A 'supernova' (plural: ''supernovae'' or ''supernovas'') is a
stellar explosion that creates an extremely
luminous object. A supernova causes a burst of radiation that may briefly outshine its entire host
galaxy before fading from view over several weeks or months. During this short interval, the supernova
radiates as much
energy as the
Sun would emit over 10 billion years.
[1] The explosion expels much or all of a star's material
[2] at a velocity of up to a tenth the
speed of light, driving a
shock wave into the surrounding
interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a
supernova remnant.
Several types of supernovae exist that may be triggered in one of two ways, involving either turning off or suddenly turning on the production of energy through
nuclear fusion. After the core of an
aging massive star ceases to generate energy from nuclear fusion, it may undergo sudden
gravitational collapse into a
neutron star or
black hole, releasing
gravitational potential energy that heats and expels the star's outer layers. Alternatively, a
white dwarf star may accumulate sufficient material from a
stellar companion (usually through
accretion, rarely via a merger) to raise its core temperature enough to
ignite carbon fusion, at which point it undergoes
runaway nuclear fusion, completely disrupting it. Stellar cores whose furnaces have permanently gone out collapse when their masses exceed the
Chandrasekhar limit, while accreting white dwarfs ignite as they approach this limit (roughly 1.38
[3] times the
mass of the Sun). White dwarfs are also subject to a different, much smaller type of thermonuclear explosion
fueled by hydrogen on their surfaces called a
nova. Solitary stars with a mass below approximately nine
es, such as the Sun itself, evolve into white dwarfs without ever becoming supernovae.
On average, supernovae occur about once every 50 years in a galaxy the size of the
Milky Way[4] and play a significant role in enriching the interstellar medium with heavy
elements. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.
[5]
''Nova'' (plural ''novae'') means "new" in
Latin, referring to what appears to be a very bright new star shining in the
celestial sphere; the
prefix "super" distinguishes supernovae from ordinary
novae, which also involve a star increasing in brightness, though to a lesser extent and through a different mechanism. According to ''
Merriam-Webster's Collegiate Dictionary'', the word ''supernova'' was first used in print in 1926.
Observation history
Main articles: History of supernova observation
The earliest recorded supernova,
SN 185, was viewed by
Chinese astronomers in
AD 185. The widely observed supernova of
SN 1054 produced the
Crab Nebula. Supernovae
SN 1572 and
SN 1604, the last to be observed in the
Milky Way galaxy, had notable effects on the development of astronomy in Europe because they were used to argue against the
Aristotelian idea that the world beyond the Moon and planets was immutable.
[6]
Since the development of the
telescope, the field of supernova discovery has enlarged to other galaxies, starting with the 1885 observation of supernova
S Andromedae in the
Andromeda galaxy. Supernovae provide important information on cosmological distances.
[7] During the twentieth century, successful models for each type of supernova were developed, and scientists' comprehension of the role of supernovae in the star formation process is growing.
Some of the most distant supernovae recently observed appeared dimmer than expected.
This has provided evidence that the expansion of the
universe may be accelerating.
[8][9]
Discovery
Because supernovae are relatively rare events, occurring about once every 50 years in a galaxy like the Milky Way,
4 many galaxies must be monitored regularly in order to obtain a good sample of supernovae to study.
Supernovae in other galaxies cannot be predicted with any meaningful accuracy. When they are discovered, they are already in progress.
[10] Most scientific interest in supernovae—as
standard candles for measuring distance, for example—require an observation of their peak luminosity. It is therefore important to discover them well before they reach their maximum.
Amateur astronomers, who greatly outnumber professional astronomers, have played an important role in finding supernovae, typically by looking at some of the closer galaxies through an
optical telescope and comparing them to earlier photographs.
Towards the end of the 20th century, astronomers increasingly turned to computer-controlled telescopes and
CCDs for hunting supernovae. While such systems are popular with amateurs, there are also larger installations like the
Katzman Automatic Imaging Telescope.
[11] Recently, the
Supernova Early Warning System (SNEWS) project has also begun using a network of
neutrino detectors to give early warning of a supernova in the Milky Way galaxy.
[12][13] A neutrino is a
particle that is produced in great quantities by a supernova explosion,
[14] and it is not obscured by the interstellar gas and dust of the galactic disk.
