About 8,000 years ago, Neolithic humans would have witnessed what appeared to be a bright new star blazing in the northern sky. In fact, it was the violent explosion of a star 20 times the mass of our Sun. Now, the expanding remnant of that blast can be seen as the Cygnus Loop, a donut-shaped nebula that is approximately 6 times the apparent diameter of the full Moon.
This Hubble image shows a small section of the Veil Nebula. This section of the outer shell of the famous supernova remnant is in a region known as the Witch’s Broom Nebula (NGC 6960). Image credit: NASA / ESA / Hubble Heritage Team.
In 1997, Hubble’s Wide Field and Planetary Camera 2 (WFPC2) photographed a small portion of that remnant, called the Veil Nebula, providing detailed views of its structure.
Now, overlaying WFPC2 images with new Wide Field Camera 3 data provides even greater detail and allows astronomers to study how far the nebula has expanded since it was photographed almost two decades ago.
Deriving its name from its delicate, draped filamentary structures, the Veil Nebula is one of the best-known supernova remnants.
Also known as the Cirrus Nebula and the Filamentary Nebula, this object spans approximately 110 light-years and lies in the constellation Cygnus, about 2,100 light-years away.
Despite the nebula’s complexity and distance from us, the movement of some of its delicate structures is clearly visible – particularly the faint red hydrogen filaments. One such filament can be seen as it meanders through the middle of the brighter features.
Scientists suspect that before the Veil Nebula’s source star exploded it expelled a strong stellar wind. This wind blew a large cavity into the surrounding interstellar gas.
As the shock wave from the supernova expands outwards, it encounters the walls of this cavity – and forms the nebula’s distinctive structures.
Bright filaments are produced as the shock wave interacts with a relatively dense cavity wall, whilst fainter structures are generated by regions nearly devoid of material.
The object’s colorful appearance is generated by variations in the temperatures and densities of the chemical elements present.
Red corresponds to the glow of hydrogen; green from sulfur; and blue from oxygen.
The bluish features, outlining the cavity wall, appear smooth and arched in comparison to the fluffy green and red structures.
The red glow is from cooler gas that was excited by the shock collision at an earlier time and has subsequently diffused into a more chaotic structure.
Despite utilizing six full Hubble fields of view, new WFC3 images cover just a tiny fraction of the nebula’s outer limb. Located on the west side of the supernova remnant, this section of the outer shell is in a region known as NGC 6960.
