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The Cygnus Loop or Sharpless 103 is a large supernova remnant in the constellation Cygnus, an emission nebula measuring nearly 3° across. Some arcs of the loop, known collectively as the Veil Nebula or Cirrus Nebula, emit in the visible electromagnetic range. Radio, infrared, and X-ray images reveal the complete loop.
What is the Cygnus Loop?
Until recently the distance to the supernova remnant was estimated at about 2500 light-years. Recent studies, however, have shown that it must be closer. In 1999, William Blair, assuming that the shock wave should be expanding at the same rate in all directions, compared the angular expansion along the sides of the bubble (visible in Hubble Space Telescope images) with direct line-of-sight measurements of the radial expansion towards the Earth. He concluded that the actual size of the bubble was about 40% smaller than the conventional value, leading to a distance of about 1470 ly.
A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.
There are two common routes to a supernova: either a massive star may run out of fuel, ceasing to generate fusion energy in its core, and collapsing inward under the force of its own gravity to form a neutron staror a black hole; or a white dwarf star may accumulate (accrete) material from a companion star until it reaches a critical mass and undergoes a thermonuclear explosion.
Image: NASA / JPL-Caltech
Text: Wikipedia contributors. “Cygnus Loop.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 23 Jan. 2017. Web. 10 Aug. 2017. & Wikipedia contributors. “Supernova remnant.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 2 Apr. 2017. Web.10 Aug. 2017.