Supernova searches fall into two classes: those focused on relatively nearby events and those looking for explosions farther away. Because of the
expansion of the universe, the distance to a remote object with a known emission spectrum can be estimated by measuring its
Doppler shift (or
redshift); on average, more distant objects recede with greater velocity than those nearby, and so have a higher redshift. Thus the search is split between high redshift and low redshift, with the boundary falling around a redshift range of ''z'' = 0.1–0.3
[15]—where ''z'' is a dimensionless measure of the spectrum's frequency shift.
High redshift searches for supernovae usually involve the observation of supernova light curves. These are useful for standard or calibrated candles to generate Hubble diagrams and make cosmological predictions. At low redshift, supernova spectroscopy is more practical than at high redshift, and this is used to study the physics and environments of supernovae.
[16][17] Low redshift observations also anchor the low distance end of the Hubble curve, which is a plot of distance versus redshift for visible galaxies.
[18][19]
Naming convention
Supernova discoveries are reported to the
International Astronomical Union's
Central Bureau for Astronomical Telegrams, which sends out a circular with the name it assigns to it. The name is formed by the year of discovery, immediately followed by a one or two-letter designation. The first 26 supernovae of the year get designated with an upper case letter from A to Z. Afterward, pairs of lower-case letters are used, starting with aa, ab, and so on.
[20] Professional and amateur astronomers find several hundred supernovae per year (in recent years: 367 in 2005 and 551 in 2006). For example, the last supernova of 2005 was SN 2005nc, indicating that it was the 367
th supernova found in 2005.
[21][22]
Historical supernovae are known simply by the year they occurred:
SN 185,
SN 1006,
SN 1054,
SN 1572 (Tycho's Nova), and
SN 1604 (Kepler's Star). Beginning in 1885, the letter notation is used, even if there was only one supernova discovered that year (e.g. SN 1885A, 1907A, etc.)—this last happened with SN 1947A. The standard abbreviation "SN" is an optional prefix.
Classification
As part of the attempt to understand supernovae, astronomers have classified them according to the
absorption lines of different chemical elements that appear in their
spectra. The first element for a division is the presence or absence of a line caused by
hydrogen. If a supernova's spectrum contains a line of hydrogen (known as the
Balmer series in the visual portion of the spectrum) it is classified ''Type II''; otherwise it is ''Type I''. Among those types, there are subdivisions according to the presence of lines from other elements and the shape of the
light curve (a graph of the supernova's
apparent magnitude ''versus'' time).
[23]
Supernova taxonomy[24]| Type | Characteristics |
|---|
| Type I |
| Type Ia | Lacks hydrogen and presents a singly-ionized silicon (Si II) line at 615.0 nm (nanometers), near peak light. |
| Type Ib | Non-ionized helium (He I) line at 587.6 nm and no strong silicon absorption feature near 615 nm. |
| Type Ic | Weak or no helium lines and no strong silicon absorption feature near 615 nm. |
| Type II | |
| Type IIP | Reaches a "plateau" in its light curve |
| Type IIL | Displays a "linear" decrease in its light curve (linear in magnitude versus time).[25] |
The supernovae of Type II can also be sub-divided based on their spectra. While most Type II supernova show very broad
emission lines which indicate expansion velocities of many thousands of
kilometres per second, some have relatively narrow features. These are called Type IIn, where the "n" stands for "narrow".
24
A few supernovae, such as SN 1987K and SN 1993J, appear to change types: they show lines of hydrogen at early times, but, over a period of weeks to months, become dominated by lines of helium. The term "Type IIb" is used to describe the combination of features normally associated with Types II and Ib.
24
Current models
Type Ia
Main articles: Type Ia supernova
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 1.38
solar masses
(for a non-rotating star), it would no longer be able to support the bulk of its plasma through
electron degeneracy pressure[26][27] and would begin to collapse. However, the current view is that this limit is not normally attained; increasing temperature inside the core
ignites carbon fusion as the star approaches the limit, before collapse is initiated.
Within a few seconds, a substantial fraction of the matter in the white dwarf undergoes nuclear fusion, releasing enough energy (1–2 × 10
44 joules)
[28] to unbind the star in a supernova explosion.
[29] An outwardly expanding
shock wave is generated, with matter reaching velocities on the order of 5,000–20,000 km/s, or roughly 3% of the speed of light. There is also a significant increase in luminosity, reaching an
absolute magnitude of -19.3 (or 5 billion times brighter than the Sun), with little variation.
[30]
One model for the formation of this category of supernova is a close
binary star system. The larger of the two stars is the first to evolve off the
main sequence, and it expands to form a
red giant.
