Supernova impostor
Stellar explosions that mimic supernovae but leave their stars intact.
Supernova impostors are stellar outbursts that look like supernovae at first but leave their parent stars intact, placing them in the category of unusually powerful novae. They go by several other names: Type V supernovae, Eta Carinae analogs, and giant eruptions of luminous blue variables (LBVs).
These events appear as unusually dim supernovae of spectral type IIn, meaning their light shows hydrogen and narrow spectral lines indicating slow-moving gas. The impostors brighten by several magnitudes compared to their pre-eruption state, reaching peak absolute visual magnitudes between −11 and −14—as luminous as the brightest known stars. What triggers these eruptions is still unknown, though the leading idea is that the star exceeds the classical Eddington luminosity limit, triggering extreme mass loss. If the ratio of radiated to kinetic energy is close to one—as seen in Eta Carinae—the ejected mass would be roughly 0.16 solar masses.
Possible examples include the Great Eruption of Eta Carinae, P Cygni, SN 1961V, SN 1954J, SN 1997bs, SN 2008S, and SN 2010dn, where surviving progenitor stars have been detected. One notable impostor was spotted on October 20, 2004, in the galaxy UGC 4904 by Japanese amateur astronomer Kōichi Itagaki. That LBV star later exploded as supernova SN 2006jc on October 11, 2006.
- Peak absolute visual magnitude
- -11 to -14
- Ejected mass estimate
- 0.16 solar masses (if radiated-to-kinetic energy ratio near unity, as in Eta Carinae)
- Spectral type
- IIn (hydrogen present, narrow spectral lines indicating low gas speeds)
- Brightness relative to pre outburst
- exceed pre-outburst states by several magnitudes
Lore & Background
Supernova impostors appear as remarkably faint supernovae of spectral type IIn, which have hydrogen in their spectrum and narrow spectral lines indicating relatively low gas speeds. These impostors exceed their pre-outburst states by several magnitudes, with typical peak absolute visual magnitudes of −11 to −14, making these outbursts as bright as the most luminous stars. The trigger mechanism of these outbursts remains unexplained, though it is thought to be caused by violating the classical Eddington luminosity limit, initiating severe mass loss. If the ratio of radiated energy to kinetic energy is near unity, as in Eta Carinae, then we might expect an ejected mass of about 0.16 solar masses.
Possible examples of supernova impostors include the Great Eruption of Eta Carinae, P Cygni, SN 1961V, SN 1954J, SN 1997bs, SN 2008S, and SN 2010dn where detections of the surviving progenitor stars are claimed. One supernova impostor that made news after the fact was the one observed on October 20, 2004, in the galaxy UGC 4904 by Japanese amateur astronomer Kōichi Itagaki. This LBV star exploded just two years later, on October 11, 2006, as supernova SN 2006jc.
Reader's Guide
Supernova impostors are significant because they challenge the traditional understanding of stellar death, as they mimic supernovae without destroying their progenitor stars. Their classification as extra-powerful novae and their alternative names—Type V supernovae, Eta Carinae analogs, and giant eruptions of luminous blue variables—highlight their unique position in stellar astrophysics. The article notes that their trigger mechanism remains unexplained, though it is thought to involve violating the classical Eddington luminosity limit, leading to severe mass loss. The estimated ejected mass of about 0.16 solar masses, based on the Eta Carinae example, provides a quantitative link to observed outbursts. The legacy of these objects includes their role in identifying surviving progenitor stars after outbursts, as claimed for examples like SN 2008S and SN 2010dn. The case of the impostor observed in UGC 4904 in 2004, which later produced supernova SN 2006jc, underscores the connection between these impostors and genuine supernovae, suggesting that some impostors may be precursors to final stellar explosions.
More in Variable Stars 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced