- Amateur Astronomy
- Astrobiology (134)
- Astrophysics (79)
- Black Holes (38)
- Cosmology (204)
- Dark Matter, Dark Energy (13)
- Galaxies (37)
- History of Astronomy (37)
- Nebulae (19)
- Observational astronomy (107)
- 1. Space Observatories (10)
- 1.1 Chandra X-Ray (63)
- 1.2 Hubble telescope (9)
- 1.3 Kepler Mission (11)
- Solar System (124)
- Small Solar System Bodies (SSSB) (30)
- Space Exploration (90)
- 1. NASA (9)
- 1.1 NASA Human Spaceflight (15)
- 1.1.1 NASA Apollo Program (18)
- 22.214.171.124 The Astronauts (13)
- 126.96.36.199 The Apollo Spacecraft (23)
- 188.8.131.52 The Apollo 7 (14)
- 184.108.40.206 The Apollo 8 (8)
- 220.127.116.11 The Apollo 9 (1)
- 18.104.22.168 The Apollo 10 (1)
- 22.214.171.124 The Apollo 11 (79)
- 1.1.2 NASA Shuttle Program (104)
- 126.96.36.199 STS-127 (20)
- 188.8.131.52 STS-128 (56)
- 184.108.40.206 STS-129 (89)
- 220.127.116.11 STS-130 (10)
- 18.104.22.168 STS-131 (81)
- 22.214.171.124 STS-132 (77)
- 1.1.3 NASA Constellation Program (36)
- 1.2 NASA Uncrewed Missions (17)
- 1.2.a Solar Missions (20)
- 1.2.b Lunar Missions (7)
- 1.2.c Mercury missions (3)
- 1.2.d Venus Missions (4)
- 1.2.e Mars Missions (29)
- 1.2.f Jupiter Missions (10)
- 1.2.g Saturn Missions (17)
- 1.2.h Uranus Missions (2)
- 1.2.i Neptune Missions (4)
- 1.2.j Pluto Missions (3)
- 1.2.k Interplanetary Missions (8)
- 1.2.l Boeing X-37 (12)
- 1.3 Expendable Launch Systems (1)
- 2. International Space Station (7)
- 2.1 ISS Assembly (25)
- Stars (31)
- Supernovae (8)
Supernova (pl. supernovae) is a stellar explosion. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this short interval, a supernova can radiate as much energy as the Sun could emit over its life span. The explosion expels much or all of a star's material at a velocity of up to 30,000 km/s (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 kinds of supernovae exist that may be triggered in one of two ways, 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 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 solar masses, 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. They play a significant role in enriching the interstellar medium with higher mass elements. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.
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 and was coined by Swiss astrophysicist and astronomer, Fritz Zwicky.
The earliest recorded supernova, SN 185, was viewed by Chinese astronomers in 185 AD. The brightest recorded supernova was the SN 1006, which was described in detail by Chinese and Arab astronomers. The widely observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the last to be observed with the naked eye 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 universe beyond the Moon and planets was immutable.
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. 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.
In the 1960s, astronomers found that the maximum intensities of supernova explosions could be used as distance indicators. 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. New techniques were developed for reconstructing supernova explosions that have no written records of being observed. The date of the Cassiopeia A supernova event was determined from light echoes off nebulae, while the age of supernova remnant RX J0852.0-4622 was estimated from temperature measurements and the gamma ray emissions from the decay of titanium-44. In 2009, nitrates were discovered in Antarctic ice deposits that corresponded to past supernova events.
Because supernovae are relatively rare events within a galaxy, occurring about once every 50 years in the Milky Way, obtaining a good sample of supernovae to study requires regular monitoring of many galaxies.
Supernovae in other galaxies cannot be predicted with any meaningful accuracy. Normally, when they are discovered, they are already in progress. 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. 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. Neutrinos are particles that are produced in great quantities by a supernova explosion, and they are not significantly absorbed 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—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. Low redshift observations also anchor the low distance end of the Hubble curve, which is a plot of distance versus redshift for visible galaxies.
See also: Hubble's law
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. Professional and amateur astronomers find several hundreds of supernovae each year (367 in 2005, 551 in 2006 and 572 in 2007). For example, the last supernova of 2005 was SN 2005nc, indicating that it was the 367th[nb 1] supernova found in 2005.
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). Since 1885, the letter notation was 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.
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).
- 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 IIP Reaches a "plateau" in its light curve
- Type IIL Displays a "linear" decrease in its light curve (linear in magnitude versus time).
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'. Supernovae that do not fit into the normal classifications are designated peculiar, or 'pec'.
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.
There are several means by which a supernova of this type can form, but they share a common underlying mechanism. If a carbon-oxygen[nb 2] 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 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%), 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 × 1044 joules) to unbind the star in a supernova explosion. 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.
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. 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. 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. 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. The peak luminosity of the light curve was believed to be consistent across Type Ia supernovae (the vast majority of which are initiated with a uniform mass via the accretion mechanism), having a maximum absolute magnitude of about -19.3. This would allow them to be used as a secondary standard candle to measure the distance to their host galaxies. However, recent discoveries reveal that there is some evolution in the average lightcurve width, and thus in the intrinsic luminosity of Supernovae, although significant evolution is found only over a large redshift baseline.
