                APOD: 2017 December 28 - Recycling Cassiopeia A

                         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.

                               2017 December 28
                                      [2]
                            Recycling Cassiopeia A
                    Image Credit: NASA [3] , CXC, SAO [4]

Explanation: Massive stars in our Milky Way Galaxy live spectacular lives.
Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create
heavy elements in their cores. After a few million years, the enriched
material [5]  is blasted back into interstellar space where star formation can
begin anew. The expanding debris cloud known as Cassiopeia A is an example of
this final phase of the stellar life cycle. Light from the explosion which
created this supernova remnant would have been first seen in planet Earth's
sky [6]  about 350 years ago, although it took that light about 11,000 years
to reach us. This false-color Chandra X-ray Observatory image [7]  shows the
still hot filaments and knots in the Cassiopeia A remnant. High-energy
emission from specific elements has been color coded, silicon in red, sulfur
in yellow, calcium in green and iron in purple, to help astronomers explore
[8] the recycling of our galaxy's star stuff [9]  - Still expanding, the blast
wave is seen as the blue outer ring. The sharp X-ray image, spans about 30
light-years at the estimated distance of Cassiopeia A. The bright speck [10]
near the center is a neutron star, the incredibly dense, collapsed remains of
the massive stellar core.

                   Tomorrow's picture: more star stuff [11]

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Site notes:
  [1] archivepix.html
  [2] image/1712/casa_life.jpg
  [3] https://www.nasa.gov/
  [4] http://chandra.harvard.edu/
  [5] ap011026.html
  [6] http://spider.seds.org/spider/Vars/casA.html
  [7] http://chandra.harvard.edu/photo/2017/casa_life/
  [8] https://arxiv.org/abs/1111.7316
  [9] ap171119.html
  [10] ap170501.html
  [11] ap171229.html
  [12] ap171227.html
  [13] archivepix.html
  [14] lib/apsubmit2015.html
  [15] lib/aptree.html
  [16] http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [17] calendar/allyears.html
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  [19] lib/edlinks.html
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  [21] http://asterisk.apod.com/discuss_apod.php?date=171228
  [22] ap171229.html
  [23] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [24] http://www.phy.mtu.edu/
  [25] http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
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  [27] lib/about_apod.html#srapply
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