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supernova

supernova, a massive star in the latter stages of stellar evolution that suddenly contracts and then explodes, increasing its energy output as much as a billionfold. Supernovas are the principal distributors of heavy elements throughout the universe; all elements heavier than iron are produced in supernovas. Supernovas also are the principal heat source for interstellar matter and may be a source of cosmic rays. Recent discoveries have confirmed an underlying connection between supernovas and gamma-ray bursts (GRBs). Both are associated with the deaths of massive stars and they often happen nearly simultaneously. There is no generally agreed upon model for how a massive star explodes. However, the association with gamma rays has renewed interest in the role played by stellar rotation and magnetic fields.

Distribution of Supernovas

At peak intensity, a supernova can shine as brightly as the entire galaxy in which it occurs. Novas are less spectacular and more common; they increase in brightness only by a few thousand times, and several occur in our galaxy every year. Supernovas can occur in that small percentage of stars having a mass greater than 8 to 10 times the mass of the sun and perhaps in certain binary stars.

More than five supernovas have been observed to have occurred in our galaxy in the last thousand years, including the "guest star" in Taurus described by Chinese astronomers in 1054; Tycho's star in Cassiopeia, observed by Tycho Brahe in 1572; and Kepler's supernova in 1604. In 1885 the first extragalactic supernova was discovered telescopically in the Andromeda Galaxy; some 700 others have been observed since. In 1987 Supernova 1987A appeared in the Large Magellanic Cloud. It was the first supernova visible to the unaided eye since 1604, and its eruption marked the first time that neutrinos were detected on earth from such an event (see neutrino astronomy).

Theoretical Models of Supernovas

Type I Supernovas

In the 1930s Fritz Zwicky, Walter Baade, and Rudolph Minkowski developed several models of supernova events. In a star about to become a Type I supernova, the star's hydrogen is exhausted, and the star's gravity pulling inward overcomes the forces of its thermonuclear fires pushing the material outward. As the core begins to contract, the remaining hydrogen ignites in a shell, swelling the star into a giant and beginning the process of helium burning. Eventually the star is left with a still contracting core of carbon and oxygen. If the star, now a white dwarf, has a nearby stellar companion, it will begin to pull matter from the companion. In many stars the excess matter is blown off periodically as a nova; if it is not, the star continues to get more and more massive until the matter in the core begins to contract again. When the star gets so massive that it passes Chandrasekhar's limit (1.44 times the sun's mass), it collapses very quickly and all of its matter explodes.

Type II Supernovas

Type II supernovas involve massive stars that burn their gases out within a few million years. If the star is massive enough, it will continue to undergo nucleosynthesis after the core has turned to helium and then to carbon. Heavier elements such as phosphorus, aluminum, and sulfur are created in shorter and shorter periods of time until silicon results. It takes less than a day for the silicon to fuse into iron; the iron core gets hotter and hotter and in less than a second the core collapses. Electrons are forced into the nuclei of their atoms, forming neutrons and neutrinos, and the star explodes, throwing as much as 90% of its material into space at speeds exceeding 18,630 mi (30,000 km) per sec. After the supernova explosion, there remains a small, hot neutron star, possibly visible as a pulsar, surrounded by an expanding cloud, such as that seen in the Crab Nebula.

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Supernova

Supernova

As stars age, many use up their fuel and fade away to oblivion. Others, however, go out with a bang as supernovae, releasing energies of up to 1044joulesan amount of energy equivalent to 30 times the power of a typical nuclear bomb. The explosions of low-mass stars can be triggered by the accretion of mass from a companion star in a binary system to create classical, or Type Ia, supernovae. These supernovae show no hydrogen in their spectra . Massive stars, on the other hand, proceed through normal nuclear fusion but then, when their energy supply runs out, there is no outward pressure to hold them up and they rapidly collapse. The core is crushed into a neutron star or black hole, and the outer layers bounce and are then hurled outward into the surroundings at many million kilometers per hour. These are Type Ib and II supernovae. The Type II supernovae still eject some hydrogen from the unprocessed atmosphere of the star. During a supernova explosion, temperatures are so high that all the known elements can be produced by nuclear fusion.