Type Ib and Ic
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. 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.
Stars with at least nine solar masses of material evolve in a complex fashion. In the core of the star, hydrogen is fused into helium and the thermal energy released creates an outward pressure, which maintains the core in hydrostatic equilibrium and prevents collapse.
When the core's supply of hydrogen is exhausted, this outward pressure is no longer created. The core begins to collapse, causing a rise in temperature and pressure which becomes great enough to ignite the helium and start a helium-to-carbon fusion cycle, creating sufficient outward pressure to halt the collapse. The core expands and cools slightly, with a hydrogen-fusion outer layer, and a hotter, higher pressure, helium-fusion center. (Other elements such as magnesium, sulfur and calcium are also created and in some cases burned in these further reactions.)
This process repeats several times, and each time the core collapses and the collapse is halted by the ignition of a further process involving more massive nuclei and higher temperatures and pressures. Each layer is prevented from collapse by the heat and outward pressure of the fusion process in the next layer inward; each layer also burns hotter and quicker than the previous one—the final burn of silicon to nickel consumes its fuel in around one day, or a few days. The star becomes layered like an onion, with the burning of more easily fused elements occurring in larger shells.
In the later stages, increasingly heavier elements undergo nuclear fusion, and the binding energy of the relevant nuclei increases. Fusion produces progressively lower levels of energy, and also at higher core energies photodisintegration and electron capture occur which cause energy loss in the core and a general acceleration of the fusion processes to maintain hydrostatic equilibrium. This escalation culminates with the production of nickel-56, which is unable to produce energy through fusion (but does produce iron-56 through radioactive decay). As a result, a nickel-iron core builds up that cannot produce any further outward pressure on a scale needed to support the rest of the structure. It can only support the overlaying mass of the star through the degeneracy pressure of electrons in the core. If the star is sufficiently large, then the iron-nickel core will eventually exceed the Chandrasekhar limit (1.38 solar masses), at which point this mechanism catastrophically fails. The forces holding atomic nuclei apart in the innermost layer of the core suddenly give way, the core implodes due to its own mass, and no further fusion process can ignite or prevent collapse this time.
The core collapses in on itself with velocities reaching 70,000 km/s (0.23c), resulting in a rapid increase in temperature and density. The energy loss processes operating in the core cease to be in equilibrium. Through photodisintegration, gamma rays decompose iron into helium nuclei and free neutrons, absorbing energy, whilst electrons and protons merge via electron capture, producing neutrons and electron neutrinos which escape.
In a typical Type II supernova, the newly formed neutron core has an initial temperature of about 100 billion kelvin (100 GK); 6000 times the temperature of the sun's core. Much of this thermal energy must be shed for a stable neutron star to form (otherwise the neutrons would "boil away"), and this is accomplished by a further release of neutrinos. These 'thermal' neutrinos form as neutrino-antineutrino pairs of all flavors, and total several times the number of electron-capture neutrinos. About 1046 joules of gravitational energy—approximately 10% of the star's rest mass—is converted into a ten-second burst of neutrinos; the main output of the event. These carry away energy from the core and accelerate the collapse, while some neutrinos may be later absorbed by the star's outer layers to provide energy to the supernova explosion.
The inner core eventually reaches typically 30 km diameter, and a density comparable to that of an atomic nucleus, and further collapse is abruptly stopped by strong force interactions and by degeneracy pressure of neutrons. The infalling matter, suddenly halted, rebounds, producing a shock wave that propagates outward. Computer simulations indicate that this expanding shock does not directly cause the supernova explosion; rather, it stalls within milliseconds in the outer core as energy is lost through the dissociation of heavy elements, and a process that is not clearly understood is necessary to allow the outer layers of the core to reabsorb around 1044 joules[nb 3] (1 foe) of energy, producing the visible explosion. Current research focuses upon a combination of neutrino reheating, rotational and magnetic effects as the basis for this process.
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 a process that may include 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. Above this mass the remnant collapses to form a black hole. (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.) 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, 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.
Light curves and unusual spectra
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.
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.
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. 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.
The peak absolute magnitude of Type II supernovae is not constant, but they are dimmer than Type Ia. For instance, the low-luminosity SN 1987A had a peak visual absolute magnitude of -15.5 (apparent magnitude +3 for a distance of 51 kpc), as compared to the standard -19.3 for Type Ia.
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. (Neutron stars are observed, as pulsars, to have high velocities; black holes presumably do as well, but are far harder to observe in isolation.) The initial impetus 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.
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.
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. (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.
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.
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, while a Core Collapse supernova probably ejects closer to 0.1 solar mass of nickel-56.
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. Supernovae 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. 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.
Role in stellar evolution
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.
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 metals, which for astronomers means all of the elements other than hydrogen and helium and is a different definition than that used in chemistry.
Supernova remnant N 63A lies within a clumpy region of gas and dust in the Large Magellanic Cloud. NASA image.
These injected elements ultimately enrich the molecular clouds that are the sites of star formation. 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.
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. 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 from a supernova 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. This 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. In 1996, it was 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.
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. The closest known candidate is IK Pegasi (see below). 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.
