     APOD: 2018 January 2 - Unexpected X Rays from Perseus Galaxy Cluster

                         Astronomy Picture of the Day

    Discover the cosmos! [1] Each day a different image or photograph of our
 fascinating universe is featured, along with a brief explanation written by a
                           professional astronomer.

                                2018 January 2
                                      [2]
                Unexpected X-Rays from Perseus Galaxy Cluster
   Image Credit: X-ray:  NASA/CXO/Oxford University/J. Conlon et al.; Radio:
       NRAO/AUI/NSF/Univ. of Montreal/Gendron-Marsolais et al.; Optical:
                      NASA/ESA/IoA/A. Fabian et al.; DSS

Explanation: Why does the Perseus galaxy cluster shine so strangely in one
specific color of X-rays? No one is sure, but a much-debated hypothesis holds
that these X-rays [3] are a clue to the long-sought identity of dark matter
[4] . At the center of this mystery is a 3.5 Kilo- [5] electronvolt [6] (KeV)
X-ray color that appears to glow excessively only when regions well outside
the cluster [7]  center are observed, whereas the area directly surrounding a
likely central supermassive black hole [8]  is actually deficient in 3.5 KeV
X-rays. One proposed resolution [9] -- quite controversial -- is that
something never seen before might be present: florescent [10]  dark matter
(FDM). This form of particle dark matter [11]  might be able to absorb 3.5 KeV
X-radiation. If operating, FDM [12] , after absorption, might later emit these
X-rays from all over the cluster, creating an emission line [13] . However,
when seen superposed [14]  in front of the central region surrounding the
black hole [15] , FDM's absorption would be more prominent, creating an
absorption line [16] . Pictured [17] , a composite image of the Perseus galaxy
cluster [18]  shows visible and radio light in red, and X-ray light [19]  from
the Earth-orbiting Chandra Observatory [20]  in blue.

         Free APOD Lectures: January 5 in NYC & January 9 in DC [21]
                    Tomorrow's picture: helical space [22]

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    Authors & editors: Robert Nemiroff [34] (MTU [35] ) & Jerry Bonnell [36]
                                  (UMCP [37] )
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Site notes:
  [1] archivepix.html
  [2] image/1801/PerseusCluster_DSSChandra_3600.jpg
  [3] https://science.nasa.gov/ems/11_xrays
  [4] http://chandra.harvard.edu/xray_astro/dark_matter/
  [5] https://en.wikipedia.org/wiki/Kilo-
  [6] https://en.wikipedia.org/wiki/Electronvolt
  [7] http://chandra.harvard.edu/photo/2017/dark/dark_BU.mp4
  [8] ap171022.html
  [9] https://arxiv.org/abs/1608.01684
  [10] https://en.wikipedia.org/wiki/Fluorescence
  [11] https://home.cern/about/physics/dark-matter
  [12] https://www.youtube.com/watch?v=1m7g-DEyTUE
  [13] http://astronomy.swin.edu.au/cosmos/E/Emission+Line
  [14]
http://cdn.earthporm.com/wp-content/uploads/2015/03/
cute-cats-sleeping-on-dogs-22__605.jpg
  [15] ap170327.html
  [16] https://en.wikipedia.org/wiki/Spectral_line
  [17] http://chandra.harvard.edu/photo/2017/dark/
  [18] ap110712.html
  [19] ap170504.html
  [20] http://chandra.harvard.edu/about/
  [21] http://asterisk.apod.com/viewtopic.php?f=28&t=37750
  [22] ap180103.html
  [23] ap180101.html
  [24] archivepix.html
  [25] lib/apsubmit2015.html
  [26] lib/aptree.html
  [27] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [28] calendar/allyears.html
  [29] /apod.rss
  [30] lib/edlinks.html
  [31] lib/about_apod.html
  [32] http://asterisk.apod.com/discuss_apod.php?date=180102
  [33] ap180103.html
  [34] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [35] http://www.phy.mtu.edu/
  [36] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [37] http://www.astro.umd.edu/
  [38] lib/about_apod.html#srapply
  [39] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [40] https://astrophysics.gsfc.nasa.gov/
  [41] https://www.nasa.gov/
  [42] https://www.nasa.gov/centers/goddard/
  [43] http://www.mtu.edu/
