                        Astronomy Picture of the Day

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      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2021 August 22

                   Explosions from White Dwarf Star RS Oph
           Illustration Credit & Copyright: David A. Hardy & PPARC

   Explanation: Spectacular explosions keep occurring in the binary star
   system named RS Ophiuchi. Every 20 years or so, the red giant star
   dumps enough hydrogen gas onto its companion white dwarf star to set
   off a brilliant thermonuclear explosion on the white dwarf's surface.
   At about 5,000 light years distant, the resulting nova explosions cause
   the RS Oph system to brighten up by a huge factor and become visible to
   the unaided eye. The red giant star is depicted on the right of the
   above drawing, while the white dwarf is at the center of the bright
   accretion disk on the left. As the stars orbit each other, a stream of
   gas moves from the giant star to the white dwarf. Astronomers speculate
   that at some time in the next 100,000 years, enough matter will have
   accumulated on the white dwarf to push it over the Chandrasekhar Limit,
   causing a much more powerful and final explosion known as a supernova.
   Starting early this month, RS Oph was again seen exploding in a bright
   nova.

                   Tomorrow's picture: one galaxy tripled
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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