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, Eta Carinae, RS Ophiuchi, U Scorpii, the Kitt Peak Downes star KPD1930+2752, HD 179821, IRC+10420, VY Canis Majoris, Betelgeuse, Antares, and Spica.
Many Wolf-Rayet stars, such as Gamma Velorum, WR 104, and those in the Quintuplet Cluster, 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 150 light-years. This closely orbiting binary star system consists of a main sequence star and a white dwarf, separated by 31 million kilometres. The dwarf has an estimated mass equal to 1.15 times that of the Sun. 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.
1. The value is obtained by converting the suffix "nc" from base 26, with a=1, b=2, c=3, ... n=14, ... z=26. Thus nc = n×26+c = 14×26+3 = 367.
2. 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.
See: Fryer, C. L.; New, K. C. B. (2006-01-24). "2.1 Collapse scenario". Gravitational Waves from Gravitational Collapse. Max-Planck-Gesellschaft. http://www.livingreviews.org/Articles/Volume6/2003-2new. Retrieved 2007-06-07.
3. Per the American Physical Society Neutrino Study reference, Barwick, Beacom et al. (2004), roughly 99% of the gravitational potential energy is released as neutrinos of all flavors. The remaining 1% is equal to 1044 J
1. Giacobbe, F. W. (2005). "How a Type II Supernova Explodes". Electronic Journal of Theoretical Physics 2 (6): 30–38. http://adsabs.harvard.edu/abs/2005EJTP....2f..30G. Retrieved 2007-08-03.
2. "Introduction to Supernova Remnants". NASA Goddard Space Flight Center. 2006-07-27. http://heasarc.gsfc.nasa.gov/docs/objects/snrs/snrstext.html... Retrieved 2006-09-07.
3. Schawinski, K. Justham, S.; Wolf, C.; Podsiadlowski, P.; Sullivan, M.; Steenbrugge, K. C.; Bell, T.; Röser, H.-J.; Walker, E. S.; Astier, P.; Balam, D.; Balland, C.; Carlberg, R.; Conley, A.; Fouchez, D.; Guy, J.; Hardin, D.; Hook, I.; Howell, D. A.; Pain, R.; Perrett, K.; Pritchet, C.; Regnault, N.; Yi, S. K. (2008). "Supernova Shock Breakout from a Red Supergiant". Science Express 321: 223. doi:10.1126/science.1160456. PMID 18556514.
4. a b c Mazzali, P. A.; K. Röpke, F. K.; Benetti, S.; Hillebrandt, W. (2007). "A Common Explosion Mechanism for Type Ia Supernovae". Science 315 (5813): 825–828. doi:10.1126/science.1136259. PMID 17289993.
5. a b "Integral identifies supernova rate for Milky Way". European Space Agency. 2006-01-04. http://www.esa.int/SPECIALS/Integral/SEMACK0VRHE_0.html. Retrieved 2007-02-02.
6. Whittet, Doug C. B. (2003). Dust in the Galactic Environment. CRC Press. pp. 45–46. ISBN 0750306246.
7. a b Krebs, J.; Hillebrandt, W. (1983). "The interaction of supernova shockfronts and nearby interstellar clouds". Astronomy and Astrophysics 128 (2): 411–419. http://adsabs.harvard.edu/abs/1983A&A...128..411K. Retrieved 2007-02-01.
8. Allen, Jesse (1998-02-02). "Supernova Effects". NASA. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980202b.... Retrieved 2007-02-02.
9. Boss, Alan P.; Ipatov, Sergei I.; Keiser, Sandra A.; Myhill, Elizabeth A.; Vanhala, Harri A. T.. "Simultaneous Triggered Collapse of the Presolar Dense Cloud Core and Injection of Short-Lived Radioisotopes by a Supernova Shock Wave". The Astrophysical Journal 686 (2): L119–122. doi:10.1086/593057. Bibcode: 2008ApJ...686L.119B.
10. "supernova". Merriam-Webster's Online Collegiate Dictionary. http://www.merriam-webster.com/dictionary/supernova. Retrieved 10 June 2009.
11. Clark, D. H.; Stephenson, F. R. (1981-06-29). "The Historical Supernovae". Supernovae: A survey of current research; Proceedings of the Advanced Study Institute. Cambridge, England: Dordrecht, D. Reidel Publishing Co... pp. 355–370.
12. van Zyl, Jan Eben (2003). "VARIABLE STARS VI". Astronomical Society of Southern Africa. http://www.aqua.co.za/assa_jhb/new/canopus/can2003/c039litu.... Retrieved 2006-09-27.
13. Kowal, C. T. (1968). "Absolute magnitudes of supernovae". Astronomical Journal 73: 1021–1024. doi:10.1086/110763. http://adsabs.harvard.edu/cgi-bin/bib_query?1968AJ.....73.10... Retrieved 2008-06-04.
14. Leibundgut, B.; Sollerman, J. (2001). "A cosmological surprise: the universe accelerates". Europhysics News 32 (4): 121. doi:10.1051/epn:2001401. http://www.eso.org/~bleibund/papers/EPN/epn.html. Retrieved 2007-02-01.
15. "Confirmation of the accelerated expansion of the Universe". Centre National de la Recherche Scientifique. 2003-09-19. http://www2.cnrs.fr/en/45.htm?&debut=160xt/. Retrieved 2006-11-03.
