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Large Binocular Telescope shows That Hercules Is Odd, Flat Dwarf Galaxy

17.09.2007
An international team of astronomers using the Large Binocular Telescope
(LBT) in Arizona has discovered that the Hercules Dwarf Galaxy is shaped like a cigar. That makes it an oddball among millions of its peers.

The Hercules Dwarf is a companion galaxy to our own Milky Way, but has only one ten-millionth as many stars. It was among several dwarf galaxies discovered earlier this year by the Sloan Digital Sky Survey.

Now astronomers using the LBT have discovered that this tiny galaxy, which is 430,000 light years away, is flat rather than round. Spiral galaxies, including our Milky Way, are flat because they rotate around their galactic centers. But dwarf galaxies don't rotate this way. They are more spherical.

The Hercules Dwarf Galaxy is the first flat dwarf galaxy astronomers have found among millions of well-studied dwarf galaxies.

"The Hercules Dwarf Galaxy is either unlike any of the millions of dwarf galaxies studied so far, or (else) it circles our Galaxy on an extremely plunging orbit," Matthew Coleman of the Max Planck Institute for Astronomy, Germany, said.

If the Hercules Dwarf revolves in some wildly eccentric orbit with the Milky Way, our big galaxy's gravity may have pulled Hercules' stars into a squashed, cigar-shaped disk when they were near the Milky Way's galactic core, Coleman said. The Milky Way has "tidally stretched" the Sagittarius Dwarf Galaxy this way. The Milky Way's gravity pulls more strongly on one side of Sagittarius than the other, stretching it out into a stream of stars. But Sagittarius is 10 times closer to the Milky Way's center than the Hercules Dwarf Galaxy is.

Whether Hercules was somehow tidally stretched in the past or if it's flat for some other as yet unknown reason, Coleman said, the Hercules Dwarf is "an exceptional, unparalleled object."

Coleman and his team will publish their results in the Astrophysical Journal Letters, http://xxx.lanl.gov/abs/0706.1669

LBT Director Richard Green called the result an exciting milestone: ³This is the first paper in the astronomical literature to be based on data from LBT, the very first official scientific result from a new state-of-the-art telescope.²

The Large Binocular Telescope Observatory is at 3,190 meters, or more than 10,000 feet, on Mount Graham in southeastern Arizona. The world's single largest optical/infrared telescope, the Large Binocular Telescope features two 8.4-meter mirrors on a single mount. The project's Italian partners have developed an optical "blue" camera now operating at prime focus on one of the mirrors, and they are completing another optical "red" camera soon to be installed at prime focus on the other mirror.

The astronomers used LBT's high-tech blue Large Binocular Camera to take new images of the Hercules Dwarf with 10 times more sensitivity than the Sloan Digital Sky Survey did. The Large Binocular Camera and telescope work together like a giant digital camera that takes images of ultra-faint objects with a field of view the size of the full moon.

The LBT team acquired all their published data on the Hercules Dwarf in relatively short exposure times for a total 80 minutes, University of Arizona astronomy Professor Jill Bechtold said. Much more sensitive observations are possible with the LBT, Bechtold noted. She is a co-author on the paper.

Emanuele Giallongo of INAF/Rome, who built the camera, said, "I am delighted to see that the new camera is delivering such exciting images to the astronomy community."

"We provided early 'science demonstration' time to our astronomers so that they could show what can be done with this new facility," Green said. "This result is just the first, with many more to come."

Combined light from the LBT's two giant mirrors is equivalent to an 11.8 meter, or approximately 39-foot, mirror. Combined light from the two mirrors and state-of-the-art adaptive optics will give the telescope the resolution of a 22.8-meter, or approximately 75-foot telescope.

Future high-tech instruments that will be used with the LBT include spectrographs of varying resolution and spectral sensitivity, and complex devices that will combine the light path of the two giant mirrors. U.S., German and Italian institutions are partners in the $120 million LBT Observatory. The University of Arizona in Tucson is a partner in the LBT Corp. on behalf of the Arizona university system.

The LBT is an international collaboration among institutions in the United States, Italy and Germany. The LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system, Istituto Nazionale di Astrofisica in Italy, the LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University, the Ohio State University, and the Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia.

Media Contact Information:
Klaus Jager Max Planck Institute for Astronomy + 49-62221 528 379 Matt Smith, LBT Corp. 520-321-1111

For more information and images for download, Visit the LBTO Web site, http://www.lbto.org

Download high-resolution image of the LBT on Mount Graham:
http://medusa.as.arizona.edu/lbto/image s/2006/12/061211a.j.JPG

Lori Stiles | University of Arizona
Further information:
http://uanews.org
http://xxx.lanl.gov/abs/0706.1669

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