[31] The two stars now share a common envelope, causing their mutual orbit to shrink. The giant star then sheds most of its envelope, losing mass until it can no longer continue
nuclear fusion. At this point it becomes a white dwarf star, composed primarily of carbon and oxygen.
[6][33] Eventually the secondary star also evolves off the main sequence to form a red giant. Matter from the giant is accreted by the white dwarf, causing the latter to increase in mass.
Another model for the formation of a Type Ia explosion involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit.
[34] A white dwarf could also accrete matter from other types of companions, including a main sequence star (if the orbit is sufficiently close).
Type Ia supernovae follow a characteristic
light curve—the graph of luminosity as a function of time—after the explosion. This luminosity is generated by the
radioactive decay of
nickel-56 through
cobalt-56 to
iron-56.
30 The peak luminosity of the light curve is consistent across Type Ia supernovae (the vast majority of which are initiated with a uniform mass via the accretion mechanism), allowing them to be used as a secondary
[35] standard candle to measure the distance to their host
galaxies.
[36]
Type Ib and Ic
Main articles: Type Ib and Ic supernovae
These events, like supernovae of Type II, are probably massive stars running out of fuel at their centers; however, the progenitors of Types Ib and Ic have lost most of their outer (hydrogen) envelopes due to strong
stellar winds or else from interaction with a companion.
[6] Type Ib supernovae are thought to be the result of the collapse of a massive
Wolf-Rayet star. There is some evidence that a few percent of the Type Ic supernovae may be the progenitors of
gamma ray bursts (GRB), though it is also believed that any hydrogen-stripped, Type Ib or Ic supernova could be a GRB, dependent upon the geometry of the explosion.
[38]
Type II
Main articles: Type II supernova
The onion-like layers of a massive, evolved star just prior to core collapse. (Not to scale.)
Stars with at least nine
solar masses of material evolve in a complex fashion.
[39] In the core of the star, hydrogen is fused into helium, releasing the energy needed to support the overlaying layers against collapse (see
hydrostatic equilibrium). Once the core's supply of hydrogen is exhausted, the core contracts until the temperature and pressure rise high enough to allow helium fusion. As the star evolves, it undergoes repeated stages where fusion in the core stops, and the core collapses until conditions allow ignition of the next stage of fusion, temporarily halting further collapse.
Fusion of lighter elements continues to occur in shells surrounding the core at radii where the required conditions and fuel are found. These stars become layered like onions, with the burning of more easily fused elements occurring in larger shells. The outermost shell fuses hydrogen to create helium, which is fused to create carbon in the next lower shell, and so forth.
[40][41]
As increasingly heavier elements undergo nuclear fusion, the
binding energy of the nuclei increases and progressively lower levels of energy are produced. This culminates with the
production of nickel-56, which does not produce energy through fusion (but does produce iron-56 through radioactive decay).
[42] As a result, a nickel-iron core
[43] builds up that can only support the overlaying mass of the star through the
degeneracy pressure of
electrons. When the core's size exceeds the Chandrasekhar limit, degeneracy pressure can no longer support it and a catastrophic collapse ensues.
26
Core collapse
The core implodes at velocities reaching 70,000 km/s (0.23
c),
[44] resulting in a rapid increase in temperature and density. Through
photodisintegration,
gamma rays decompose the iron into helium nuclei and free
neutrons. The conditions also cause
electrons and
protons to merge through
electron capture, producing neutrons and electron
neutrinos. About 10
46 joules of gravitational energy are converted into a ten-second burst of neutrinos.
[45] These carry away energy from the core and accelerate the collapse, while some neutrinos are absorbed by the star's outer layers and begin the supernova explosion.
[46]
The inner core eventually reaches a density comparable to that of an
atomic nucleus, where the collapse is halted. The infalling matter then rebounds, producing a shock wave that propagates outward. Computer simulations indicate that this expanding shock will stall in the outer core as energy is lost through the dissociation of heavy elements, and that a process that is not clearly understood is necessary to allow the shock to reabsorb 10
44 joules (1
foe) of energy, producing an explosion.
[47]
Within a massive, evolved star (a) the onion-layered shells of elements undergo fusion, forming an iron core (b) that reaches Chandrasekhar-mass and starts to collapse. The inner part of the core is compressed into neutrons (c), causing infalling material to bounce (d) and form an outward-propagating shock front (red). The shock starts to stall (e), but it is re-invigorated by neutrino interaction. The surrounding material is blasted away (f), leaving only a degenerate remnant.
