A second model for the formation of type Ia supernovae involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit. [88] This is sometimes referred to as the double-degenerate model, as both stars are degenerate white dwarfs. Due to the possible combinations of mass and chemical composition of the pair there is much variation in this type of event, [89] and, in many cases, there may be no supernova at all, in which case they will have a less luminous light curve than the more normal SN type Ia. [90] Non-standard Type Ia [ edit ]

In other words, it’s been a long wait—418 years since we’ve seen a star explode in our galaxy. So are we overdue for a bright, nearby supernova? Historical supernovae are known simply by the year they occurred: SN 185, SN 1006, SN 1054, SN 1572 (called Tycho's Nova) and SN 1604 ( Kepler's Star). [58] Since 1885 the additional letter notation has been used, even if there was only one supernova discovered that year (for example, SN 1885A, SN 1907A, etc.); this last happened with SN 1947A. SN, for SuperNova, is a standard prefix. Until 1987, two-letter designations were rarely needed; since 1988, they have been needed every year. Since 2016, the increasing number of discoveries has regularly led to the additional use of three-digit designations. [59] Classification [ edit ]

Types of supernovas

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] If you are hoping to catch a look at M101 or anything else in the night sky, our guides to the best telescopesand best binocularsare a great place to start. The closest and most easily observed of the hundreds of supernovae that have been recorded since 1604 was first sighted on the morning of Feb. 24, 1987, by the Canadian astronomer Ian K. Shelton while working at the Las Campanas Observatory in Chile. Designated SN 1987A, this formerly extremely faint object attained a magnitude of 4.5 within just a few hours, thus becoming visible to the unaided eye. The newly appearing supernova was located in the Large Magellanic Cloud at a distance of about 160,000 light-years. It immediately became the subject of intense observation by astronomers throughout the Southern Hemisphere and was observed by the Hubble Space Telescope. SN 1987A’s brightness peaked in May 1987, with a magnitude of about 2.9, and slowly declined in the following months. Types of supernovae

It is now known by direct observation that much of the light curve (the graph of luminosity as a function of time) after the occurrence of a type II Supernova, such as SN 1987A, is explained by those predicted radioactive decays. [8] Although the luminous emission consists of optical photons, it is the radioactive power absorbed by the ejected gases that keeps the remnant hot enough to radiate light. The radioactive decay of 56Ni through its daughters 56Co to 56Fe produces gamma-ray photons, primarily with energies of 847 keV and 1,238keV, that are absorbed and dominate the heating and thus the luminosity of the ejecta at intermediate times (several weeks) to late times (several months). [147] Energy for the peak of the light curve of SN1987A was provided by the decay of 56Ni to 56Co (half-life 6 days) while energy for the later light curve in particular fit very closely with the 77.3-day half-life of 56Co decaying to 56Fe. Later measurements by space gamma-ray telescopes of the small fraction of the 56Co and 57Co gamma rays that escaped the SN 1987A remnant without absorption confirmed earlier predictions that those two radioactive nuclei were the power sources. [146] Messier 61 with supernova SN2020jfo, taken by an amateur astronomer in 2020 There are several means by which a supernova of this type can form, but they share a common underlying mechanism. If a carbon- oxygen white dwarf accreted enough matter to reach the Chandrasekhar limit of about 1.44 solar masses [77] (for a non-rotating star), it would no longer be able to support the bulk of its mass through electron degeneracy pressure [78] [79] and would begin to collapse. However, the current view is that this limit is not normally attained; increasing temperature and density inside the core ignite carbon fusion as the star approaches the limit (to within about 1%) [80] before collapse is initiated. [77] In contrast, for a core primarily composed of oxygen, neon and magnesium, the collapsing white dwarf will typically form a neutron star. In this case, only a fraction of the star's mass will be ejected during the collapse. [79] The blue spot at the centre of the red ring is an isolated neutron star in the Small Magellanic Cloud.Let's look at the more exciting Type II first. For a star to explode as a Type II supernova, it must be several times more massive than the sun (estimates run from eight to 15 solar masses). Like the sun, it will eventually run out of hydrogen and then helium fuel at its core. However, it will have enough mass and pressure to fuse carbon.