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Ultra-stripped supernovae occur when the exploding star has been stripped (almost) all the way to the metal core, via mass transfer in a close binary. [128] [129] As a result, very little material is ejected from the exploding star (c. 0.1 M ☉). In the most extreme cases, ultra-stripped supernovae can occur in naked metal cores, barely above the Chandrasekhar mass limit. SN 2005ek [130] might be the first observational example of an ultra-stripped supernova, giving rise to a relatively dim and fast decaying light curve. The nature of ultra-stripped supernovae can be both iron core-collapse and electron capture supernovae, depending on the mass of the collapsing core. Ultra-stripped supernovae are believed to be associated with the second supernova explosion in a binary system, producing for example a tight double neutron star system. [131] [132]

Type Ib supernovae are the more common and result from Wolf–Rayet stars of type WC which still have helium in their atmospheres. For a narrow range of masses, stars evolve further before reaching core collapse to become WO stars with very little helium remaining, and these are the progenitors of type Ic supernovae. [124]Large numbers of supernovae have been catalogued and classified to provide distance candles and test models. [157] [158] Average characteristics vary somewhat with distance and type of host galaxy, but can broadly be specified for each supernova type. The core collapse of some massive stars may not result in a visible supernova. This happens if the initial core collapse cannot be reversed by the mechanism that produces an explosion, usually because the core is too massive. These events are difficult to detect, but large surveys have detected possible candidates. [138] [139] The red supergiant N6946-BH1 in NGC 6946 underwent a modest outburst in March 2009, before fading from view. Only a faint infrared source remains at the star's location. [140] Light curves [ edit ] Typical light curves for several types of supernovae; in practice, magnitude and duration varies within each type. See Karttunen et al. for types Ia, Ib, II-L and II-P; [141] Modjaz et al. for types Ic and IIb; [142] and Nyholm et al. for type IIn. [143] The last supernova directly observed in the Milky Way was Kepler's Supernova in 1604, appearing not long after Tycho's Supernova in 1572, both of which were visible to the naked eye. The remnants of more recent supernovae have been found, and observations of supernovae in other galaxies suggest they occur in the Milky Way on average about three times every century. A supernova in the Milky Way would almost certainly be observable through modern astronomical telescopes. The most recent naked-eye supernova was SN 1987A, which was the explosion of a blue supergiant star in the Large Magellanic Cloud, a satellite of the Milky Way. Louk’s mother, Ricarda, later said: “This morning my daughter, Shani Nicole Louk, a German citizen, was kidnapped with a group of tourists in southern Israel by Palestinian Hamas.

A knot in the central ring of Supernova 1987A, as observed by the Hubble Space Telescope in 1994 (left) and 1997 (right).The knot is caused by the collision of the supernova's blast wave with a slower-moving ring of matter it had ejected earlier. The bright spot on the lower left is an unrelated star. (more)Type IIn supernovae are characterised by additional narrow spectral lines produced in a dense shell of circumstellar material. Their light curves are generally very broad and extended, occasionally also extremely luminous and referred to as a superluminous supernova. These light curves are produced by the highly efficient conversion of kinetic energy of the ejecta into electromagnetic radiation by interaction with the dense shell of material. This only occurs when the material is sufficiently dense and compact, indicating that it has been produced by the progenitor star itself only shortly before the supernova occurs. [155] [156]

