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N6946-BH1 is a disappearing supergiant star and failed supernova candidate formerly seen in the galaxy NGC 6946, on the northern border of the constellation of Cygnus.The star, either a red supergiant [1] or a yellow hypergiant, [3] was 25 times the mass of the Sun, and was 20 million light years distant from Earth.
Theoretically, a red supergiant star may be too massive to explode into a supernova, and collapse directly into being a black hole, without the bright flash. They would however generate a burst of gravitational waves. This process would occur in the higher mass red supergiants, explaining the absence of observed supernovae with such progenitors.
Supergiants typically have surface gravities of around log(g) 2.0 cgs and lower, although bright giants (luminosity class II) have statistically very similar surface gravities to normal Ib supergiants. [20] Cool luminous supergiants have lower surface gravities, with the most luminous (and unstable) stars having log(g) around zero. [9]
By the end of their lives red supergiants may have lost a substantial fraction of their initial mass. The more massive supergiants lose mass much more rapidly and all red supergiants appear to reach a similar mass of the order of 10 M ☉ by the time their cores collapse. The exact value depends on the initial chemical makeup of the star and ...
For Type II supernovae, the collapse is eventually halted by short-range repulsive neutron-neutron interactions, mediated by the strong force, as well as by degeneracy pressure of neutrons, at a density comparable to that of an atomic nucleus. When the collapse stops, the infalling matter rebounds, producing a shock wave that propagates outward ...
It was the first supernova that modern astronomers were able to study in great detail, and its observations have provided much insight into core-collapse supernovae. SN 1987A provided the first opportunity to confirm by direct observation the radioactive source of the energy for visible light emissions, by detecting predicted gamma-ray line ...
More recently, at the 2013 Huntsville Gamma-ray Burst Symposium, several scientists proposed that GRB 101225A, along with GRB 111209A and 121027A are part of a new class of gamma ray bursts, termed ultra-long bursts and caused by the collapse of low metallicity blue supergiant stars.
Betelgeuse is a red supergiant that has evolved from an O-type main-sequence star. After core hydrogen exhaustion, Betelgeuse evolved into a blue supergiant before evolving into its current red supergiant form. [98] Its core will eventually collapse, producing a supernova explosion and leaving behind a compact remnant. The details depend on the ...