16. Fabian, Andrew C. (2008). "A Blast from the Past". Nature 320 (5880): 1167–1168. doi:10.1126/science.1158538.
17. Aschenbach, Bernd (1998-11-12). "Discovery of a young nearby supernova remnant". Letters to Nature 396: 141–142. doi:10.1038/24103.
18. Iyudin, A. F. et al. (November 1998). "Emission from 44Ti associated with a previously unknown Galactic supernova". Nature 396 (6707): 142–144. doi:10.1038/24106.
19. "Ancient supernovae found written into the Antarctic ice". New Scientist (2698). 2009-03-04. http://www.newscientist.com/article/mg20126984.800-ancient-s... Retrieved 2009-03-09.
20. Bishop, David. "Latest Supernovae". Rochester's Astronomy Club. http://www.rochesterastronomy.org/snimages/. Retrieved 2006-11-28.
21. Evans, Robert O. (1993). "Supernova Search Manual, 1993". American Association of Variable Star Observers (AAVSO). http://www.aavso.org/observing/programs/sn/. Retrieved 2006-10-05.
22. Antonioli, P. et al. (2004). "SNEWS: the SuperNova Early Warning System". New Journal of Physics 6: 114. doi:10.1088/1367-2630/6/1/114. http://stacks.iop.org/1367-2630/6/114. Retrieved 2006-11-28.
23. "SNWES: Supernova Early Warning System". National Science Foundation. http://snews.bnl.gov/. Retrieved 2006-11-28.
24. Beacom, J. F. (1999). Supernova Neutrinos and the Neutrino Masses. http://arxiv.org/abs/hep-ph/9901300. Retrieved 2006-11-28.
25. Frieman, Josh (2006). "SDSS Supernova Survey". SDSS. http://sdssdp47.fnal.gov/sdsssn/sdsssn.html. Retrieved 2006-08-10.
26. Perlmutter, Saul. "High Redshift Supernova Search". Lawrence Berkeley National Laboratory. http://www-supernova.lbl.gov/public/. Retrieved 2006-10-09.
27. Linder, E. V.; Huterer, D. (2003). "Importance of supernovae at z>1.5 to probe dark energy". Physical Review D 67 (8): 081303. doi:10.1103/PhysRevD.67.081303. http://adsabs.harvard.edu/abs/2002astro.ph..8138L. Retrieved 2007-02-01.
28. Perlmutter, S. et al. (1997). "Measurements of the Cosmological Parameters Ω and Λ from the First Seven Supernovae at z >= 0.35". Astrophysical Journal 483: 565. doi:10.1086/304265. http://adsabs.harvard.edu/abs/1997ApJ...483..565P. Retrieved 2007-02-01.
29. Aldering, Greg (2005-12-01). "The Nearby Supernova Factory". Lawrence Berkeley National Laboratory. http://snfactory.lbl.gov/. Retrieved 2006-12-01.
30. "List of Recent Supernovae". Harvard-Smithsonian Center for Astrophysics. http://www.cfa.harvard.edu/iau/lists/RecentSupernovae.html. Retrieved 2007-10-16.
31. "List of Supernovae". International Astronomical Union (IAU) Central Bureau for Astronomical Telegrams. http://www.cfa.harvard.edu/iau/lists/Supernovae.html. Retrieved 2007-10-16.
32. "The Padova-Asiago supernova catalogue". Astronomical Observatory of Padua. http://web.oapd.inaf.it/supern/snean.txt. Retrieved 2006-11-28.
33. Cappellaro, E.; Turatto, M. (2000-08-08). "Supernova Types and Rates". Influence of Binaries on Stellar Population Studies. Brussels, Belgium: Dordrecht: Kluwer Academic Publishers.
34. a b c Montes, M. (2002-02-12). "Supernova Taxonomy". Naval Research Laboratory. http://rsd-www.nrl.navy.mil/7212/montes/snetax.html. Retrieved 2006-11-09.
35. a b Doggett, J. B.; Branch, D. (1985). "A Comparative Study of Supernova Light Curves". Astronomical Journal 90: 2303–2311. doi:10.1086/113934. http://adsabs.harvard.edu/abs/1985AJ.....90.2303D. Retrieved 2007-02-01.
36. a b Lieb, E. H.; Yau, H.-T. (1987). "A rigorous examination of the Chandrasekhar theory of stellar collapse". Astrophysical Journal 323 (1): 140–144. doi:10.1086/165813. http://adsabs.harvard.edu/abs/1987ApJ...323..140L. Retrieved 2007-02-01.
37. Canal, R.; Gutiérrez, J. (1997). "The possible white dwarf-neutron star connection". Astrophysics and Space Science Library 214: 49. http://adsabs.harvard.edu/abs/1997astro.ph..1225C. Retrieved 2007-02-01.
38. Wheeler, J. Craig (2000-01-15). Cosmic Catastrophes: Supernovae, Gamma-Ray Bursts, and Adventures in Hyperspace. Cambridge, UK: Cambridge University Press. pp. 96. ISBN 0521651956. http://www.cambridge.org/catalogue/catalogue.asp?isbn=978052...
