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Archive for December 19, 2011

Cassini Significant Events 12/7/11 – 12/13/11

December 19, 2011 Leave a comment

The most recent spacecraft telemetry was acquired on Dec. 13 from the Deep Space Network tracking complex at Canberra, Australia. The Cassini spacecraft is in an excellent state of health and with the exception of the CAPS instrument being powered off, all subsystems are operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the “Present Position” page at: http://saturn.jpl.nasa.gov/mission/presentposition/.

Full Story: http://saturn.jpl.nasa.gov/news/significantevents/significantevents20111215/

Physicist And Former Astronaut John Grunsfeld To Head NASA Science Directorate

December 19, 2011 Leave a comment

NASA has named physicist and former astronaut John Grunsfeld as the new associate administrator for the Science Mission Directorate at the agency’s headquarters in Washington. Grunsfeld will take the reins of the office effective Jan. 4, 2012. He succeeds Ed Weiler, who retired from NASA on Sept. 30.

Grunsfeld currently serves as the deputy director of the Space Telescope Science Institute in Baltimore, which manages the science program for the Hubble Space Telescope and is a partner in the forthcoming James Webb Space Telescope. His background includes research in high energy astrophysics, cosmic ray physics and in the emerging field of exoplanet studies with specific interest in future astronomical instrumentation.

A veteran of five space shuttle flights, Grunsfeld visited Hubble three times as an astronaut, performing a total of eight spacewalks to service and upgrade the observatory.

Full Story: http://www.nasa.gov/home/hqnews/2011/dec/HQ_11-396_Grunsfeld.html

Ultra-Compact Dwarf Galaxies Are Bright Star Clusters

December 19, 2011 Leave a comment

Astronomy & Astrophysics is publishing a new statistical study of the so-called ‘ultra-compact dwarf galaxies’ (UCDs), which are still mysterious objects. A team of astronomers has investigated how many of these UCDs exist in nearby galaxy clusters and groups. They show that the properties of UCDs match those of bright star clusters.

Astronomy & Astrophysics is publishing the results of a detailed investigation of how many ‘ultra-compact dwarf galaxies’ (UCDs) can be found in nearby galaxy clusters. UCDs were recognized as a populous and potentially distinct class of stellar systems about a decade ago. But they are still mysterious objects that are characterized by a compact morphology (30-300 light-years in size) and high masses (more than one million solar masses). More generally, their properties (e.g., their size, shape, or luminosity) are similar to those of both star clusters and dwarf galaxies. Several hundred UCDs have been found to date. Two main formation channels for these puzzling objects have been proposed so far. UCDs might either be very massive star clusters or be ‘normal’ dwarf galaxies transformed by tidal effects.

S. Mieske, M. Hilker, and I. Misgeld (ESO) present a statistical study of the UCD population: they define new statistical tools that relate the number of UCDs to the total luminosity of their host environment. This allows them to use statistical arguments to test the hypothesis that UCDs are bright star clusters. They predict that if UCDs are bright star clusters, we would expect to find only one or two UCDs around the Milky Way, which corresponds to what is seen, as omega Centauri is the only Milky Way satellite that can be considered a UCD.

Full Story: http://www.aanda.org/index.php?option=com_content&task=view&id=788&Itemid=277&lang=en_GB.utf8%2C+en_GB.UT

New Insight into the Milky Way’s Central Bar

December 19, 2011 Leave a comment

It sounds like the start of a bad joke: do you know about the bar in the center of the Milky Way Galaxy? Astronomers first recognized almost 80 years ago that the Milky Way Galaxy, around which the sun and its planets orbit, is a huge spiral galaxy. This isn’t obvious when you look at the band of starlight across the sky, because we are inside the galaxy: it’s as if the sun and solar system is a bug on the spoke of a bicycle wheel. But in recent decades astronomers have suspected that the center of our galaxy has an elongated stellar structure, or bar, that is hidden by dust and gas from easy view. Many spiral galaxies in the universe are known to exhibit such a bar through the center bulge, while other spiral galaxies are simple spirals. And astronomers ask, why? In a recent paper Dr. Andrea Kunder, of Cerro Tololo Inter-American Observatory (CTIO) in northern Chile, and a team of colleagues have presented data that demonstrates how this bar is rotating.

As part of a larger study dubbed BRAVA, for Bulge Radial Velocity Assay, a team assembled by Dr. R. Michael Rich at UCLA, measured the velocity of a large sample of old, red stars towards the galactic center. (See image) They did this by observing the spectra of these stars, called M giants, which allows the velocity of the star along our line of sight to be determined. Over a period of 4 years almost 10,000 spectra were acquired with the CTIO Blanco 4-meter telescope, located in the Chilean Atacama desert, resulting in the largest homogeneous sample of radial velocities with which to study the core of the Milky Way. Analyzing the stellar motions confirms that the bulge in the center of our galaxy appears to consist of a massive bar, with one end pointed almost in the direction of the sun, which is rotating like a solid object. Although our galaxy rotates much like a pinwheel, with the stars in the arms of the galaxy orbiting the center, the BRAVA study found that the rotation of the inner bar is cylindrical, like a toilet roll holder. This result is a large step forward in explaining the formation of the complicated central region of the Milky Way.

Full Story: http://www.noao.edu/news/2011/pr1109.php