NGC 6960, the Veil Nebula

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  • Nebulosa del Velo

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Sometimes nature conspires to offer us a delicate and wonderful spectacle created from a disaster. The new image that the Agrupació Astronòmica d'Eivissa presents is a good example of this: NGC6960, also known as "The Witch's Broom," "The Finger of God," or "The Filamentous Nebula."

NGC6960 is located in the constellation of the Swan, at a distance of about 2100 light-years from us. It was discovered on September the 5th, 1784 by William Herschel and stands out for its curious and subtle filamentous structures. NGC6960 is one of the brightest parts of a gigantic remainder or remnant of a giant doughnut-shaped supernova called "The Swan's Loop" or "Veil Nebula", which presents an apparent size in the night sky of six full moons. Spreading over such a large area, its surface brightness is quite low, so the nebula is difficult to see even through an amateur telescope. The bright star of the image is 52 Cygni, visible to the naked eye from a dark place but unrelated to the old supernova remnant. Supernovae are created by the explosive, violent death of a massive star, and this one took place about 8000 years ago.

Astronomers suspect that, before the star that created the Veil Nebula exploded, it ejected a strong stellar wind. This wind formed an huge cavity in the surrounding interstellar gas. Later, as the shock wave of the supernova expanded outwards, it encountered the walls of this cavity and formed the delicate, distinctive filamentous structures of the nebula. The bright filaments were created when the shock wave interacted with a relatively dense cavity wall area, while the weaker structures were generated in regions almost devoid of material. The colorful appearance of the filaments is generated by variations in the temperatures and densities of the chemical elements present. In this case, blue denotes the presence of oxygen and red, atomic hydrogen. The red color occurs after the gas is swept by the shock wave - which moves at almost 1.5 million kilometers per hour - and the hydrogen inside the gas is excited by particle collisions right in the front of the shock wave.

In order to process this image, more than 350 high-resolution photographs taken by the AAE with the Telescope of Cala d'Hort, owned by the Consell d'Eivissa, have been needed, of which the processor, Faustino M. Márquez Pérez, member of the same AAE, selected a third of them. Individual frames were taken between June the 10th, 2015 and October the 30th, 2016 using four filters: Luminance, Red, Green and Blue.