39. Khokhlov, A.; Mueller, E.; Hoeflich, P. (1993). "Light curves of Type IA supernova models with different explosion mechanisms". Astronomy and Astrophysics 270 (1–2): 223–248. http://adsabs.harvard.edu/cgi-bin/bib_query?1993A%26A...270.... Retrieved 2007-05-22.
40. Röpke, F. K.; Hillebrandt, W. (2004). "The case against the progenitor's carbon-to-oxygen ratio as a source of peak luminosity variations in Type Ia supernovae". Astronomy and Astrophysics 420: L1–L4. doi:10.1051/0004-6361:20040135.
41. a b Hillebrandt, W.; Niemeyer, J. C. (2000). "Type IA Supernova Explosion Models". Annual Review of Astronomy and Astrophysics 38: 191–230. doi:10.1146/annurev.astro.38.1.191. http://adsabs.harvard.edu/abs/2000ARA&A..38..191H. Retrieved 2007-02-01.
42. Richmond, Michael. "Late stages of evolution for low-mass stars". Rochester Institute of Technology. http://spiff.rit.edu/classes/phys230/lectures/planneb/planne... Retrieved 2006-08-04.
43. Paczynski, B. (July 28 – August 1, 1975). "Common Envelope Binaries". Structure and Evolution of Close Binary Systems. Cambridge, England: Dordrecht, D. Reidel Publishing Co.. pp. 75–80.
44. Postnov, K. A.; Yungelson; L. R. (2006). "The Evolution of Compact Binary Star Systems". Living Reviews in Relativity. http://relativity.livingreviews.org/open?pubNo=lrr-2006-6&pa... Retrieved 2007-01-08.
45. Staff. "Type Ia Supernova Progenitors". Swinburne University. http://cosmos.swin.edu.au/entries/typeiasupernovaprogenitors... Retrieved 2007-05-20.
46. Macri, L. M. et al. (2006). "A New Cepheid Distance to the Maser-Host Galaxy NGC 4258 and Its Implications for the Hubble Constant". Astrophysical Journal 652 (2): 1133–1149. doi:10.1086/508530. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006... Retrieved 2007-02-01.
47. Colgate, S. A. (1979). "Supernovae as a standard candle for cosmology". Astrophysical Journal 232 (1): 404–408. doi:10.1086/157300. http://adsabs.harvard.edu/abs/1979ApJ...232..404C. Retrieved 2007-02-01.
48. Howell, D. Andrew; Sullivan, M.; Conley, A.; Carlberg, R. (2007). "Predicted and Observed Evolution in the Mean Properties of Type Ia Supernovae with Redshift". The Astrophysical Journal 667: L37–L40. doi:10.1086/522030. http://adsabs.harvard.edu/abs/2007ApJ...667L..37H. Retrieved 2008-03-19.
49. "Early spectroscopic identification of SN 2008D". Cornell University. 2008. http://adsabs.harvard.edu/abs/2008arXiv0805.1188M. Retrieved 2008-05-22.
50. Naeye, Robert; Gutro, Rob (2008-05-21). "NASA's Swift Satellite Catches First Supernova in the Act of Exploding". NASA/Goddard Space Flight Center. http://www.nasa.gov/centers/goddard/news/topstory/2008/swift... Retrieved 2008-05-22.
51. Pols, Onno (October 26 – November 1, 1995). "Close Binary Progenitors of Type Ib/Ic and IIb/II-L Supernovae". Proceedings of The Third Pacific Rim Conference on Recent Development on Binary Star Research. Chiang Mai, Thailand. pp. 153–158.
52. Ryder, S. D. et al. (2004). "Modulations in the radio light curve of the Type IIb supernova 2001ig: evidence for a Wolf-Rayet binary progenitor?". Monthly Notices of the Royal Astronomical Society 349 (3): 1093–1100. doi:10.1111/j.1365-2966.2004.07589.x. http://adsabs.harvard.edu/abs/2004MNRAS.349.1093R. Retrieved 2007-02-01.
53. Gilmore, Gerry (2004). "The Short Spectacular Life of a Superstar". Science 304 (5697): 1915–1916. doi:10.1126/science.1100370. PMID 15218132. http://www.sciencemag.org/cgi/content/full/sci;304/5679/1915... Retrieved 2007-05-01.
54. a b c d e f Woosley, Stan; Janka, Hans-Thomas (December 2005). "The Physics of Core-Collapse Supernovae" (PDF). Nature Physics 1 (3): 147–154. doi:10.1038/nphys172. http://arxiv.org/pdf/astro-ph/0601261.
55. Richmond, Michael. "Late stages of evolution for low-mass stars". Rochester Institute of Technology. http://spiff.rit.edu/classes/phys230/lectures/planneb/planne... Retrieved 2006-08-04.
56. a b Hinshaw, Gary (2006-08-23). "The Life and Death of Stars". NASA Wilkinson Microwave Anisotropy Probe (WMAP) Mission. http://map.gsfc.nasa.gov/m_uni/uni_101stars.html. Retrieved 2006-09-01.
57. Fewell, M. P. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of Physics 63 (7): 653–658. doi:10.1119/1.17828. http://adsabs.harvard.edu/abs/1995AmJPh..63..653F. Retrieved 2007-02-01.