When the progenitor star is below about 20
solar masses (depending on the strength of the explosion and the amount of material that falls back), the degenerate remnant of a core collapse is a
neutron star.
44 Above this mass the remnant collapses to form a
black hole.
41[48] (This type of collapse is one of many candidate explanations for
gamma ray bursts—producing a large burst of
gamma rays through a still theoretical
hypernova explosion.)
[49] The theoretical limiting mass for this type of core collapse scenario was estimated around 40–50 solar masses.
Above 50 solar masses, stars were believed to collapse directly into a black hole without forming a supernova explosion,
[50] although uncertainties in models of supernova collapse make accurate calculation of these limits difficult. In fact recent evidence has shown stars in the range of about 140–250 solar masses, with a relatively low proportion of elements more massive than helium, may be capable of forming
pair-instability supernovae without leaving behind a black hole remnant. This rare type of supernova is formed by an alternate mechanism (partially analogous to that of Type Ia explosions) that does not require an iron core. An example is the Type II supernova
SN 2006gy, with an estimated 150 solar masses, that demonstrated the explosion of such a massive star differed fundamentally from previous theoretical predictions.
[51][52]
Light curves and unusual spectra
This graph of the luminosity (relative to the Sun) as a function of time shows the characteristic shapes of the light curves for a Type II-L and II-P supernova.
The light curves for Type II supernovae are distinguished by the presence of hydrogen
Balmer absorption lines in the spectra. These light curves have an average decay rate of 0.008
magnitudes per day; much lower than the decay rate for Type I supernovae. Type II are sub-divided into two classes, depending on whether there is a plateau in their light curve (Type II-P) or a linear decay rate (Type II-L). The net decay rate is higher at 0.012 magnitudes per day for Type II-L compared to 0.0075 magnitudes per day for Type II-P. The difference in the shape of the light curves is believed to be caused, in the case of Type II-L supernovae, by the expulsion of most of the hydrogen envelope of the progenitor star.
25
The plateau phase in Type II-P supernovae is due to a change in the
opacity of the exterior layer. The shock wave
ionizes the hydrogen in the outer envelope, which greatly increases the opacity. This prevents photons from the inner parts of the explosion from escaping. Once the hydrogen cools sufficiently to recombine, the outer layer becomes transparent.
[53]
Of the Type II supernovae with unusual features in their spectra, Type IIn supernovae may be produced by the interaction of the ejecta with circumstellar material.
[54] Type IIb supernovae are likely massive stars which have lost most, but not all, of their hydrogen envelopes through
tidal stripping by a companion star. As the ejecta of a Type IIb expands, the hydrogen layer quickly becomes optically thin and reveals the deeper layers.
[55]
Asymmetry
A long-standing puzzle surrounding supernovae has been a need to explain why the compact object remaining after the explosion is given a large velocity away from the core.
[56] (
Neutron stars are observed, as
pulsars, to have high velocities;
black holes presumably do as well, but are far harder to observe in isolation.) This kick can be substantial, propelling an object of more than a
solar mass at a velocity of 500 km/s or greater. This displacement is believed to be caused by an asymmetry in the explosion, but the mechanism by which this momentum is transferred to the compact object has remained a puzzle. Some explanations for this kick include convection in the collapsing star and jet production during neutron star formation.
This composite image shows
X-ray (blue) and optical (red) radiation from the
Crab Nebula's core region. A
pulsar near the center is propelling particles to almost the speed of light.
[57] This neutron star is travelling at an estimated 375 km/s.
[58] ''
NASA/CXC/HST/ASU/J. Hester'' et al. ''image credit.''
One explanation for the asymmetry in the explosion is large-scale convection above the core. The convection can create variations in the local abundances of elements, resulting in uneven nuclear burning during the collapse, bounce and resulting explosion.
[59]
Another explanation is that accretion of gas onto the central neutron star can create a
disk that drives highly directional jets, propelling matter at a high velocity out of the star, and driving transverse shocks that completely disrupt the star. These jets might play a crucial role in the resulting supernova explosion.
[60][61] (A similar model is now favored for explaining long
gamma ray bursts.)
Initial asymmetries have also been confirmed in Type Ia supernova explosions through observation. This result may mean that the initial luminosity of this type of supernova may depend on the viewing angle. However, the explosion becomes more symmetrical with the passage of time. Early asymmetries are detectable by measuring the polarization of the emitted light.
