Supernova - SpeedyLook encyclopedia

Etymology

The term of “supernova” is resulting from the term of “nova”, drawn from the Latin nova , meaning “new”. Historically, it is in 1572 then in 1604 that the western world realizes that “new stars” appear sometimes, for a time limited on the Vault of heaven. These events were described respectively by Tycho Brahé and Johannes Kepler in Latin writings using the term of stella nova (see for example De Stella Nova in Fag Serpentarii , of Kepler, published in 1606). Thereafter, the temporary appearance of new stars was called under the term of “nova”. These events hide in fact two classes of distinct phenomena: it can be a question is of an explosion thermomucléaire occurring with the surface of a star after this one had accrété of the matter resulting from another star, explosion not destroying the star which is the seat, that is to say the complete explosion of a star. The distinction between these two phenomena was made in the current of the Années 1930. The last being largely energy than the first, it is this one which took the name of Nova previously used, whereas the second took the name of supernova. The term itself was employed for the first time by Walter Baade and Fritz Zwicky in 1933 at the time of the annual convention of the American company of physics. The older writings speaking about the observation of supernovas still use the term of nova: it is for example the case of the reports/ratios of observation of the last supernova observed, in 1885, in the Galaxie of Andromède, SN 1885A (see the references in the article corresponding).

Spectral classification

Historically, the supernovas were classified according to their spectrum, according to two types, noted by the Roman numerals I and II, which contain several sub-types:

the supernovas of standard I have a spectrum which does not contain a Hydrogène
the supernovas of standard II have a spectrum which contains hydrogen.

Among the supernovas of the type I, one distinguishes three subclasses:

If the spectrum shows the presence of Silicium, one speaks about standard Ia
If the spectrum does not show the presence of silicon, one looks at the abundance of Hélium:

In the presence of a notable quantity of helium, one speaks about standard Ib
In the presence of small quantity of helium, one speaks about standard Ic

Concerning the supernovas of the type II, one considers then the spectrum approximately three months after the beginning of the explosion:

If the spectrum shows that helium dominates over hydrogen, one speaks about standard IIb
If the spectrum shows that hydrogen dominates over helium, one speaks about standard II “normal” , this one being divided into the last two sub-types:

If the Courbe of light decrease linearly after the maximum, one says that one has a standard IIL (for “linear”)
If the curve of light shows a plate marqu" , or a phase of slow decrease, one speaks about standard IIP (for “plate”)

This classification is actually rather far away from the subjacent reality of these objects. There exist two physical mechanisms giving place to a supernova:

the supernovas known as thermonuclear correspond only to the type Ia
the supernovas called to collapse of heart correspond to all the other types. The term of supernovas of the type II is sometimes wrongly used to indicate the whole of these objects, whereas they can be Ib type or Ic. In that, the term of supernova to collapse of heart is preferable with that of “type II”, more ambiguous. The spectral differences between the supernovas with collapse of heart come primarily owing to the fact that the star formed part or not of a Binary system. The supernovas of the normal type II do not form part of a binary system, or then their companion does not affect their evolution significantly. The other types (Ib, Ic, IIb) are on the other hand resulting from various types of interaction between star and his/her companion.

General principle

Cataclysmic event signing the end of a star, a supernova can result from two types of very different events:

the thermonuclear explosion of a white Dwarf following a Accretion of matter torn off with a close star (even a collision with this one) which explodes completely (supernova known as thermonuclear);
the gravitational collapse of a massive star (supernova called to collapse of heart). This collapse occurs when the heart of star consists of Fer. This element being most stable, its fusion or its Fission, consume energy instead of producing some. When this iron heart is formed, the star does not have any more an energy source generating a Pression of sufficient radiation to support the roadbases, which crush the heart then: the heart of star is compressed and the iron cores are then dissociated, the Proton S capturing the electron S forming of the Neutron S. This new heart of neutrons, much more compact is then able to resist the compression of the external layers by the quantum Pression of degeneration what stops their collapse brutally. The energy released by the internal layers falling towards the center, produces a shock wave which “blows” the layers external of star, forming gas of the Rémanent of the supernova.

Type of the supernovas

The astronomers distributed the supernovas in various classes, according to the elements which appear in their electromagnetic Specter.

The principal element using concerned classification is the presence or not of Hydrogène. If the spectrum of a supernova does not contain hydrogen, it is classified standard I, if not type II. Among these groups, there are subdivisions compared to other elements.

Type I

The supernovas of the Ia type do not have a Hélium present in their spectrum but of the Silicium. It is generally thought that they are caused by the explosion of a white Naine approaching or having reached the Limite of Chandrasekhar by Accrétion of matter. A possible scenario explaining this phenomenon is dwarf white orbits about it around a fairly massive star. The dwarf one attracts the matter of his/her companion until it reaches the Limite of Chandrasekhar. Then, the internal pressure of star having become insufficient to thwart its clean revolved, the dwarf one starts to crumble. This collapse allows the lighting of the fusion of the atoms of Carbone and Oxygène which composes star, and this fusion is not controlled any more by the heating and the dilation of star, as for stars of the principal Séquence (the pressure of star is that of its degenerated electrons, calculated by Fermi). It then occurs a racing of the reactions of fusion which disintegrates the dwarf one in a gigantic thermonuclear explosion. This is different from the mechanism of formation of a Nova where the dwarf white one does not reach the Limite of Chandrasekhar, but begins a nuclear fusion of the matter accumulated and compressed on the surface. The increase in luminosity is due to the energy released by the explosion and is maintained the time necessary with the disintegration of the Cobalt in Fer.

