Supernova impostors are stellar explosions that appear at first to be a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

but do not destroy their progenitor stars. As such, they are a class of extra-powerful

nova A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramati ...

e. They are also known as Type V

supernovae A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when a ...

Eta Carinae Eta Carinae (η Carinae, abbreviated to η Car), formerly known as Eta Argus, is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around distant in t ...

analogs, and giant eruptions of

luminous blue variable Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of the Larg ...

s (LBV).

Appearance, origin and mass loss

Supernova impostors appear as remarkably faint supernovae of spectral type IIn—which have hydrogen in their spectrum and narrow spectral lines that indicate 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 This is a list of stars arranged by their absolute magnitude – their intrinsic stellar luminosity. This cannot be observed directly, so instead must be calculated from the apparent magnitude (the brightness as seen from Earth), the distance t ...

. The trigger mechanism of these outbursts remains unexplained, though it is thought to be caused by violating the classical

Eddington luminosity The Eddington luminosity, also referred to as the Eddington limit, is the maximum luminosity a body (such as a star) can achieve when there is balance between the force of radiation acting outward and the gravitational force acting inward. The sta ...

limit, initiating severe mass loss. If the ratio of radiated energy to kinetic energy is near unity, as in

, then we might expect an ejected mass of about 0.16 solar masses.

Examples

Possible examples of supernova impostors include the Great Eruption of

P Cygni P Cygni (34 Cygni) is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in ''Uranometria'' as a nova. Located about 5,300 light-years (1,560 parsecs) from Earth, it is a hypergian ...

SN 1961V SN 1961V was an abnormal, supernova-like event that was a potential supernova impostor. The potential impostor nature of SN 1961V was first identified by Fritz Zwicky in 1964. SN 1961V occurred in galaxy NGC 1058, about 9.3 Mpc away (about 3 ...

, SN 1954J, SN 1997bs, SN 2008S in

NGC 6946 NGC 6946, sometimes referred to as the Fireworks Galaxy, is a face-on intermediate spiral galaxy with a small bright nucleus, whose location in the sky straddles the boundary between the northern constellations of Cepheus and Cygnus. Its dista ...

, 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 UGC 4904 is a barred spiral galaxy in the constellation Lynx, located about 77 million light-years from Earth. On October 20, 2004, a supernova impostor was observed by Japanese amateur astronomer Koichi Itagaki within the galaxy. This same star ...

by Japanese amateur astronomer Koichi Itagaki. This LBV star exploded just two years later, on October 11, 2006, as supernova

SN 2006jc SN 2006jc was a supernova that was detected on October 9, 2006 in the galaxy UGC 4904, which is about 77 million light-years away in the constellation Lynx. It was first seen by Japanese amateur astronomer Koichi Itagaki, American amateur Tim Pu ...

References

{{star Variable stars Astronomical events

Appearance, origin and mass loss

Examples

See also

References