58. Fleurot, Fabrice. "Evolution of Massive Stars". Laurentian University. http://nu.phys.laurentian.ca/~fleurot/evolution/. Retrieved 2007-08-13.
59. a b Fryer, C. L.; New, K. C. B. (2006-01-24). "Gravitational Waves from Gravitational Collapse". Max Planck Institute for Gravitational Physics. http://relativity.livingreviews.org/Articles/lrr-2003-2/. Retrieved 2006-12-14.
60. Mann, Alfred K.] (1997). Shadow of a star: The neutrino story of Supernova 1987A. New York: W. H. Freeman. pp. 122. ISBN 0716730979. http://www.whfreeman.com/GeneralReaders/book.asp?disc=TRAD&i...
61. Gribbin, John R.; Gribbin, Mary (2000). Stardust: Supernovae and Life - The Cosmic Connection. New Haven: Yale University Press. pp. 173. ISBN 9780300090970. http://yalepress.yale.edu/yupbooks/book.asp?isbn=97803000909...
62. Barwick, S.; Beacom, J. et al. (2004-10-29). "APS Neutrino Study: Report of the Neutrino Astrophysics and Cosmology Working Group" (PDF). American Physical Society. http://www.aps.org/policy/reports/multidivisional/neutrino/u... Retrieved 2006-12-12.
63. Hayakawa, T. et al. (2006). "Principle of Universality of Gamma-Process Nucleosynthesis in Core-Collapse Supernova Explosions". The Astrophysical Journal 648: L47–L50. doi:10.1086/507703.
64. S. Myra, Eric; Burrows, Adam (1990). "Neutrinos from type II supernovae- The first 100 milliseconds". Astrophysical Journal 364: 222–231. doi:10.1086/169405. http://adsabs.harvard.edu/abs/1990ApJ...364..222M.
65. Fryer, C. L.; New, K. B. C. (2006-01-24). "Gravitational Waves from Gravitational Collapse, section 3.1". Los Alamos National Laboratory. http://relativity.livingreviews.org/open?pubNo=lrr-2003-2&pa... Retrieved 2006-12-09.
66. Chris L., Michael (2003). "Black Hole Formation from Stellar Collapse". Classical and Quantum Gravity 20 (10): S73–S80. doi:10.1088/0264-9381/20/10/309. http://adsabs.harvard.edu/abs/2003CQGra..20S..73F. Retrieved 2007-02-01.
67. "Cosmological Gamma-Ray Bursts and Hypernovae Conclusively Linked". European Organisation for Astronomical Research in the Southern Hemisphere (ESO). 2003-06-18. http://www.eso.org/outreach/press-rel/pr-2003/pr-16-03.html. Retrieved 2006-10-30.
68. Fryer, Chris L. (1999). "Mass Limits For Black Hole Formation". The Astrophysical Journal 522 (1): 413–418. doi:10.1086/307647. http://adsabs.harvard.edu/abs/1999ApJ...522..413F. Retrieved 2007-02-01.
69. Boen, Brooke (2007-05-05). "NASA's Chandra Sees Brightest Supernova Ever". NASA. http://www.nasa.gov/mission_pages/chandra/news/chandra_brigh... Retrieved 2007-08-09.
70. Sanders, Robert (2007-05-07). "Largest, brightest supernova ever seen may be long-sought pair-instability supernova". University of California, Berkeley. http://hubblesite.org/newscenter/newsdesk/archive/releases/1... Retrieved 2006-05-24.
71. "Type II Supernova Light Curves". Swinburne University of Technology. http://cosmos.swin.edu.au/lookup.html?e=typeiisupernovalight... Retrieved 2007-03-17.
72. Pastorello, A. et al. (2002). "The type IIn supernova 1995G: interaction with the circumstellar medium". Monthly Notices of the Royal Astronomical Society 333 (1): 27–38. doi:10.1046/j.1365-8711.2002.05366.x. http://adsabs.harvard.edu/abs/2002MNRAS.333...27P. Retrieved 2007-02-01.
73. Utrobin, V. P. (1996). "Nonthermal ionization and excitation in Type IIb supernova 1993J". Astronomy and Astrophysics 306: 219–231. http://adsabs.harvard.edu/abs/1996A&A...306..219U. Retrieved 2007-02-01.
74. Richardson, Dean; Branch, David; Casebeer, Darrin; Millard, Jennifer; Thomas, R. C.; Baron, E. (February 2002). "A Comparative Study of the Absolute Magnitude Distributions of Supernovae". The Astronomical Journal 123 (2): 745–752. doi:10.1086/338318.
75. P. Hoflich, P. Kumar, J. C. Wheeler, ed (2004). "Neutron star kicks and supernova asymmetry". Cosmic explosions in three dimensions: asymmetries in supernovae and gamma-ray bursts. Cambridge: Cambridge University Press. pp. 276. http://adsabs.harvard.edu/abs/2004cetd.conf..276L. Retrieved 2007-02-01.
76. Beasley, D.; Roy, S.; Watzke, M.; Villard, R. (2002-09-19). "Space Movie Reveals Shocking Secrets of the Crab Pulsar". NASA. http://hubblesite.org/newscenter/archive/releases/2002/24/te... Retrieved 2006-08-10.
