A supernova is a stellar explosion that is more energetic than a nova. Supernovae (plural) 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 is expected to emit over its entire life span. Several large stars within the Milky Way have been suggested as possible supernovae within the next million years. These include Rho Cassiopeiae, Eta Carinae, RS Ophiuchi, U Scorpii, VY Canis Majoris, Betelgeuse, Antares, and Spica.
The explosion expels much or all of a star's material at a velocity of up to 30,000 kms (10% of 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.
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. The word supernova was coined by Swiss astrophysicist and astronomer Fritz Zwicky, and was first used in print in 1926.
Several types of supernovae exist. Types I and II can 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 generating 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 (either through accretion or 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 solar mass).
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 9 solar masses, such as the Sun, evolve into white dwarfs without ever becoming supernovae.
Although no supernova has been observed in the Milky Way since 1604, supernovae remnants indicate on average the event occurs about once every 50 years in 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.
Hipparchus' interest in the fixed stars may have been inspired by the observation of a supernova (according to Pliny).
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 Islamic astronomers.
The widely observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the latest 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.
Johannes Kepler began observing SN 1604 on October 17, 1604. It was the second supernova to be observed in a generation (after SN 1572 seen by Tycho Brahe in Cassiopeia).
Since the development of the telescope the field of supernova discovery has extended 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. American astronomers Rudolph Minkowski and Fritz Zwicky developed the modern supernova classification scheme beginning in 1941.
In the 1960s astronomers found that the maximum intensities of supernova explosions could be used as standard candles, hence indicators of astronomical distances. Some of the most distant supernovae recently observed appeared dimmer than expected. This supports the view that the expansion of the universe is accelerating.
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 matched the times of 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 professional installations such as the Katzman Automatic Imaging Telescope.
Recently the Supernova Early Warning System (SNEWS) project has 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. Supernova spectroscopy, used to study the physics and environments of supernovae, is more practical at low than at high redshift. Low redshift observations also anchor the low-distance end of the Hubble curve, which is a plot of distance versus redshift for visible galaxies.
A near-Earth supernova is a supernova close enough to the Earth to have noticeable effects on its biosphere. This would need to be nearer than about 100 to 3000 light-years away, depending upon type and energy - different figures have been suggested.
Gamma rays from a supernova would 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 Ordovician-Silurian 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. Iron-60 enrichment was later reported in deep-sea rock of the Pacific Ocean.
In 2009, elevated levels of nitrate ions were found in Antarctic ice, which coincided with the 1006 and 1054 supernovae. Gamma rays from these supernovae could have boosted levels of nitrogen oxides, which became trapped in the ice.
Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because these supernovae arise from dim, common white dwarf stars, it is likely that a supernova that can affect the Earth will occur unpredictably and 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. 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.
Several large stars within the Milky Way have been suggested as possible supernovae within the next million years. These include Rho Cassiopeiae, Eta Carinae, RS Ophiuchi, U Scorpii, 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 31 million kilometres apart. The dwarf has an estimated mass 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.
Music of the Spheres
Astronomers discover new kind of supernova PhysOrg - March 26, 2013
This artist's conception shows the suspected progenitor of a new kind of supernova called Type Iax. Material from a hot, blue helium star at right is funneling toward a carbon/oxygen white dwarf star at left, which is embedded in an accretion disk. In many cases the white dwarf survives the subsequent explosion. Previously, supernovae were divided into either core-collapse or Type Ia categories. Core-collapse supernovae are the explosion of a star about 10 to 100 times as massive as our sun. Type Ia supernovae are the complete disruption of a tiny white dwarf. This new type, Iax, is fainter and less energetic than Type Ia. Although both types come from exploding white dwarfs, Type Iax supernovas may not completely destroy the white dwarf.
Rare Element on Earth Discovered in Ancient Starlight Live Science - February 23, 2012
Light from three ancient stars at the edge of the Milky Way indicates that the stars contain tellurium, a brittle, superconducting element that is rare on Earth. The cosmic discovery, which also spotted traces of other heavy elements, supports the theory that these elements were synthesized in the rapidly collapsing cores of rare supernovas (stellar explosions).
In a Star's Final Days, Astronomers Hunt 'Signal of Impending Doom' Science Daily - December 1, 2011
An otherwise nondescript binary star system in the Whirlpool Galaxy has brought astronomers tantalizingly close to their goal of observing a star just before it goes supernova. In the first survey of its kind, the researchers have been scanning 25 nearby galaxies for stars that brighten and dim in unusual ways, in order to catch a few that are about to meet their end. In the three years since the study began, this particular unnamed binary system in the Whirlpool Galaxy was the first among the stars they've cataloged to produce a supernova.
Small bangs and white holes PhysOrg - May 23, 2011
Gamma-ray bursts. We tend to think of them as big explosions - but it has been suggested that they might actually be Small Bangs. Most gamma-ray bursts come in two flavors. Firstly, there are long duration bursts which form in dense star-forming regions and are associated with supernovae – which would understandably generate a sustained outburst of energy. The technical definition of a long duration gamma-ray burst is one that is more than two seconds in duration – but bursts lasting over a minute are not unusual
Image: Galactic super-volcano in action PhysOrg - August 19, 2010
Supernovae mystery solved PhysOrg - July1, 2010
Supernovae are gigantic stellar explosions that can be seen across the entire universe. Type 'Ia supernovae' are a relatively homogeneous class of stellar explosions, which researchers use as 'standard candles' to observe the acceleration of the universe.
New type of supernova may shed light on some universal mysteries PhysOrg - May 20, 2010
Stellar blast sparks controversy BBC - May 20, 2010
Astronomers have put forward opposing explanations for what could be a new type of exploding star or supernova.