The most recent supernova that was close enough to be seen without a telescope occurred in early 1987 within a nearby galaxy , the Large Magellanic Cloud. Known as 1987A, it is the only supernova for which there is accurate data on the progenitor star before it exploded. It has been a tremendous help in understanding how stars explode and expand.

The rapidly growing surface of the star can brighten by up to 100 billion times. Then, as the material gets diluted, it becomes transparent and the brightness fades on time scales of a few years. The ejecta are still moving rapidly, however, and quickly sweep up surrounding matter to form a shell that slows down as mass gets accumulated, an action similar to that of a snowplow. This is the beginning of the supernova remnant that can be visible for tens of thousands of years. 1987A is starting to show such interaction with its surroundings.

Supernova remnants emit various forms of radiation. The material is moving highly supersonically and creates a shock wave ahead of it. The shock heats the material in the shell to temperatures over 1 million degrees, producing bright X rays . In the presence of interstellar magnetism, shocks also accelerate some electrons to almost the speed of light, to produce strong synchrotron radiation at radio wavelengths . Sometimes, even high-energy gamma rays can be produced. Dense areas can also cool quickly and we observe filaments of cool gas, at about 10,000 degrees, in various spectral lines at optical wavelengths.

In 1054 astronomers in China and New Mexico observed a famous example of the explosion of a massive star. What remains is a large volume of material that, with a lot of imagination, looks like a crab and, hence, is named the Crab Nebula. The object is being stimulated by jets from a rapidly spinning (about thirty times a second) neutron star called a pulsar. In most supernova remnants, this pulsar wind nebula is surrounded by the shell discussed above, but remarkably, no one has yet detected the shell around the Crab Nebula. Oppositely, the young supernova remnant Cassiopeia A has a shell and a neutron star but no pulsar wind nebula. Astronomers hope to explain these and many other mysteries about supernovae and their remnants using more multiwavelength observations with new telescopes.

see also Black Holes (volume 2); Cosmic Rays (volume 2); Galaxies (volume 2); Pulsars (volume 2); Stars (volume 2).

John R. Dickel

Bibliography

Robinson, Leif. "Supernovae, Neutrinos, and Amateur Astronomers." Sky and Telescope 98, no. 2 (1999):31-37.

Wheeler, J. Craig. Cosmic Catastrophes. Cambridge, UK: Cambridge University Press,2000.

Zimmerman, Robert. "Into the Maelstrom." Astronomy 26, no. 11 (1998):44-49.

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Supernova

Supernova

Ancient astronomers assigned the word nova, Latin for "new," to any bright star that suddenly appeared in the sky. They called an extremely bright new star a supernova.

Modern astronomers now know that a supernova, one of the most violent events in the universe, is the massive explosion of a star. Only relatively large stars (those having 1.5 times the mass of our Sun or more) explode in supernovae at the end of their lives. Once a star has used up all its nuclear fuel, it begins to collapse in on itself. During this process, energy is released and the outer layers of the star are pushed out. These layers are large and cool, and the star at this point is considered a red giant. The star continues to expand, however, and soon explodes outward with great force. As a result of the explosion, the star sheds its outer atmospheric layers and shines more brightly than the rest of the stars in the galaxy put together.

What happens next depends on the original mass of the star. Stars up to three times the mass of the Sun end up as densely packed neutron stars or pulsars (rapidly rotating stars that emit varying radio waves at precise intervals). Stars more than three times the mass of the Sun collapse, in theory, to form a black hole (an infinite abyss from which nothing can escape).

Words to Know

Black hole: Remains of a massive star that has burned out its nuclear fuel and collapsed under tremendous gravitational force into a single point of infinite mass and gravity.

Chandrasekhar's limit: Theory that determines whether an exploding supernova will become either a neutron star or a black hole depending on its original mass.

Neutrino: High-energy subatomic particle with no electrical charge and no mass, or such a small mass as to be undetectable.

Neutron star: Extremely dense, neutron-filled remains of a star following a supernova.

Nuclear fusion: Merging of two hydrogen nuclei into one helium nucleus, with a tremendous amount of energy released in the process.

Pulsar: Rapidly spinning, blinking neutron star.

Radio waves: Electromagnetic radiation, or energy emitted in the form of waves or particles.

