Hello All!   
      
   600 Mysteries in the Night Sky    
      
   Oct 18, 2011: NASA's Fermi team recently released the second catalog of   
   gamma-ray sources detected by their satellite's Large Area Telescope (LAT). Of   
   the 1873 sources found, nearly 600 are complete mysteries. No one knows what   
   they are.    
      
   "Fermi sees gamma rays coming from directions in the sky where there are no   
   obvious objects likely to produce gamma rays," says David Thompson, Fermi   
   Deputy Project Scientist from Goddard Space Flight Center.    
      
   http://www.nasa.gov/images/content/585379main_2-year-all-sky_GT1_GeV_labels.jpg   
      
   An all-sky map of gamma-ray emissions made by the Fermi Space Telescope.   
   Hundreds of the sources in the map are complete mysteries. [larger image]    
   Gamma rays are by their very nature heralds of great energy and violence. They   
   are a super-energetic form of light produced by sources such as black holes   
   and massive exploding stars. Gamma-rays are so energetic that ordinary lenses   
   and mirrors do not work. As a result, gamma-ray telescopes can't always get a   
   sharp enough focus to determine exactly where the sources are.    
      
   For two thirds of the new catalog's sources the Fermi scientists can, with at   
   least reasonable certainty, locate a known gamma ray-producing object*, such   
   as a pulsar or blazar, in the vicinity the gamma-rays are coming from. But the   
   remaining third - the "mystery sources" -- have the researchers stumped, at   
   least for now. And they are the most tantalizing.    
      
   http://www.youtube.com/watch?v=EQHuF3BGZzw   
      
   Nearly 600 sources in the latest Fermi catalog are unidentified. "Some of the   
   mystery sources could be clouds of dark matter - something that's never been   
   seen before," speculates Thompson.    
      
   About 85% of the gravitational mass of the universe is dark matter. The stuff   
   we see makes up the rest. Dark matter is something that pulls on things with   
   the force of its gravity but can't be detected in any other way. It doesn't   
   shine - doesn't emit or scatter light - hence the adjective "dark."    
      
   Astronomers cannot detect dark matter directly using optical or radio   
   telescopes. But dark matter just might shine in gamma rays.    
      
   "We've been using Fermi to search for dark matter for a long time," says the   
   principal investigator for the Large Area Telescope, Peter Michelson of   
   Stanford University.    
      
   Some researchers believe that when two dark matter antiparticles bump into   
   each other, they will annihilate, producing gamma rays. Concentrated clouds of   
   dark matter could form a gamma ray source at specific wavelengths detectable   
   by Fermi.    
      
   "If we see a bump in the gamma-ray spectrum -- a narrow spectral line at high   
   energies corresponding to the energy of the annihilating particles - we could   
   be the first to 'apprehend' dark matter," says Michelson.    
      
   The team plans to continue observing the mystery sources. Fermi scans the   
   entire sky ever three hours, and this ongoing sequence of observations "piles   
   up" gamma rays for the researchers to analyze. So far, too few gamma rays have   
   been collected from the mystery sources to form definite conclusions.    
      
   http://www.youtube.com/watch?v=EQHuF3BGZzw   
      
   Colliding galaxy clusters are one possible explanation for the mystery   
   sources. Another, less-dark possibility for some of the mystery sources is   
   colliding galaxy clusters. According to Michelson and Thompson, clashes of   
   such magnitude would generate super large scale shock waves that would   
   accelerate particles. Others of the sources, they say, might be some brand new   
   phenomenon, perhaps something involving galactic black holes.    
      
   When all is said and done, many of the mystery sources could prove to be   
   familiar. "[They] will probably turn out to be members of known source classes   
   - things we know but haven't recognized yet, like undiscovered pulsars, binary   
   systems, and supernova remnants," says Michelson.    
      
   "Of course we're hoping for something really exotic like dark matter, but we   
   have to look first at all the other options," says Thompson. "Fermi is an   
   ongoing mission. We'll continue to search for answers to these puzzles and   
   perhaps turn up even more surprises."    
      
   Will notorious dark matter finally be nabbed? Stay tuned!    
      
      
   Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA   
      
   More Information    
   Fermi Gamma-ray Space Telescope -- home page    
      
   Footnote: *Among the known classes in the second Fermi LAT catalog are almost   
   100 gamma-ray pulsars -- super dense neutron stars that are blinking in gamma   
   rays. They are 1 « times the mass of our sun, but crushed to the size of a   
   city."Pulsars rotate rapidly and the light from them sweeps past us like light   
   from a light house," explains Thompson. "Some of them rotate as fast as a   
   kitchen blender -- hundreds of times per second!" The LAT team has rock- solid   
   identification on 83 pulsars in our own galaxy. But the largest single class   
   of gamma-ray sources the LAT "sees" is blazars from active galactic nuclei.   
   Blazars make up over 1000 of the 1873 sources. "They are of course   
   extra-galactic," says Michelson. "Only about 25 of these are rock solid   
   identifications, but we believe the others, because of their location, are   
   likely associated with active galactic nuclei blazars too." Active galactic   
   nuclei are the cores of galaxies. "The gamma rays are probably coming from the   
   vicinity of black holes, which have 1 million to 1 billion times the mass of   
   our sun," says Thompson. "A black hole pulls everything into itself by virtue   
   of its unbelievable strong gravity. As it does so, enormous energy is released   
   and squirted away from the black hole as a beam of particles and radiation   
   moving at nearly the speed of light. It's called a blazar if the jet is aimed   
   at us and we are looking down the barrel. But the jet of energy doesn't come   
   out of the black hole itself; rather it is powered by material falling into   
   the black hole." Binary systems constitute another known source class in the   
   new catalog. They are made up of a neutron star or black hole orbiting a large   
   normal star.    
      
   Credits: NASA's Fermi Gamma-Ray Space Telescope mission is an astrophysics and   
   particle physics partnership, developed in collaboration with the U.S.   
   Department of Energy, along with important contributions from academic   
   institutions and partners in France, Germany, Italy, Japan, Sweden, and the   
   United States. The mission's main instrument, the Large Area Telescope (LAT),   
   is making pioneering observations of gamma-ray bursts at higher energies than   
   ever before from space. Another instrument onboard, the Fermi Gamma-Ray Burst   
   Monitor, is monitoring gamma-ray bursts at lower energies. The combination of   
   the GBM and the LAT provides a powerful tool for studying GRBs over a very   
   wide range of energies. The GBM is a collaboration among scientists at the   
   Marshall Space Flight Center, the University of Alabama in Huntsville, the Max   
   Planck Institute for Extraterrestrial Physics in Germany, and the Los Alamos   
   National Laboratory.    
       
      
   Regards,   
      
   Roger    
   --- timEd/386 1.10.y2k+   
    * Origin: NCS BBS - Houma, LA - (1:3828/7)