The variation of the luminosity of star during a supernova of the Ia type being extremely regular, these supernovas can be used like cosmic candles. In 1998, it is by the observation of supernovas of the Ia type in galaxies moved away, that the physicists discovered that the Expansion of the universe accelerated.

The supernovas of the Ib type and Ic do not show silicon in their spectrum and one does not know yet the mechanism of their formation. The supernovæ of the type Ic do not show either helium in their spectrum. One thinks that they correspond to stars at the end of the lifetime (like type II) and who would have already exhausted their hydrogen, of this fact hydrogen does not appear on their spectrum. The supernovas of the Ib type are surely the result of the collapse of a star Wolf-Rayet. A bond with the starts long gamma seems established.

Type II

The ultimate phase of the life of a massive star (more than 8 solar masses) starts after the nickel-56 and iron heart was built by successive phases of reactions fusion nuclear. These elements being most stable, the reactions of fusion, as of nuclear fission of iron consume energy instead of producing some. Deprived of its energy source, the heart becomes unable to support the weight of the external layers: it starts to contract. It reaches (or reached already) the density to which the Pression of degeneration of the electrons dominates (~ 1 tonne/cm). The layer directly enclosing the heart become inert however continues to produce iron and nickel on the surface of the heart whose mass thus continues to increase until it reaches the “mass of Chandrasekhar” (approximately 1,4 solar masses). At this moment, the pressure of degeneration of the electrons is exceeded and a phase of neutronisation of a few seconds leads to the collapse of the heart. The electrons are captured by the protons, generating a massive flow of electronic neutrinos, and transforming the heart into a neutron star 10-20 km in diameter and density of an atomic nucleus (> 100 million tonnes/cm).

It is this gravitational contraction of the heart in neutronisation and those of the adjacent internal layers which release all the energy of the explosion of the supernova. It is an explosion due to the release of energy of the gravitational potential which increases during this collapse, exceeding several times all the Potentiel nuclear power of hydrogen to iron (~ 0,9% of the energy of mass). This energy is transmitted towards outside according to various phenomena like: the shock wave, the heating of the matter, and especially the flow of neutrinos.

When the thermal pressure reaches the level of degeneration of the Nucléon S, the external layers of the heart rebound to 10 20% speed of light. The shock wave of the rebound is propagated towards the external layers and enters in competition with the matter falling towards the interior, in such way that it is stabilized around 100-200 km of the center. The neutrinos diffuse out of the heart in a few seconds and a fraction of them heats the zone of the coat located inside the shock wave (called “area of profit”). The remainder is released in space, carrying 99% of the total energy of the supernova. It is thought nowadays, that the contribution of energy to the shock wave by the heating of the area of profit due to the neutrinos is the key component responsible for the explosion of the supernova.

In massive stars, during the last moments of the explosion, the high temperatures (> 10 9 K) allow the “process R”: a great density of neutrons (10 20 n/cm 3 ) made that their capture by the cores is faster than the radioactive Décroissance β^-), because that occurs in a few seconds. Thus isotopes rich in neutrons of Atomic number occurs quite higher than that of iron (NR = 26). And is explained the existence of heavy radioactive cores in the Univers; like the Thorium and the Uranium always present on Ground of share their Half-life S about the age of the Solar system.

There exist also tiny alternatives of these various types, with designations such as II-P and II-L , but they describe simply the behavior of the evolution of the luminosity (II-P observes a plate whereas II-L not) and not of the fundamental data.

Hypernovas

Some exceptionally massive stars can produce a “Hypernova” when they crumble, a type of explosion relatively new and highly theoretical. In a hypernova, the heart of star crumbles directly in a black hole because it became more massive than the limit of “neutron stars”. Two extremely energy jets of plasma are emitted along the axis of rotation of star at a speed close to that of the light.

These jets emit intense gamma rays and could explain the origin of the starts gamma. Indeed, if the observer is in (or close to) the axis of the jets, it will receive a signal which could be collected since the fine bottom of the Univers (cosmological Horizon). -->

Luminosity

The supernovas of the type I are, all things considered, considerably more brilliant than those of type II. This in electromagnetic luminosity.

Name of the supernovas

The discoveries of supernovas are declared with the international astronomical Union, which sends a circular with the name that it assigns to him. The name is formed by the year of discovered and a reference of one or two letters. The 26 first supernovas of the year have a letter between has and Z; after Z, they start with aa, ab, and so on. For example, SN 1987A, the most famous supernova undoubtedly of modern times, which was observed on February 23rd 1987 in the Grand Cloud of Magellan, was the first discovered this year.

Supernovas remarkable

See too

Physics of the supernovas

thermonuclear Supernova
Supernova with collapse of heart
Supernova with production of pairs
stellar Nucleosynthesis
Remanent of supernova

Search for supernovas

External bonds

popularization

Supernovas: the explosive death of stars, 110 minutes video conference (Nicolas Prantzos with the Institute of Astrophysics of Paris).
list of recent supernovas on the site of Harvard-Smithsonian Center for Astrophysics

Random links:

Helmut Höflehner | Meadow of the Rock | Charles Emile Seurre | Kōzō Fuyutsuki | Aime de Lemud