The formation of a supernova

Astronomers did not know what causes a star to explode in a super nova until the 1939, when Indian-born American astrophysicist Subrahmanyan Chandrasekhar (19101995) pieced together the sequence of events leading up to a supernova. He also calculated a figure for the mass of a star (known as Chandrasekhar's limit) that would determine if it would end up as a neutron star or a black hole.

Various theories have been proposed to explain the reasons a star explodes outward while collapsing inward. One theory is that the explosion is caused by a final burst of uncontrolled nuclear fusion. A more recent theory is that the explosion is due to the ejection of a wave of high-energy subatomic particles called neutrinos (electrically neutral particles in the lepton family). The neutrino theory gained greater acceptance following the 1987 supernova in the Large Magellanic Cloud, our galaxy's closest companion. Just before the supernova came into view, a surge of neutrinos was detected in laboratories around the world. This supernova, called Supernova 1987A, was the first visible to the naked eye since 1604.

[See also Star; White dwarf ]

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supernova

supernova Stellar explosion in which virtually an entire star is disrupted. For a week or so, a supernova may outshine all the other stars in its galaxy. After a couple of years, the supernova expands so much it becomes thin and transparent. For hundreds or thousands of years, the ejected material remains visible as a supernova remnant. A supernova is c.1000 times brighter than a nova.

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supernova

su·per·no·va / ˈsoōpərˌnōvə/ • n. (pl. -no·vae / -ˌnōvē/ or -no·vas ) Astron. a star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.

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Supernova

Supernova ★½ 1999 (PG-13)

This one got stuck on the studio shelf for awhile and didn't improve with age. In fact, director Walter Hill was so incensed over studio re-editing that he removed his name, leaving the pseud. “Thomas Lee” to grace this space mishmash. Nick Vanzant (Spader) is stuck piloting a 22nd-century medical vessel after the captain (Forster) is killed. The craft receives a distress call and makes the mistake of rescuing Karl (Facinelli), an odd duck who proves to be very dangerous. You'll wonder what got left on the cutting-room floor. 91m/C VHS, DVD . James Spader, Angela Bassett, Robin Tunney, Peter Facinelli, Lou Diamond Phillips, Wilson Cruz, Robert Forster; D: Walter Hill; W: David Campbell Wilson; C: Lloyd Ahern II; M: David Williams.

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Supernova

Supernova

Guest stars

Types of supernovae

Why a supernova explodes

Supernova 1987a

Resources

A supernova is the massive explosion of a star, and is one of the most violent events in the universe. For instance, with the sun shining as it does every day, it would take the sun around ten billion years to produce the amount of energy generated from an average super-nova. Nova is the Latin word for new and the word super distinguishes a supernova from a regular nova, which increases in brightness but to a lesser degree and with the use of a different type of explosion.

There are two types of supernovae. A Type I supernova happens when a dead star called a white dwarf accretes so much matter from a companion star that it becomes unstable and explodes. A Type II supernova occurs when a high-mass star runs out of thermonuclear fuel. In this case, the stars core collapses and becomes tremendously hard and rigid. The collapsing outer layers of the star bounce off the core and are flung outward with a burst of energy that can rival the output of an entire galaxy.

Guest stars

In AD 1054, a brilliant new star blazed into view into the constellation of Taurus, the Bull. The Chinese astronomers who observed it called it a guest star, and at its peak brightness they could see it even during the day. Over the following months, it gradually faded and disappeared. When astronomers train their telescopes on the location of the former guest star, they see an angry-looking cloud of gas called the Crab Nebula. Several other guest stars appear in the historical record, usually separated by intervals of a few hundred years. They are therefore quite uncommon. Two appeared in AD 1572 and AD 1604, but after then astronomers would have to wait more than 380 years before the next one.

Studies of the Crab Nebula show that it is expanding, as if the enormous cloud of gas had been flung outward from a central point. Modern stellar evolution theory has provided a reason for this: the guest stars were the final acts in the lives of a massive star. These stars end their lives as supernovae, massive explosions that blast the stars outer layers into space. For a short time they can rival the brightness of a small galaxy; later, like dying pieces of coal in a fire, they fade away

Types of supernovae

A supernova is the explosion of a star. In a single cataclysm, a massive star may blow itself to bits, releasing as much energy, for a brief time, as an entire galaxy. There are two types of supernovae.