[62]
Type Ia versus core collapse
Because they have a similar functional model, Types Ib, Ic and various Types II supernovae are collectively called Core Collapse supernovae. A fundamental difference between Type Ia and Core Collapse supernovae is the source of energy for the radiation emitted near the peak of the light curve. The progenitors of Core Collapse supernovae are stars with extended envelopes that can attain a degree of transparency with a relatively small amount of expansion. Most of the energy powering the emission at peak light is derived from the shock wave that heats and ejects the envelope.
[6]
The progenitors of Type Ia supernovae, on the other hand, are compact objects, much smaller (but more massive) than the Sun, that must expand (and therefore cool) enormously before becoming transparent. Heat from the explosion is dissipated in the expansion and is not available for light production. The radiation emitted by Type Ia supernovae is thus entirely attributable to the decay of
radionuclides produced in the explosion; principally
nickel-56 (with a half-life of 6.1 days) and its daughter
cobalt-56 (with a half-life of 77 days). Gamma rays emitted during this
nuclear decay are absorbed by the ejected material, heating it to
incandescence.
As the material ejected by a Core Collapse supernova expands and cools, radioactive decay eventually takes over as the main energy source for light emission in this case also. A bright Type Ia supernova may expel 0.5–1.0
solar masses of nickel-56,
[64] while a Core Collapse supernova probably ejects closer to 0.1 solar mass of nickel-56.
[65]
Interstellar impact
Source of heavy elements
Main articles: Supernova nucleosynthesis
Supernovae are a key source of
elements heavier than
oxygen. These elements are produced by
nuclear fusion (for
iron-56 and lighter elements), and by
nucleosynthesis during the supernova explosion for elements heavier than iron. Supernova are the most likely, although not undisputed, candidate sites for the
r-process, which is a rapid form of nucleosynthesis that occurs under conditions of high temperature and high density of neutrons. The reactions produce highly unstable
nuclei that are rich in
neutrons. These forms are unstable and rapidly
beta decay into more stable forms.
The r-process reaction, which is likely to occur in type II supernovae, produces about half of all the element abundance beyond iron, including
plutonium,
uranium and
californium.
[66] The only other major competing process for producing elements heavier than iron is the
s-process in large, old red giant stars, which produces these elements much more slowly, and which cannot produce elements heavier than
lead.
[67]
Role in stellar evolution
Main articles: Supernova remnant
The remnant of a supernova explosion consists of a compact object and a rapidly expanding
shock wave of material. This cloud of material sweeps up the surrounding
interstellar medium during a free expansion phase, which can last for up to two centuries. The wave then gradually undergoes a period of
adiabatic expansion, and will slowly cool and mix with the surrounding interstellar medium over a period of about 10,000 years.
[2]
In standard astronomy, the
Big Bang produced
hydrogen,
helium, and traces of
lithium, while all heavier elements are synthesized in stars and supernovae. Supernovae tend to enrich the surrounding
interstellar medium with ''metal''s, which for astronomers means all of the elements other than hydrogen and helium and is a different definition than that used in chemistry.
These injected elements ultimately enrich the
molecular clouds that are the sites of star formation.
[69] Thus, each stellar generation has a slightly different composition, going from an almost pure mixture of hydrogen and helium to a more metal-rich composition. Supernovae are the dominant mechanism for distributing these heavier elements, which are formed in a star during its period of nuclear fusion, throughout space. The different abundances of elements in the material that forms a star have important influences on the star's life, and may decisively influence the possibility of having
planets orbiting it.
The
kinetic energy of an expanding supernova remnant can trigger star formation due to compression of nearby, dense molecular clouds in space. The increase in turbulent pressure can also prevent star formation if the cloud is unable to lose the excess energy.
[70]
Evidence from daughter products of short-lived
radioactive isotopes shows that a nearby supernova helped determine the composition of the
Solar System 4.5 billion years ago, and may even have triggered the formation of this system.
[71] Supernova production of heavy elements over astronomic periods of time ultimately made the
chemistry of life on Earth possible.
Impact on Earth
A 'near-Earth supernova' is an explosion resulting from the death of a
star that occurs close enough to the Earth (roughly fewer than 100
light-years away) to have noticeable effects on its
biosphere.
