A failed supernova is an astronomical event in time domain astronomy in which a star suddenly brightens as in the early stage of a supernova, but then does not increase to the massive flux of a supernova. They could be counted as a subcategory of supernova imposters. They have sometimes misleadingly been called unnovae.[1]
Failed supernovae are thought to create stellar black holes by the collapsing of a red supergiant star in the early stages of a supernova. When the star can no longer support itself, the core collapses completely, forming a stellar-mass black hole, and consuming the nascent supernova without having the massive explosion. For a distant observer, the red supergiant star will seem to wink out of existence with little or no flare-up. The observed instances of these disappearances seem to involve supergiant stars with masses above 17 solar masses.
Failed supernovae are one of several events that theoretically signal the advent of a black hole born from an extremely massive star, others including hypernovae and long-duration gamma-ray bursts.
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.[2] [3]
| Event | Date | Location | Notes | |
|---|---|---|---|---|
| NGC3021-CANDIDATE-1 | Disappearance of a 25-30 MSun F8 supergiant observed in archival HST data | [4] | ||
| N6946-BH1 | March 2009 | Disappearance of an 18-25 MSun red supergiant | [5] [6] | |