77. Frail, D. A.; Giacani, E. B.; Goss, W. M.; Dubner, G. (1996). "The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44". The Astrophysical Journal 464 (2): L165–L168. doi:10.1086/310103. http://adsabs.harvard.edu/abs/1996ApJ...464L.165F. Retrieved 2007-02-01.
78. Fryer, Chris L. (2004). "Neutron Star Kicks from Asymmetric Collapse". The Astrophysical Journal 601 (2): L175–L178. doi:10.1086/382044. http://adsabs.harvard.edu/abs/2004ApJ...601L.175F. Retrieved 2007-02-01.
79. "Jets, Not Neutrinos, May Cause Supernova Explosions, Scientists Say". McDonald Observatory. 2002-03-02. http://mcdonaldobservatory.org/news/releases/2000/0302a.html... Retrieved 2006-12-11.
80. Foust, Jeff (2000-01-09). "Evidence presented for new supernova explosion model". Spaceflight Now. http://spaceflightnow.com/news/n0101/09supernova/. Retrieved 2006-12-13.
81. "The VLT Measures the Shape of a Type Ia Supernova". European Organisation for Astronomical Research in the Southern Hemisphere (ESO). 2003-08-06. http://www.eso.org/outreach/press-rel/pr-2003/pr-23-03.html. Retrieved 2006-12-11.
82. Leibundgut, B. (August 29 – September 12, 1993). "Observations of Supernovae". Proceedings of the NATO Advanced Study Institute on the Lives of the Neutron Stars. Kemer, Turkey: Kluwer Academic. pp. 3. ISBN 0-7923-324-6-6.
83. Matz, S. M.; Share, G. H. (1990). "A limit on the production of Ni-56 in a type I supernova". Astrophysical Journal 362: 235–24. doi:10.1086/169259. http://adsabs.harvard.edu/abs/1990ApJ...362..235M. Retrieved 2007-02-01.
84. Schlegel, E. M.; Kirshner, R. P. (1989). "The type Ib supernova 1984L in NGC 991". Astrophysical Journal 98: 577–589. doi:10.1086/115158. http://adsabs.harvard.edu/abs/1989AJ.....98..577S. Retrieved 2007-02-01.
85. Qian, Y.-Z.; Vogel, P.; Wasserburg, G. J. (1998). "Diverse Supernova Sources for the r-Process". The Astrophysical Journal 494 (1): 285–296. doi:10.1086/305198. http://adsabs.harvard.edu/abs/1998ApJ...494..285Q. Retrieved 2007-02-01.
86. Gonzalez, G.; Brownlee, D.; Ward, P. (2001). "The Galactic Habitable Zone: Galactic Chemical Evolution" (PDF). Icarus 152: 185–200. doi:10.1006/icar.2001.6617. http://isotope.colorado.edu/~astr5835/Gonzalez%20et%20al.%20... Retrieved 2007-02-01.
87. "Introduction to Supernova Remnants". High Energy Astrophysics Science Archive Research Center, NASA (HEASARC). 2006-09-07. http://heasarc.gsfc.nasa.gov/docs/objects/snrs/snrstext.html... Retrieved 2006-10-20.
88. Kulyk, Christine L. (2006-06-19). "Explosive Debate: Supernova Dust Lost and Found". space.com. http://www.space.com/scienceastronomy/060619_mystery_monday.... Retrieved 2006-12-01.
89. Preibisch, T.; Zinnecker, H. (2001). "Triggered Star Formation in the Scorpius-Centaurus OB Association (Sco OB2)". ASP Conference Proceedings, From Darkness to Light: Origin and Evolution of Young Stellar Clusters. 243. San Francisco: Astronomical Society of the Pacific. p. 791. Bibcode: 2001ASPC..243..791P.
90. Taylor, G. Jeffrey (2003-05-21). "Triggering the Formation of the Solar System". Planetary Science Research. http://www.psrd.hawaii.edu/May03/SolarSystemTrigger.html. Retrieved 2006-10-20.
91. Melott, A. et al. (2004). "Did a gamma-ray burst initiate the late Ordovician mass extinction?". International Journal of Astrobiology 3 (2): 55–61. doi:10.1017/S1473550404001910. http://arxiv.org/abs/astro-ph/0309415. Retrieved 2007-02-01.
92. "Researchers Detect 'Near Miss' Supernova Explosion". University of Illinois College of Liberal Arts and Sciences. Fall/Winter 2005–2006. pp. 17. http://www.las.uiuc.edu/alumni/news/fall2005/05fall_supernov... Retrieved 2007-02-01.
93. Knie, K. et al. (2004). "60Fe Anomaly in a Deep-Sea Manganese Crust and Implications for a Nearby Supernova Source". Physical Review Letters 93 (17): 171103–171106. doi:10.1103/PhysRevLett.93.171103.
94. Fields, B. D.; Ellis, J. (1999). "On Deep-Ocean Fe-60 as a Fossil of a Near-Earth Supernova". New Astronomy 4: 419–430. doi:10.1016/S1384-1076(99)00034-2. http://arxiv.org/abs/astro-ph/9811457. Retrieved 2007-02-01.