Gamma rays are responsible for most of the adverse effects a supernova can have on a living
terrestrial planet. In Earth's case, gamma rays induce a
chemical reaction in the upper
atmosphere, converting molecular
nitrogen into
nitrogen oxides, depleting the
ozone layer enough to expose the surface to harmful
solar and
cosmic radiation. The
gamma ray burst from a nearby supernova explosion has been proposed as the cause of the
end Ordovician extinction, which resulted in the death of nearly 60% of the oceanic life on Earth.
[72]
Speculation as to the effects of a nearby supernova on Earth often focuses on large stars as Type II supernova candidates. Several prominent stars within a few hundred light years from the Sun are candidates for becoming supernovae in as little as a millennium. One example is
Betelgeuse, a red supergiant 427 light-years from Earth.
[73] Though spectacular, these "predictable" supernovae are thought to have little potential to affect Earth.
Recent estimates predict that a Type II supernova would have to be closer than eight
parsecs (26 light-years) to destroy half of the Earth's ozone layer.
[74] Such estimates are mostly concerned with atmospheric modeling and considered only the known radiation flux from
SN 1987A, a Type II supernova in the
Large Magellanic Cloud. Estimates of the rate of supernova occurrence within 10 parsecs of the Earth vary from once every 100 million years
[75] to once every one to ten billion years.
[76]
Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common
white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied. One theory suggests that a Type Ia supernova would have to be closer than a thousand parsecs (3300 light-years) to affect the Earth.
[77] The closest known candidate is
IK Pegasi (see below).
[78]
In 1996, astronomers at the
University of Illinois at Urbana-Champaign theorized that traces of past supernovae might be detectable on Earth in the form of metal isotope signatures in
rock strata. Subsequently,
iron-60 enrichment has been reported in deep-sea rock of the
Pacific Ocean by researchers from the
Technical University of Munich.
[79][80][81]
Milky Way candidates
Several large stars within the
Milky Way have been suggested as possible supernovae within the next few thousand to hundred million years. These include
Rho Cassiopeiae,
[83] Eta Carinae,
[84][85] RS Ophiuchi,
[86][87] the Kitt Peak Downes star KPD1930+2752,
[88] HD 179821,
[89][90] IRC+10420,
[91] VY Canis Majoris,
[92] Betelgeuse,
Antares, and
Spica.
73
Many
Wolf-Rayet stars, such as
Gamma Velorum,
[93] WR 104,
[94] and those in the Quintuplet Cluster,
[95] are also considered possible precursor stars to a supernova explosion in the 'near' future.
The nearest supernova candidate is
IK Pegasi (HR 8210), located at a distance of only 150 light-years. This closely-orbiting
binary star system consists of a main sequence star and a
white dwarf, separated by only 31 million
km. The dwarf has an estimated mass equal to 1.15 times that of the Sun.
[96] It is thought that several million years will pass before the white dwarf can accrete the critical mass required to become a Type Ia supernova.
[97][98]
See also
★
Supernova remnant
★
List of supernova remnants
★
Dwarf nova
★
Timeline of white dwarfs, neutron stars, and supernovae
★
Champagne Supernova (astronomy)
Notes
- 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.[99]
- Per the American Physical Society Neutrino Study reference,45 roughly 99% of the gravitational potential energy is released as neutrinos of all flavors. The remaining 1% is equal to 1044 J
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Modulations in the radio light curve of the Type IIb supernova 2001ig: evidence for a Wolf-Rayet binary progenitor?, S. D. Ryder ''et al'', , , Monthly Notices of the Royal Astronomical Society, 2004
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Further reading
★
SUPERNOVAE. By what mechanism do massive stars explode?, Hans Bethe, , , Physics Today,
★
The Alchemy of the Heavens: Searching for Meaning in the Milky Way, , Ken, Croswell, Anchor Books, 1996, ISBN 0385472145 —a popular-science account.
★ —an article describing spectral classes of supernovae.
★
Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star, Takahashi, K.; Sato, K.; Burrows, A.; Thompson, T. A., , , Physical Review D, 2003 —a good review of supernova events.
★
How to Blow Up a Star, , Wolfgang, Hillebrandt, Scientific American,
★ —link is to a pre-print of the article submitted to ''
Nature''.
External links
★
List of Supernovae-related Web pages.
★
RSS news feed
★
Sternberg Astronomical Institute Supernova Catalogue D. Yu. Tsvetkov, N. N. Pavlyuk, O. S. Bartunov, Yu. P. Pskovskii —a searchable catalog.
★
BoomCode Anonymous —Boom Code—Professional-grade type II supernova simulator on Wikiversity.
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