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Type Ib and Type Ic supernovae are categories 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 are caused by the stellar core collapse of massive stars. These stars have shed or been stripped of their outer envelope of
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
, and, when compared to the spectrum of Type Ia supernovae, they lack the
absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...
of silicon. Compared to Type Ib, Type Ic supernovae are hypothesized to have lost more of their initial envelope, including most of their helium.


Spectra

When a
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 ...
is observed, it can be categorized in the MinkowskiZwicky supernova classification scheme based upon the
absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...
s that appear in its
spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
. A supernova is first categorized as either a Type I or Type II, then subcategorized based on more specific traits. Supernovae belonging to the general category Type I lack
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
lines in their spectra; in contrast to Type II supernovae which do display lines of hydrogen. The Type I category is subdivided into Type Ia, Type Ib and Type Ic. Type Ib/Ic supernovae are distinguished from Type Ia by the lack of an
absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...
of singly ionized
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
at a
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of 635.5 
nanometre 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling), is a unit of length ...
s. As Type Ib and Ic supernovae age, they also display lines from elements such as
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
,
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 ...
and
magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
. In contrast, Type Ia spectra become dominated by lines of
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
. Type Ic supernovae are distinguished from Type Ib in that the former also lack lines of
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 ...
at 587.6 nm.


Formation

Prior to becoming a supernova, an evolved massive star is organized like an onion, with layers of different elements undergoing fusion. The outermost layer consists of hydrogen, followed by helium, carbon, oxygen, and so forth. Thus when the outer envelope of hydrogen is shed, this exposes the next layer that consists primarily of helium (mixed with other elements). This can occur when a very hot, massive star reaches a point in its evolution when significant mass loss is occurring from its
stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...
. Highly massive stars (with 25 or more times the mass of the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
) can lose up to 10−5
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 ...
es () each year—the equivalent of every 100,000 years. Type Ib and Ic supernovae are hypothesized to have been produced by core collapse of massive stars that have lost their outer layer of hydrogen and helium, either via winds or mass transfer to a companion. The progenitors of Types Ib and Ic have lost most of their outer envelopes due to strong
stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...
s or else from interaction with a close companion of about . Rapid mass loss can occur in the case of a
Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectroscopy, spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very ...
, and these massive objects show a spectrum that is lacking in hydrogen. Type Ib progenitors have ejected most of the hydrogen in their outer atmospheres, while Type Ic progenitors have lost both the hydrogen and helium shells; in other words, Type Ic have lost more of their envelope (i.e., much of the helium layer) than the progenitors of Type Ib. In other respects, however, the underlying mechanism behind Type Ib and Ic supernovae is similar to that of a Type II supernova, thus placing Types Ib and Ic between Type Ia and Type II. Because of their similarity, Type Ib and Ic supernovae are sometimes collectively called Type Ibc supernovae. There is some evidence that a small fraction of the Type Ic supernovae may be the progenitors of gamma ray bursts (GRBs); in particular, type Ic supernovae that have broad spectral lines corresponding to high-velocity outflows are thought to be strongly associated with GRBs. However, it is also hypothesized that any hydrogen-stripped Type Ib or Ic supernova could be a GRB, dependent upon the geometry of the explosion. In any case, astronomers believe that most Type Ib, and probably Type Ic as well, result from core collapse in stripped, massive stars, rather than from the thermonuclear runaway of
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 ...
s. As they are formed from rare, very massive stars, the rate of Type Ib and Ic supernova occurrence is much lower than the corresponding rate for Type II supernovae. They normally occur in regions of new star formation, and are extremely rare in
elliptical galaxies An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Re ...
. Because they share a similar operating mechanism, Type Ibc and the various Type II supernovae are collectively called core-collapse supernovae. In particular, Type Ibc may be referred to as ''stripped core-collapse supernovae''.


Light curves

The
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 (a plot of luminosity versus time) of Type Ib supernovae vary in form, but in some cases can be nearly identical to those of Type Ia supernovae. However, Type Ib light curves may peak at lower luminosity and may be redder. In the
infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
portion of the spectrum, the light curve of a Type Ib supernova is similar to a Type II-L light curve. Type Ib supernovae usually have slower decline rates for the spectral curves than Ic. Type Ia supernovae light curves are useful for measuring distances on a cosmological scale. That is, they serve as
standard candle The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...
s. However, due to the similarity of the spectra of Type Ib and Ic supernovae, the latter can form a source of contamination of supernova surveys and must be carefully removed from the observed samples before making distance estimates.


See also

* Type Ia supernova * Type II supernova


References


External links


List of all known Type Ib and Ic supernovae
a
The Open Supernova Catalog
. {{good article Type 1b and 1c Supernova