A Type I supernova is the explosion and complete destruction of a dead star called a white dwarf. (The sun, after it dies, will become a white dwarf.) If the white dwarf is made of carbon (the end product of the thermonuclear reactions that took place during the stars life), and if it is a member of a binary system, a Type I supernova can potentially occur.

Two important effects contribute to a Type I supernova. First, a white dwarf cannot be more massive than about 1.4 solar masses and remain stable. Second, if the white dwarfs companion star expands to become a red giant, some of its matter may be drawn away and sucked onto the surface of the white dwarf. If one could hover in a spacecraft at a safe distance from such a system, the person would see a giant stream of matter flowing from the large, bloated star to its tiny companion, swirling into an accretion disk, which then trickles onto its surface. A white dwarf that is almost 1.4 solar masses may be pushed over the critical mass limit by the constant influx of material. If this happens, the white dwarf will explode in an instantaneous nuclear reaction that involves all the mass of the star.

The popular image of a massive, supergiant star ending its life in one final, dazzling, swan song is what astronomers classify as a Type II supernova. In a Type II supernova, a massive star runs out of thermonuclear fuel and can no longer sustain itself against the inward pull of its own gravity. In a matter of seconds, the star collapses. The core is crushed into a tiny object called a neutron star, which may be no more than 6 mi (10 km) across. The outer layers collapse as well, but when they encounter the extremely hard, rigid, collapsed core, they bounce off it. An immense cloud of glowing gasrushes outward, and some of the nebulae visible in small telescopes are these dispersed outer layers of stars.

Astronomers can tell the type of a supernova by observing its total brightness as well as its spectrum. Type I supernovae release more energy and therefore have a lower absolute magnitude (about 19 at peak brightness, which is as bright as a small galaxy). Since a Type I supernova is the explosion of a dead star made largely of carbon, there is little evidence in its spectrum for the element hydrogen. Type II supernovae, however, have prominent hydrogen lines in their spectra, for hydrogen is the primary element in the exploding star.

Type I supernovae are useful to astronomers trying to determine the distances to other galaxies, which is a very difficult task. Since all Type I supernovae have about the same absolute brightness, astronomers can calculate how far away a Type I supernova is by measuring its apparent brightness and then calculating how far away it must be to appear that bright. Type I supernovae therefore serve as one of several kinds of distance indicators that help astronomers determine the size of the universe.

Why a supernova explodes

If a Type II supernova is the collapse of a massive star, why does a huge explosion result? Astronomers do not have the answer, partly because of the extreme physical conditions that exist in the temperatures (about a trillion degrees) and pressures in a collapsing stellar core, and partly because everything happens very rapidly. The more rapidly the situation is changing, the more difficult it is to simulate it on a computer.

The usual explanation is that the outer layers bounce off the collapsed core. Try this experiment: hold two superballs, one larger than the other, about 5 ft (1.5 m) off the floor. Hold the smaller superball so that it is on top of and touching the larger one. Drop them simultaneously, so they fall with the little ball just above the big one (this takes some practice). If one does it correctly, the large ball (representing the core) will stop dead on the floor, and the little ball (representing the outer layers) will be flung high in the air. Something akin to this is thought to happen in a supernova. As the core collapses, a shock wave develops as the material gets jammed together. The incredible energy involved blasts the stars outer layers far into space.

Supernova 1987a

Supernovae ought to happen in the Earths galaxy about once every 30 years. Until 1987, however, no bright supernova had been seen since 1604. By no means were humans due for onethat is an all-too-frequent abuse of statisticsbut nevertheless a super-nova did explode on February 23, 1987. (To be precise, that was the date that light from the explosion first reached the Earth; the actual explosion took place

KEY TERMS

Core collapse The sudden collapse of a stars central region when the stars last fuel reserves are exhausted. With no energy being produced to sustain it against its own gravity, the core collapses in a fraction of a second, triggering a supernova explosion.

Type I supernova The explosion of a white dwarf in a binary system. Often the white dwarf, which is the dead remnant of a star originally about as massive as the Sun, has a stream of matter being dumped onto its surface by its companion. The white dwarf may be pushed past the limit of 1.4 solar masses, after which it will become unstable and explode.

Type II supernova The explosion of a massive star that has run out of thermonuclear fuel.