A white dwarf star may accumulate sufficient material from a stellar companion to raise its core temperature enough to ignite carbon fusion, at which point it undergoes runaway nuclear fusion, completely disrupting it. There are three avenues by which this detonation is theorised to happen: stable accretion of material from a companion, the collision of two white dwarfs, or accretion that causes ignition in a shell that then ignites the core. The dominant mechanism by which type Ia supernovae are produced remains unclear. [74] Despite this uncertainty in how type Ia supernovae are produced, type Ia supernovae have very uniform properties and are useful standard candles over intergalactic distances. Some calibrations are required to compensate for the gradual change in properties or different frequencies of abnormal luminosity supernovae at high redshift, and for small variations in brightness identified by light curve shape or spectrum. [75] [76] Normal Type Ia [ edit ] This Chandra X-ray photograph shows Cassiopeia A (Cas A, for short), the youngest supernova remnant in the Milky Way. (Image credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.) Type I supernovas This stunning view of M101, also known as the Pinwheel galaxy, is one of the largest images Hubble has ever captured of a spiral galaxy, assembled from 51 exposures taken during various studies over nearly ten years. Ground-based images were used to fill in the portions of the galaxy that Hubble did not observe. (Image credit: Hubble Image: NASA, ESA, K. Kuntz (JHU), F. Bresolin (University of Hawaii), J. Trauger (Jet Propulsion Lab), J. Mould (NOAO), Y.-H. Chu (University of Illinois, Urbana) and STScI; CFHT Image: Canada-France-Hawaii Telescope/J.-C. Cuillandre/Coelum; NOAO Image: G. Jacoby, B. Bohannan, M. Hanna/NOAO/AURA/NSF) In 2008, scientists caught a supernova in the act of exploding for the first time. While peering at her computer screen, astronomer Alicia Soderberg expected to see the small glowing smudge of a month-old supernova. But what she and her colleague saw instead was a strange, extremely bright, five-minute burst of X-rays.Supernovae can be brighter than an entire galaxy. One single supernova can easily outshine an entire galaxy of stars in its release of a single burst of energy. In a short period of time, it mightgenerate more energy than what our sunmight generate in its entire 10 billion-year lifespan. In 2022 a team of astronomers led by researchers from the Weizmann Institute of Science reported the first supernova explosion showing direct evidence for a Wolf-Rayet progenitor star. SN 2019hgp was a type Icn supernova and is also the first in which the element neon has been detected. [133] [134] Electron-capture supernovae [ edit ]

Either type of supernova can be so bright as to briefly outshine an entire galaxy. But Type II supernovas are particularly interesting because they release not only light but also enormous numbers of neutrinos. In fact, the emission of neutrinos can start a little bit ahead of the explosion itself, explains Kate Scholberg, an astronomer at Duke University. The so-called classic explosion, associated with Type II supernovae, has as progenitor a very massive star (a Population I star) of at least eight solar masses that is at the end of its active lifetime. (These are seen only in spiral galaxies, most often near the arms.) Until this stage of its evolution, the star has shone by means of the nuclear energy released at and near its core in the process of squeezing and heating lighter elements such as hydrogen or helium into successively heavier elements—i.e., in the process of nuclear fusion. Forming elements heavier than iron absorbs rather than produces energy, however, and, since energy is no longer available, an iron core is built up at the centre of the aging, heavyweight star. When the iron core becomes too massive, its ability to support itself by means of the outward explosive thrust of internal fusion reactions fails to counteract the tremendous pull of its own gravity. Consequently, the core collapses. If the core’s mass is less than about three solar masses, the collapse continues until the core reaches a point at which its constituent nuclei and free electrons are crushed together into a hard, rapidly spinning core. This core consists almost entirely of neutrons, which are compressed in a volume only 20 km (12 miles) across but whose combined weight equals that of several Suns. A teaspoonful of this extraordinarily dense material would weigh 50 billion tons on Earth. Such an object is called a neutron star.Astronomers use Type Ia supernovas as "standard candles" to measure cosmic distances because all are thought to blaze with equal brightness at their peaks. In type II-L the plateau is absent because the progenitor had relatively little hydrogen left in its atmosphere, sufficient to appear in the spectrum but insufficient to produce a noticeable plateau in the light output. In type IIb supernovae the hydrogen atmosphere of the progenitor is so depleted (thought to be due to tidal stripping by a companion star) that the light curve is closer to a type I supernova and the hydrogen even disappears from the spectrum after several weeks. [62] Imagine that you’re an astronomer in the early years of the 17th century. The telescope hasn’t yet been invented, so you scan the night sky only with the unaided eye. Then one day you see a remarkable sight: A bright new star appears, and for the next few weeks it outshines even the planet Venus. It’s so bright it can even be seen in broad daylight. It lingers in the sky for many months, gradually dimming over time. When 1987A blew up, neutrino science was in its infancy—even so, two dozen neutrinos were recorded by three detectors working at the time. If a supernova explodes within our galaxy now, the global network of detectors will record hundreds or even thousands of neutrinos.