Mystery in the Perseus Cluster   
       
   July 24, 2014:  The Universe is a big place, full of unknowns.  Astronomers   
   using NASA's Chandra X-ray Observatory have just catalogued a new one.   
       
   "I couldn't believe my eyes," says Esra Bulbul of the Harvard Center for   
   Astrophysics.  "What we found, at first glance, could not be explained by   
   known physics."   
       
   https://www.youtube.com/watch?v=3439YtdQZ1Y   
       
   A new ScienceCast video explores the mystery signal coming from the heart of   
   the Perseus Cluster.  Play it   
       
   Together with a team of more than a half-dozen colleagues, Bulbul has been   
   using Chandra to explore the Perseus Cluster, a swarm of galaxies   
   approximately 250 million light years from Earth.   Imagine a cloud of gas in   
   which each atom is a whole galaxy-that's a bit what the Perseus cluster is   
   like.  It is one of the most massive known objects in the Universe.   
       
   The cluster itself is immersed in an enormous 'atmosphere' of superheated   
   plasma-and it is there that the mystery resides.   
       
   Bulbul explains:  "The cluster's atmosphere is full of ions such as Fe XXV, Si   
   XIV, and S XV.  Each one produces a 'bump' or 'line' in the x-ray spectrum,   
   which we can map using Chandra. These spectral lines are at well-known x-ray   
   energies."   
       
   Yet, in 2012 when Bulbul added together 17 day's worth of Chandra data, a new   
   line popped up where no line should be.   
       
   "A line appeared at 3.56 keV (kilo-electron volts) which does not correspond   
   to any known atomic transition," she says.  "It was a great surprise."   
       
   At first, Bulbul herself did not believe it. "It took a long time to convince   
   myself that this line is neither a detector artifact, nor a known atomic   
   line," she says. "I have done very careful checks.  I have re-analyzed the   
   data; split the data set into different sub groups; and checked the data from   
   four other detectors on board two different observatories. None of these   
   efforts made the line disappear."   
       
   http://chandra.si.edu/index.html   
       
   For more results from NASA's flagship X-ray observatory, visit the Chandra   
   Home PageIn short, it appears to be real.  The reality of the line was further   
   confirmed when Bulbul's team found the same spectral signature in X-ray   
   emissions from 73 other galaxy clusters.  Those data were gathered by Europe's   
   XMM-Newton, a completely independent X-ray telescope.   
       
   Moreover, about a week after Bulbul team posted their paper online, a   
   different group led by Alexey Boyarsky of Leiden University in the Netherlands   
   reported evidence for the same spectral line in XMM-Newton observations of the   
   Andromeda galaxy.  They also confirmed the line in the outskirts of the   
   Perseus cluster.   
       
   The spectral line appears not to come from any known type of matter, which   
   shifts suspicion to the unknown: dark matter.   
       
   "After we submitted the paper, theoreticians came up with about 60 different   
   dark matter types which could explain this line. Some particle physicists have   
   jokingly called this particle a 'bulbulon'," she laughs.   
       
   The menagerie of dark matter candidates that might produce this kind of line   
   include axions, sterile neutrinos, and "moduli dark matter" that may result   
   from the curling up of extra dimensions in string theory.   
       
   Solving the mystery could require a whole new observatory.  In 2015, the   
   Japanese space agency is planning to launch an advanced X-ray telescope called   
   "Astro-H." It has a new type of X-ray detector, developed collaboratively by   
   NASA and University of Wisconsin scientists, which will be able to measure the   
   mystery line with more precision than currently possible.     
   "Maybe then," says Bulbul, "we'll get to the bottom of this."   
       
   Credits:   
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)