170,000 years earlier.) It was not in the Milky Way galaxy, but in one of the small satellite galaxies orbiting it, the Large Magellanic Cloud, visible in the southern hemisphere. It was a distance of 170,000 light-years from the Earth, and became known as SN 1987A. The star that exploded was a blue supergiant, probably 20 times more massive than the sun, and when it exploded it was visible to the naked eye. Supernova 1987A became one of the most studied events in astronomical history, as observations of the expanding blast revealed numerous exciting results.

As a stars core collapses, the protons and electrons in it are smashed together to form a neutron, and every time such a reaction happens, an evanescent particle called a neutrino is created. The neutrinos travel outward from the core at the speed of light, and they are created in such vast numbers that they carry off most of the energy produced during the supernova. Just before SN 1987A became visible, surges of neutrinos were indeed detected here on the Earth. Since the neutrinos escape from the star before the visible explosion, the timing of the event provided important observational support for the idea that core collapse and the subsequent bounce of infalling outer layers drives some supernova explosions.

There are several stars in the Earths celestial neighborhood that are prime supernova candidates. Betelgeuse, the red supergiant that marks Orions right shoulder, and Antares, the brightest star in Scorpio, are two notable examples.

Resources

BOOKS

Hoflich, Peter, Pawan Kumar, and J. Craig Wheeler, eds. Cosmic Explosions in Three Dimensions: Asymmetries in Supernovae and Gamma-ray Bursts. Cambridge, UK, and New York: Cambridge University Press, 2004. Kirshner, Robert P. The Extravagant Universe: Exploding Stars, Dark Energy, and the Accelerating Cosmos. Princeton, NJ, and Oxford, UK: Princeton University Press, 2004.

Mark, Hans, Maureen Salkin, and Ahmed Yousef, eds. Encyclopedia of Space Science & Technology. New York: John Wiley & Sons, 2001.

Stephenson, Francis Richard. Historical Supernovae and their Remnants. Oxford, UK, and New York: Oxford University Press, 2002.

van Putten, Maurice H.P.M. Gravitational Radiation, Luminous Black Holes, and Gamma-ray Burst Supernovae. Cambridge, UK, and New York: Cambridge University Press, 2005.

Jeffrey C. Hall

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Supernova

Supernova

A supernova is the massive explosion of a star , and is one of the most violent events in the Universe. There are two types of supernovae. A Type I supernova happens when a dead star called a white dwarf accretes so much matter from a companion star that it becomes unstable and explodes. A Type II supernova occurs when a high-mass star runs out of thermonuclear fuel. In this case, the star's core collapses and becomes tremendously hard and rigid. The collapsing outer layers of the star bounce off the core and are flung outward with a burst of energy that can rival the output of an entire galaxy .


Guest stars

In a.d. 1054, a brilliant new star blazed into view into the constellation of Taurus, the Bull. The Chinese astronomers who observed it called it a "guest star," and at its peak brightness they could see it even during the day. Over the following months it gradually faded and disappeared. When we train our telescopes on the location of the former guest star, we see an angry-looking cloud of gas called the Crab Nebula. Several other "guest stars" appear in the historical record, usually separated by intervals of a few hundred years. They are therefore quite uncommon. Two appeared in a.d. 1572 and a.d. 1604, but after then astronomers would have to wait more than 380 years before the next one.

Studies of the Crab Nebula show that it is expanding, as if the enormous cloud of gas had been flung outward from a central point. Modern stellar evolution theory has provided a reason for this: the "guest stars" were the final acts in the lives of a massive star. These stars end their lives as supernovae, massive explosions that blast the stars' outer layers into space . For a short time they can rival the brightness of a small galaxy; later, like a dying coal in a fire, they fade away.


Types of supernovae

A supernova is the explosion of a star. In a single cataclysm, a massive star may blow itself to bits, releasing as much energy, for a brief time, as an entire galaxy. There are two types of supernovae.

A Type I supernova is the explosion and complete destruction of a dead star called a white dwarf. (The Sun , after it dies, will become a white dwarf.) If the white dwarf is made of carbon (the end product of the thermonuclear reactions that took place during the star's life), and if it is a member of a binary system, a Type I supernova can potentially occur.