Astronomers discover secret of the supernova Telegraph.co.uk - February 18, 2010
Nasa astronomers may have finally discovered what initially sparks a cosmic explosion, according to new research.
Superbright Supernova Is First of Its Kind Science Daily - December 2, 2009
n extraordinarily bright, extraordinarily long-lasting supernova named SN 2007bi, snagged in a search by a robotic telescope, turns out to be the first example of the kind of stars that first populated the Universe. The superbright supernova occurred in a nearby dwarf galaxy, a kind of galaxy that's common but has been little studied until now, and the unusual supernova could be the first of many such events soon to be discovered.
Rapid supernova could be new class of exploding star PhysOrg - November 5, 2009
New Type of Supernova Discovered National Geographic - November 6, 2009
11-Billion-Year-Old Giant Supernovae Farthest Ever Detected PhysOrg - July 8, 2009
Most Distant Supernovae Found National Geographic - July 8, 2009
First 3-D Fly-Through of a Supernova Remnant National Geographic - January 7, 2009
Ancient supernova mystery solved BBC - December 4, 2008
Supernova "Shock Breakout" Seen From Red Giant For The First Time National Geographic - June 12, 2008
"Light Echo" Helps Solve Supernova Mystery National Geographic - May 29, 2008
Astronomers have used an interstellar "mirror" to solve the longstanding mystery over what kind of supernova created Cassiopeia A, one of the brightest radio objects in the sky. Cass A, as the object is often called, is the expanding remains of a stellar explosion about 9,000 light-years away that is believed to have occurred around A.D. 1680. Until now no one has been able to pinpoint the exact nature of the blast.
Supernova Caught Starting to Explode for First Time National Geographic - May 21, 2008
A brilliant burst of light marking a dying star's final moments before exploding has been glimpsed by astronomers for the first time. Called a shock breakout, the x-ray flash - detected in January - signals the destruction of a star several times more massive than our sun.
Brightest Known Supernova Detected National Geographic - October 15, 2007
Enigmatic supernova smashes brightness record New Scientist - October 12, 2007
Supernova blazed like 100 billion suns MSNBC - October 12, 2007
The Brightest Supernova Ever NASA - May 7, 2007
Astrophysicists Explain Differences In Brightness Of Supernova Explosions Science Daily - February 23, 2007
Brightest supernova discovery hints at stellar collision New Scientist - January 4, 2007
Supernova captured in 'real time' BBC - August 30, 2006
Mystery object found in supernova's heart Space.com - July 7, 2006
... energetic X-ray emissions of the blue point-like object cycles every 6.7 hours tens of thousands of times longer than expected for a freshly created neutron star
Native Americans may have recorded supernova explosion in 1006 AD Space.com - June 6, 2006
Supernova shock wave creates halo effect New Scientist - August 19, 2005
The shock wave from a bright supernova that exploded in 1987 has now reached the edge of a cavity around the dead star, reveal new observations with the Hubble Space Telescope and the Chandra X-ray Observatory.As intense heat from the shock wave continues to spread, it will illuminate the dense gas blown off by the detonating star, which was originally about 20 times more massive than our Sun.Called 1987A, the supernova was the brightest recorded in 400 years and exploded in a nearby galaxy called the Large Magellanic Cloud. Astronomers believe that about a million years before the supernova, the star lost most of its outer layers through a slow-moving wind of particles.
The Last Supernova - 1604: 400-Year-Old Explosion Imaged - Space.com - October 2004
Hubble Reveals Dramatic New Phase of a Supernova Explosion Space.com - February 2004
A shock wave from an exploding star known as Supernova 1987A lights up spots in a surrounding ring of dust and gas, in the latest snapshot from the Hubble Space Telescope. It's the most dramatic stellar explosion witnessed in centuries - New images from the Hubble Space Telescope show the dying star's "ring of fire" entering a new phase of brightness
Hubble looks at dark Universe BBC - April 2003
Astronomers using the Hubble Space Telescope have found two distant supernovae - exploding stars - that provide new clues about the accelerating Universe and its mysterious "dark energy".
Astronomers predict stellar explosion for the first time BBC - April 2003
The star in question is designated Supernova 2003dh and was seen to brighten on 8 April. The prediction was the consequence of detecting a pulse of energy in the form of gamma rays from the same direction 10 days earlier. Before this observation, and the prompt given to them by the gamma-ray burst, scientists could not predict the explosion of a supernova to an accuracy of better than a few million years.
Hubble looks at dark Universe BBC - April 2003
Astronomers using the Hubble Space Telescope have found two distant supernovae - exploding stars - that provide new clues about the accelerating Universe and its mysterious "dark energy". The supernovae are approximately 4.7 and 7.6 billion light-years from Earth, deep in the constellation of Ursa Major, the Great Bear. Two views of the same patch of sky taken several years apart revealed the supernovae, among the most distant ever seen and certainly the most detailed.
Astronomers Discover "Bulls-Eye" Pulsar In Supernova Remnant June 2002 - Science Daily
Astronomers from the University of Massachusetts and Columbia University have found the “bulls-eye” pulsar in a bright ring of high-energy particles in a distant supernova remnant. This discovery, made with NASA’s Chandra X-ray Observatory and the Arecibo Radio Telescope, will help scientists better understand how neutron stars channel enormous amounts of energy into particles moving near the speed of light. Chandra’s image of the supernova remnant SNR G54.1+0.3 reveals a bright, point-like central source, which is surrounded by a ring and two jet-like structures in an extended nebula of high-energy particles. The radio data show that this bright central source is a neutron star, or pulsar, that is rotating 7 times per second.
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