflated disk seen side-on, like a short cylinder. Research co-author Professor Duncan Forbes (Swinburne University of Technology, Australia) explained, "One possibility is that the galaxy may have formed out of the collision of two spiral galaxies. 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 disk that we have observed."

Despite its apparent uniqueness, partly due to its chance orientation, the team has gathered useful information for modeling other galaxies. While the outer rectangular shape is somewhat like galaxy simulations that don't involve the production of new stars, the disk-like structure is comparable with simulations involving star formation. "This highlights the importance of combining lessons learned from both types of past simulations, for better understanding of galaxy evolution," says Professor Graham. When our own disk-shaped Milky Way Galaxy collides with the disk-shaped Andromeda Galaxy in about three billion years from now, we may become inhabitants of a rectangular looking galaxy.

Reference:

The paper presenting the results of this research, "Leda 074886: A Remarkable Rectangular-Looking Galaxy", will appear in the Astrophysical Journal. It is tentatively scheduled for the May 1, 2012, Issue 750-1. Authors of the paper are:

Graham, A.W., Swinburne University of Technology, Australia
Spitler, L.R., Swinburne University of Technology, Australia
Forbes, D.A., Swinburne University of Technology, Australia
Lisker, T., Heidelberg University, Germany
Moore, B. University of Zurich, Switzerland
Janz, J., University of Oulu, Finland

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