A supernova is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.
SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately 51.4 kiloparsecs from Earth and was the closest observed supernova since Kepler's Supernova. 1987A's light reached Earth on February 23, 1987, and as the earliest supernova discovered that year, was labeled "1987A". Its brightness peaked in May, with an apparent magnitude of about 3.
A super-luminous supernova is a type of stellar explosion with a luminosity 10 or more times higher than that of standard supernovae. Like supernovae, SLSNe seem to be produced by several mechanisms, which is readily revealed by their light-curves and spectra. There are multiple models for what conditions may produce an SLSN, including core collapse in particularly massive stars, millisecond magnetars, interaction with circumstellar material, or pair-instability supernovae.
Messier 61 is an intermediate barred spiral galaxy in the Virgo Cluster of galaxies. It was first discovered by Barnaba Oriani on May 5, 1779, six days before Charles Messier discovered the same galaxy. Messier had observed it on the same night as Oriani but had mistaken it for a comet. Its distance has been estimated to be 45.61 million light years from the Milky Way Galaxy. It is a member of the M61 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.
SN 1885A was a supernova in the Andromeda Galaxy, the only one seen in that galaxy so far by astronomers. It was the first supernova ever seen outside the Milky Way, though it was not appreciated at the time how far away it was. It is also known as "Supernova 1885".
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 distance from Earth is about 25.2 million light-years or 7.72 megaparsecs, similar to the distance of M101 in the constellation Ursa Major. Both were once considered to be part of the Local Group, but are now known to be among the dozen bright spiral galaxies near the Milky Way but beyond the confines of the Local Group. NGC 6946 lies within the Virgo Supercluster.
SN 2005df was a Type Ia supernova in the barred spiral galaxy NGC 1559, which is located in the southern constellation of Reticulum. The event was discovered in Australia by Robert Evans on the early morning of August 5, 2005 with a 13.8 magnitude, and was confirmed by A. Gilmore on August 6. The supernova was classified as Type Ia by M. Salvo and associates. It was positioned at an offset of 15.0″ east and 40.0″ north of the galaxy's nucleus, reaching a maximum brightness of 12.3 on August 18. The supernova luminosity appeared unreddened by dust from its host galaxy.
SN 2005cs was a supernova in the spiral galaxy M51, known as the Whirlpool Galaxy. It was a type II-P core-collapse supernova, discovered June 28, 2005 by Wolfgang Kloehr, a German amateur astronomer. The event was positioned at an offset of 15″ west and 78″ south of the galactic nucleus of M51. Based on the data, the explosion was inferred to occur 2.8 days before discovery. It was considered under-luminous for a supernova of its type, releasing an estimated 3×1050 erg in energy.
A Type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.
SN 1994D was a Type Ia supernova event in the outskirts of galaxy NGC 4526. It was offset by 9.0″ west and 7.8″ south of the galaxy center and positioned near a prominent dust lane. It was caused by the explosion of a white dwarf star composed of carbon and oxygen. This event was discovered on March 7, 1994 by R. R. Treffers and associates using the automated 30-inch telescope at Leuschner Observatory. It reached peak visual brightness two weeks later on March 22. Modelling of the light curve indicates the explosion would have been visible around March 3-4. A possible detection of helium in the spectrum was made by W. P. S. Meikle and associates in 1996. A mass of 0.014 to 0.03 M☉ in helium would be needed to produce this feature.
A Type II supernova or SNII results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun (M☉) to undergo this type of explosion. Type II supernovae are distinguished from other types of supernovae by the presence of hydrogen in their spectra. They are usually observed in the spiral arms of galaxies and in H II regions, but not in elliptical galaxies; those are generally composed of older, low-mass stars, with few of the young, very massive stars necessary to cause a supernova.
SN 2006gy was an extremely energetic supernova, also referred to as a hypernova or quark-nova, that was discovered on September 18, 2006. It was first observed by Robert Quimby and P. Mondol, and then studied by several teams of astronomers using facilities that included the Chandra, Lick, and Keck Observatories. In May 2007 NASA and several of the astronomers announced the first detailed analyses of the supernova, describing it as the "brightest stellar explosion ever recorded". In October 2007 Quimby announced that SN 2005ap had broken SN 2006gy's record as the brightest-ever recorded supernova, and several subsequent discoveries are brighter still. Time magazine listed the discovery of SN 2006gy as third in its Top 10 Scientific Discoveries for 2007.
SN 1993J is a supernova observed in the galaxy M81. It was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was the second-brightest type II supernova observed in the twentieth century behind SN 1987A, peaking at a visible apparent magnitude of 10.7 on March 30, with a second peak of 10.86 on April 18.
SN 2014J was a type-Ia supernova in Messier 82 discovered in mid-January 2014. It was the closest type-Ia supernova discovered for 42 years, and no subsequent supernova has been closer as of 2023. The supernova was discovered by chance during an undergraduate teaching session at the University of London Observatory. It peaked on 31 January 2014, reaching an apparent magnitude of 10.5. SN 2014J was the subject of an intense observing campaign by professional astronomers and was bright enough to be seen by amateur astronomers.
A hypernova is a very energetic supernova thought to result from an extreme core-collapse scenario. In this case, a massive star collapses to form a rotating black hole emitting twin astrophysical jets and surrounded by an accretion disk. It is a type of stellar explosion that ejects material with an unusually high kinetic energy, an order of magnitude higher than most supernovae, with a luminosity at least 10 times greater. They usually appear similar to a type Ic supernova, but with unusually broad spectral lines indicating an extremely high expansion velocity. Hypernovae are one of the mechanisms for producing long gamma ray bursts (GRBs), which range from 2 seconds to over a minute in duration. They have also been referred to as superluminous supernovae, though that classification also includes other types of extremely luminous stellar explosions that have different origins.
NGC 4424 is a spiral galaxy located in the equatorial constellation of Virgo. It was discovered February 27, 1865 by German astronomer Heinrich Louis d'Arrest. This galaxy is located at a distance of 13.5 million light years and is receding with a heliocentric radial velocity of 442 km/s. It has a morphological class of SB(s)a, which normally indicates a spiral galaxy with a barred structure (SB), no inner ring feature (s), and tightly-wound spiral arms (a). The galactic plane is inclined at an angle of 62° to the line of sight from the Earth. It is a likely member of the Virgo Cluster of galaxies.
iPTF14hls is an unusual supernova star that erupted continuously for about 1,000 days beginning in September 2014 before becoming a remnant nebula. It had previously erupted in 1954. None of the theories nor proposed hypotheses fully explain all the aspects of the object.
NGC 1325 is a flocculent spiral galaxy situated in the constellation of Eridanus. Located about 75 million light years away, it is a member of the Eridanus cluster of galaxies, a cluster of about 200 galaxies. It was discovered by William Herschel on 19 December 1799.
SN 2020oi was a supernova event in the grand design spiral galaxy known as Messier 100, or NGC 4321. It was discovered January 7, 2020 at an apparent magnitude of 17.28 by F. Forster and associates using the Zwicky Transient Facility. The position places it ~4.67″ north of the galactic nucleus. The supernova was not detected on an observation made three days before the discovery, and thus it must have begun during that brief period. The light curve peaked around January 13–18, depending on the wavelength, then declined rapidly over a period of 25 days before flattening into a more gradual decline. Observations of the spectrum made with the SOAR telescope showed this to be a type Ic supernova, with the progenitor being a massive star that had its outer envelope stripped. The initial velocity of the expanding photosphere was ~15,000 km/s.
