typically depending on the mass of the original star. Various techniques based on the features of the supernova remnant estimate the Cygnus Loop progenitor star's mass at 12 to 15 Solar masses, a value that puts the expected remnant firmly within neutron star boundaries. However, despite many searches, no compact stellar remnant had been confidently identified since the identification of the supernova remnant. A noted anomaly is that in X-rays, the nebula appears perfectly spherical aside from a "blowout region" to the south. Searches for a compact stellar remnant have been largely concentrated here, as the hole may have been caused by the violent ejection of a neutron star. A detailed 2012 study of the blowout region identified a possible pulsar wind nebula, as well as a point-like source within it. Although at almost exactly the same position as a known Seyfert galaxy, the slight offset combined with a lack of a radio counterpart makes the point-like source probably unrelated to the galaxy. Whether the feature is a pulsar wind nebula, and if so whether it is related to the Cygnus Loop, is still unknown for certain. If it is indeed the compact stellar remnant of the supernova, the neutron star would have to have been ejected from the center of the nebula at a speed of roughly , depending on the precise age and distance of the remnant. Fiction In the novel Mindbridge by Joe Haldeman, the Cygnus Loop is the remains of the home star of an omnipotent, immortal race that ultimately decided to destroy itself. See also X-ray astronomy Radio astronomy Ultraviolet astronomy References External links Sharpless Catalog 103 Cygnus Loop image from NOAO, in one of the largest astronomical images yet made (universetoday.com). Cygnus Loop in ultraviolet light The loop at 1420 Mhz Source Supernova remnants X-ray astronomy Astronomical X-ray sources Cygnus (constellation) Sharpless objects