Why is the Hercules Dwarf Galaxy so flat?
First accepted refereed publication based on observations
with the new Large Binocular Telescope
Through some of the very first scientific observations with the brand-new Large Binocular Telescope
(LBT) in Arizona, an international team of astronomers has found that a recently discovered tiny companion
galaxy to our Milky Way, named the Hercules Dwarf Galaxy, has truly exceptional properties: while basically
all of its known peers in the realm of these tiny dwarf galaxies are rather round, this galaxy at a distance
of 430000 Light Years appears highly flattened, either the shape of a disk or of a cigar.
The stars in many large galaxies are arranged in a disk-like configuration, as in our own Milky Way. Yet in smaller galaxies like the Hercules Dwarf, which despite its name has only a 10-millionth as many stars as the Milky Way, a disk-like configuration has never been observed before. Among the millions of well-studied galaxies none was ever identified to have a cigar-like shape.
An explanation for the galaxy’s unusual shape is that it is being disrupted by the gravitational forces of the Milky Way. This effect is definitely seen in another of the Milky Way's satellites, the Sagittarius Dwarf. Yet, this object is 10 times closer to the Milky Way’s center than the Hercules Dwarf Galaxy, and hence much more affected by the destructive “tidal forces” of our Galaxy. The Hercules Dwarf Galaxy can only have experienced a similar fate if its orbit would have brought it exceptionally close to the inner parts of the Milky Way. So, “The Hercules Dwarf Galaxy is either unlike any of the millions of galaxies studied so far, or circles our Galaxy on an extremely plunging orbit: an exceptional, unparalleled object at any rate”, says Matthew Coleman of the Max Planck Institute for Astronomy in Germany, who headed this study.
These inferences were enabled by the very deep images provided by the brand-new Large Binocular Telescope (LBT), the largest single telescope in the world, which is located on the 3190-meter high Mount Graham in Arizona. Two giant mirrors with a diameter of 8.4 meters each, are hosted on the same mount acting as gigantic field glasses.
The pictures of the Hercules Dwarf Galaxy were created using the high-tech Large Binocular Camera (LBC-Blue), mounted at the Prime Focus of one of the two 8.4-meter mirrors. LBC-Blue and its future twin for the red spectral range, LBC-red, are being developed by Italian partners in the project. The camera and telescope work together like a giant digital camera which is able to capture images of ultra-faint objects with a field of view the size of the full moon. “I am delighted to see that the new camera is delivering such exciting images to the Astronomy community, off the bat,” says Emanuele Giallongo of INAF/Rome, who built the Camera. “We provided early ‘science demonstration time’ to our Astronomers," says Richard Green, LBT Director, “so that they could show what can be done with this new facility. This result is just the first, with many more to come.”
By combining the optical paths of the two individual mirrors, the LBT will collect in its final increment as much light as a telescope whose mirrors have a diameter of 11.8 meters. This is a factor of 24 larger than the 2.4-meter mirror of the Hubble Space Telescope. Even more importantly, the LBT will then have the resolution of a 22.8-meter telescope, because it will use the most modern adaptive optics, superimposing pictures with an interferometric procedure. The astronomers are thus able to compensate for the blurring caused by air turbulence. With that power, the LBT will open completely new possibilities in researching planets outside the solar system and the investigation of the faintest and most distant galaxies.
The LBC camera is the first of a suite of high-tech instruments with which the LBT will be equipped in the future. These additional instruments include spectrographs with different resolution and spectral sensitivity as well as very complex instruments which will combine the light path of the two giant main mirrors. Both the telescope and instruments are being built by 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 Leibniz Institute for Astrophysics 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.
Due to the impressive first pictures and results, the astronomers now are very confident that the $120 million project is on the way to open a new door for spectacular observations of planets, stars and galaxies.
The complete author list is:
Matthew G. Coleman
(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany)
Jelte T. A. de Jong (Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany)
Nicolas F. Martin (Max-Planck-Institut für Astronomie, Königstuhl 17,D-69117 Heidelberg, Germany)
Hans-Walter Rix (Max-Planck-Institut für Astronomie, Königstuhl 17,D-69117 Heidelberg, Germany)
David J. Sand (Chandra Fellow, Steward Observatory, The University of Arizona, Tucson, AZ 85721)
Eric F. Bell (Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany)
Richard W. Pogge (Dep. of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210-1173)
David J. Thompson (Large Binocular Telescope Observatory, Univ. of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721-0065)
H. Hippelein (Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany)
E. Giallongo (INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy)
R. Ragazzoni (INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy)
Andrea DiPaola (INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy)
Jacopo Farinato (INAF, Osservatorio Astronomico di Padova, vicolo dell'Osservatorio, 5, 35122 Padova, Italy)
Riccardo Smareglia (INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo, 11, 34131 Trieste, Italy)
Vincenzo Testa (INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy)
Jill Bechtold (Steward Observatory, The University of Arizona, Tucson, AZ 85721)
John M. Hill (Large Binocular Telescope Observatory, Univ. of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721-0065)
Peter M. Garnavich (Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge MA 02138)
Richard F. Green (Large Binocular Telescope Observatory, Univ. of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721-0065)
Editor's Note – Further information can be found at http://www.lbto.org
A high resolution picture of the LBT can be found at
Coleman and his team will publish their results in the Astrophysical Journal Letters,
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