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.
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.
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.
09h 50m 55.39s +33° 33′ 14.5″
|Disappearance of a 25-30 MSun F8 supergiant observed in archival HST data|||
|N6946-BH1||March 2009||NGC 6946
20h 35m 27.56s +60° 08′ 08.2″
|Disappearance of an 18-25 MSun red supergiant|||
Stellar explosion can refer to
type Ia supernova
Type Ib and Ic supernovae
Type II supernova
Supernova impostor, stellar explosions that appear similar to supernova, but do not destroy their progenitor stars
Luminous red nova, an explosion thought to be caused by stellar collision
solar flares are a minor type of stellar explosion
Tidal disruption event, the pulling apart of a star by tidal forcesN6946-BH1
N6946-BH1 is a disappearing red supergiant star in another galaxy, NGC 6946, on the northern border of the constellation of Cygnus. The star was 25 times the mass of the sun, and was 20 million light years distant from Earth. In March through to May 2009 its bolometric luminosity increased to at least a million solar luminosities, but by 2015 it had disappeared from optical view. In the mid and near infrared an object is still visible, however, it is fading away with a brightness proportional to t−4/3. The brightening was insufficient to be a supernova, and is called a failed supernova.The star's coordinates were at RA 20h 35m 27.56s and Dec +60° 08′ 08.29″. The brightness of the star, given by its apparent magnitude in different colour bands on 2 July 2005 is given by R = 21, V = 21, B = 22, U = 23. Prior to the optical outburst the star was about 100,000 times as bright as the sun. After the outburst it was invisible in the visual band and has declined to 5000 times as bright as the sun in infrared radiation.
One hypothesis is that the core of the star collapsed to form a black hole. The collapsing matter formed a burst of neutrinos that lowered the total mass of the star by a fraction of a percent. This caused a shock wave that blasted out the star's envelope to make it brighter. After the idea that a black holes are usually formed after a supernova, N6946-BH1 has given evidence that, instead of following this process, the star may automatically collapse into a black hole.Observed type II supernovae do not originate from stars with initial masses greater than about 18 M☉, and the rate of large star formation appears to exceed the rate of supernovae. The expectation is that something else is happening to these extra large stars. Failed supernovae and black hole formation is one proposed explanation. If this event indeed reflected the formation of a black hole, it is the first time that black hole formation has been observed.Stellar black hole
A stellar black hole (or stellar-mass black hole) is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. The process is observed as a hypernova explosion or as a gamma ray burst. These black holes are also referred to as collapsars.Supernova
A supernova ( plural: supernovae or supernovas, abbreviations: SN and SNe) is a transient astronomical event that occurs during the last stellar evolutionary stages of the life of a massive star, whose dramatic and catastrophic destruction is marked by one final, titanic explosion. This causes the sudden appearance of a "new" bright star, before slowly fading from sight over several weeks or months or years.
Supernovae are more energetic than novae. In Latin, nova means "new", referring astronomically to what appears to be a temporary new bright star. Adding the prefix "super-" distinguishes supernovae from ordinary novae, which are far less luminous. The word supernova was coined by Walter Baade and Fritz Zwicky in 1931.
Only three Milky Way, naked-eye supernova events have been observed during the last thousand years, though many have been observed in other galaxies. The most recent directly observed supernova in the Milky Way was Kepler's Supernova in 1604, but the remnants of recent supernovae have also been found. Observations of supernovae in other galaxies suggest they occur on average about three times every century in the Milky Way, and that any galactic supernova would almost certainly be observable with modern astronomical telescopes.
Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical mechanics have been established and accepted by most astronomers for some time.
Supernovae can expel several solar masses of material at speeds up to several percent of the speed of light. This drives an expanding and fast-moving shock wave into the surrounding interstellar medium, sweeping up an expanding shell of gas and dust observed as a supernova remnant. Supernovae are a major source of elements in the interstellar medium from oxygen through to rubidium. The expanding shock waves of supernova can trigger the formation of new stars. Supernova remnants might be a major source of cosmic rays. Supernovae might produce strong gravitational waves, though, thus far, the gravitational waves detected have been from the merger of black holes and neutron stars.UGC 12682
UGC 12682 is an irregular galaxy, located in the constellation of Pegasus.
In November 2008, 14-year-old amateur astronomer Caroline Moore from New York became the youngest supernova discoverer when she found SN 2008ha in UGC 12682.