Heart Nebula

The Heart Nebula (also known as the Running Dog Nebula, Sharpless 2-190) is an emission nebula, 7,500 light-years (2,300 pc) away from Earth and located in the Perseus Arm of the Galaxy in the constellation Cassiopeia. It was discovered by William Herschel on 3 November 1787. In 1958, it was identified as a radio source by Gart Westerhout and is therefore also referred to as Westerhout 4 (or W4). It displays glowing ionized hydrogen gas and darker dust lanes. The brightest part of the nebula (a knot at its western edge) is separately classified as NGC 896, because it was the first part of the nebula to be discovered. The nebula's intense red output and its morphology are driven by the radiation emanating from a small group of hot stars near the nebula's center. This open cluster of stars, known as Collinder 26, Melotte 15, or IC 1805, contains a few bright stars nearly 50 times the mass of the Sun, and many more dim stars that are only a fraction of the Solar mass. The Heart Nebula is also made up of ionized oxygen and sulfur gasses, which are responsible for the rich blue and orange colors seen in narrowband images. The nebula also spans almost 2 degrees in the sky, covering an area four times that of the diameter of the full moon. The Heart Nebula belongs to a larger structure known as the W3/W4/W5 complex. It is also the brightest part of a superbubble known as the W4 superbubble , sometimes referred to as the W4 chimney, as it is believed that hot gas is transferred from the galactic disk to the halo through this structure.