95. Richmond, Michael (2005-04-08). "Will a Nearby Supernova Endanger Life on Earth?" (TXT). http://www.tass-survey.org/richmond/answers/snrisks.txt. Retrieved 2006-03-30. —see section 4.
96. Gorelick, Mark (March 2007). "The Supernova Menace". Sky & Telescope.
97. Gehrels, Neil; Laird, Claude M. et al. (2003-03-10). "Ozone Depletion from Nearby Supernovae". Astrophysical Journal 585: 1169–1176. doi:10.1086/346127. http://xxx.lanl.gov/abs/astro-ph/0211361. Retrieved 2007-02-01.
98. van der Sluys, Marc; Lamers, H. J. G. L. M. (2003). "The dynamics of the Wolf-Rayet ring nebula M1-67". Astronomical Institute, Utrecht. http://www.astro.uu.nl/~sluys/m1-67/. Retrieved 2007-06-07.
99. Staff (2003-01-31). "The William Herschel telescope finds the best candidate for a supernova explosion". Particle Physics and Astronomy Research Council. http://www.ing.iac.es/PR/press/ing12003.html. Retrieved 2007-01-05.
100. van Boekel, R.; Schöller, M.; Herbst, T. (2003-11-18). "Biggest Star in Our Galaxy Sits within a Rugby-Ball Shaped Cocoon". European Organisation for Astronomical Research in the Southern Hemisphere (ESO). http://www.eso.org/outreach/press-rel/pr-2003/pr-31-03.html. Retrieved 2007-01-08.
101. Milan, Wil (2000-03-07). "Possible Hypernova Could Affect Earth". space.com. http://www.space.com/scienceastronomy/astronomy/milan_eta_ca... Retrieved 2007-01-06.
102. Than, Ker (2006-07-19). "Mystery of Explosive Star Solved". space.com. http://www.space.com/scienceastronomy/060719_ophiuchi_nova.h... Retrieved 2007-01-08.
103. Staff (2006-07-25). "Astronomers See Future Supernova Developing". SpaceDaily. http://www.spacedaily.com/reports/Astronomers_See_Future_Sup... Retrieved 2006-12-01.
104. Thoroughgood, T. D.; Dhillon, V. S.; Littlefair, S. P.; Marsh, T. R.; Smith, D. A. (2002). "The recurrent nova U Scorpii -- A type Ia supernova progenitor". The Physics of Cataclysmic Variables and Related Objects. 261. San Francisco, CA: Astronomical Society of the Pacific. Bibcode: 2002ASPC..261...77T.
105. Kanipe, Jeff (2000-08-05). "Skywatch—Watch This Space!". space.com. http://www.space.com/scienceastronomy/astronomy/skywatch_000... Retrieved 2007-01-06.
106. Jura, M.; Velusamy, T.; Werner, M. W. (2001-06-05). "What next for the Likely Pre-Supernova, HD 179821?". American Astronomical Society. http://www.aas.org/publications/baas/v33n2/aas198/66.htm. Retrieved 2007-01-08.
107. Josselin, E.; Lèbre, A. (2001). "Probing the post-AGB nature of HD 179821" ([dead link]). Astronomy and Astrophysics 367: 826–830. doi:10.1051/0004-6361:20000496.
108. Than, Ker (2004-10-04). "Astronomers Demonstrate a Global Internet Telescope". University of Manchester. http://www.jb.man.ac.uk/news/evlbi/. Retrieved 2007-01-08.
109. Weaver, D.; Humphreys, R. (2007-01-08). "Astronomers Map a Hypergiant Star's Massive Outbursts". HubbleSite NewsCenter. http://hubblesite.org/newscenter/archive/releases/2007/03/fu... Retrieved 2007-01-16.
110. "Supernova Remnants and Neutron Stars". Harvard-Smithsonian Center for Astrophysics. 2005-08-02. http://chandra.harvard.edu/resources/faq/sources/snr/snr-5.h... Retrieved 2006-06-08.
111. Kaler, Jim. "Regor". University of Illinois. http://www.astro.uiuc.edu/~kaler/sow/regor.html. Retrieved 2007-01-08.
112. Kaler, Jim (1999-04-09). "WR 104: Pinwheel Star". Astronomy Picture of the Day. http://zuserver2.star.ucl.ac.uk/~apod/apod/ap990409.html. Retrieved 2007-01-08.
113. Lloyd, Robin (2006-09-04). "Strange Space Pinwheels Spotted". space.com. http://www.space.com/scienceastronomy/060904_mystery_monday.... Retrieved 2007-01-08.
114. Landsman, W.; Simon, T.; Bergeron, P. (1999). "The hot white-dwarf companions of HR 1608, HR 8210, and HD 15638". Astronomical Society of the Pacific 105 (690): 841–847. doi:10.1086/133242. http://adsabs.harvard.edu/abs/1993PASP..105..841L. Retrieved 2007-02-01.
115. Samuel, Eugenie (2002-05-23). "Supernova poised to go off near Earth". New Scientist. http://www.newscientist.com/article.ns?id=dn2311. Retrieved 2007-01-12.
116. Tzekova, S. Y. et al. (2004). "IK Pegasi (HR 8210)". ESO. http://www.eso.org/outreach/eduoff/edu-prog/catchastar/CAS20... Retrieved 2007-01-12.