In astronomy, a calcium-rich supernova (or Calcium-rich transient, Ca-rich SN) is a subclass of

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

e that, in contrast to more well-known traditional supernova classes, are fainter and produce unusually large amounts of

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

. Since their

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

is located in a gap between that of

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

e and other supernovae, they are also referred to as "gap"

transients Transience or transient may refer to: Music * ''Transient'' (album), a 2004 album by Gaelle * ''Transience'' (Steven Wilson album), 2015 * Transience (Wreckless Eric album) Science and engineering * Transient state, when a process variable o ...

. Only around 15 events have been classified as a calcium-rich supernova (as of August 2017) – a combination of their intrinsic rarity and low

make new discoveries and their subsequent study difficult. This makes calcium-rich supernovae one of the most mysterious supernova subclasses currently known.

Origins and classification

A peculiar group of supernova that were unusually rich in calcium were identified by Alexei Filippenko and collaborators. Although they appeared somewhat similar to

Type Ib and Ic supernovae Type Ib and Type Ic supernovae are categories of supernovae that are caused by the stellar core collapse of massive stars. These stars have shed or been stripped of their outer envelope of hydrogen, and, when compared to the spectru ...

, their spectra were dominated by calcium, without other signatures often seen in Type Ib and Ic supernovae, and the term ''calcium-rich'' was coined to describe them. Subsequent discoveries led to the classification of empirically similar supernovae. They share characteristics such as quickly rising and fading

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

s that peak in luminosity between novae and supernovae, and spectra that are dominated by calcium 2–3 months after initial explosion.

Explosion mechanism

The exact nature of the stellar systems and their subsequent explosions that give rise to calcium-rich supernovae are unknown. Despite appearing similar to Type Ib supernovae, it was noted that a different explosion mechanism was likely to be responsible for calcium-rich supernovae. Since a large proportion of the

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...

from which they are thought to originate are early-type galaxies, and thus composed of old

stellar population In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926. Baade observed tha ...

s, they are unlikely to contain many young, massive

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

s that give rise to Type Ib supernovae. Supernova explosions in old stellar populations generally involved a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

since these are old systems that can undergo thermonuclear explosion under the right circumstances, as is the case for

Type Ia supernova A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) 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 ...

e. However, because calcium-rich supernovae are much less luminous and fade more quickly than normal Type Ia supernovae, it is unlikely that the same mechanism is at play for both. Another peculiarity of calcium-rich supernovae is that they appear to explode far away from galaxies, even reaching intergalactic space. Searches for faint

dwarf galaxies A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is so ...

at their locations have ruled that they are exploding in very low density environments, unlike other supernova types. There are several theories that attempt to explain this behaviour.

Binary systems Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two values (0 and 1) for each digit * Binary function, a function that takes two arguments * Binary operation, a mathematical op ...

of high-velocity stars, such as two white dwarfs or a white dwarf and a

neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...

, that have been ejected from their galaxy either due to a neutron star kick or interaction with the

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...

in their galaxy could produce explosions when they eventually merge (due to

gravitational wave Gravitational waves are oscillations of the gravitational field that Wave propagation, travel through space at the speed of light; they are generated by the relative motion of gravity, gravitating masses. They were proposed by Oliver Heaviside i ...

radiation) that would preferentially occur far from galaxies. Alternatively they have been suggested to be due to stars that reside in the

intracluster medium In astronomy, the intracluster medium (ICM) is the superheated plasma (physics), plasma that permeates a galaxy cluster. The gas consists mainly of ionized hydrogen and helium and accounts for most of the baryonic material in galaxy clusters. The ...

within large galaxy groups or clusters, having been expelled from their galaxy during

mergers Mergers and acquisitions (M&A) are business transactions in which the ownership of a company, business organization, or one of their operating units is transferred to or consolidated with another entity. They may happen through direct absorpt ...

or interactions. The explosion would then be caused by the detonation of a low mass white dwarf during a merging event as part of a binary system, or the detonation of a

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

shell on a white dwarf. A calcium-rich supernova event expels several tenths of a

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

in material at thousands of kilometres per second and reaches a peak luminosity equal to around 100–200 million times that of the Sun. Despite calcium-rich supernovae being comparatively rare and diminutive compared to other supernova types, they are thought to make a significant contribution to the production of calcium in the

Universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

List

References

External links

List of all known Type Ca-rich supernovae
a
The Open Supernova Catalog
. {{Supernovae Supernovae