Two important effects contribute to a Type I supernova. First, a white dwarf cannot be more massive than about 1.4 solar masses and remain stable. Second, if the white dwarf's companion star expands to become a red giant, some of its matter may be drawn away and sucked onto the surface of the white dwarf. If you could hover in a spacecraft at a safe distance from such a system, you would see a giant stream of matter flowing from the large, bloated star to its tiny companion, swirling into an accretion disk which then trickles onto its surface. A white dwarf that is almost 1.4 solar masses may be pushed over the critical mass limit by the constant influx of material. If this happens, the white dwarf will explode in an instantaneous nuclear reaction that involves all the mass of the star.

The popular image of a massive, supergiant star ending its life in one final, dazzling, swan song is what astronomers classify as a Type II supernova. In a Type II supernova, a massive star runs out of thermonuclear fuel and can no longer sustain itself against the inward pull of its own gravity. In a matter of seconds, the star collapses. The core is crushed into a tiny object called a neutron star , which may be no more than 6 mi (10 km) across. The outer layers collapse as well, but when they encounter the extremely hard, rigid, collapsed core, they bounce off it. An immense cloud of glowing gas rushes outward, and some of the nebulae visible in small telescopes are these dispersed outer layers of stars.

Astronomers can tell the type of a supernova by observing its total brightness as well as its spectrum . Type I supernovae release more energy and therefore have a lower absolute magnitude (about -19 at peak brightness, which is as bright as a small galaxy). Since a Type I supernova is the explosion of a dead star made largely of carbon, there is little evidence in its spectrum for the element hydrogen . Type II supernovae, however, have prominent hydrogen lines in their spectra, for hydrogen is the primary element in the exploding star.

Type I supernovae are useful to astronomers trying to determine the distances to other galaxies, which is a very difficult task. Since all Type I supernovae have about the same absolute brightness, astronomers can calculate how far away a Type I supernova is by measuring its apparent brightness and then calculating how far away it must be to appear that bright. Type I supernovae therefore serve as one of several kinds of distance indicators that help us determine the size of the Universe.


Why a supernova explodes

If a Type II supernova is the collapse of a massive star, why does a huge explosion result? We do not have the answer, partly because of the extreme physical conditions that exist in the temperatures (about a trillion degrees) and pressures in a collapsing stellar core, and partly because everything happens very rapidly. The more rapidly the situation is changing, the more difficult it is to simulate it on a computer.

The usual explanation is that the outer layers "bounce" off the collapsed core. Try this experiment: hold two superballs, one larger than the other, about 5 ft (1.5 m) off the floor. Hold the smaller superball so that it is on top of and touching the larger one. Drop them simultaneously, so they fall with the little ball just above the big one (this takes some practice). If you do it right, the large ball (the "core") will stop dead on the floor, and the little ball (the "outer layers") will be flung high in the air. Something akin to this is thought to happen in a supernova. As the core collapses, a shock wave develops as the material gets jammed together. The incredible energy involved blasts the star's outer layers far into space.


Supernova 1987A

Supernovae ought to happen in our galaxy about once every 30 years. Until 1987, however, no bright supernova had been seen since 1604. By no means were we "due for one"—that is an all-too-frequent abuse of statistics—but nevertheless a supernova did explode on February 23, 1987. (To be precise, that was the date that light from the explosion first reached us; the actual explosion took place 170,000 years earlier.) It was not in our galaxy, but in one of the small satellite galaxies orbiting it, the Large Magellanic Cloud, visible in the southern hemisphere. It was a distance of 170,000 light-years from Earth , and became known as SN 1987A. The star that exploded was a blue supergiant, probably 20 times more massive than the Sun, and when it exploded it was visible to the naked eye . Supernova 1987A became one of the most studied events in astronomical history, as observations of the expanding blast revealed numerous exciting results.

As a star's core collapses, the protons and electrons in it are smashed together to form a neutron , and every time such a reaction happens, an evanescent particle called a neutrino is created. The neutrinos travel outward from the core at the speed of light, and they are created in such vast numbers that they carry off most of the energy produced during the supernova. Just before SN 1987A became visible, surges of neutrinos were indeed detected here on Earth. Since the neutrinos escape from the star before the visible explosion, the timing of the event provided important observational support for the idea that core collapse and the subsequent bounce of infalling outer layers drives some supernova explosions.

There are several stars in Earth's celestial neighborhood that are prime supernova candidates. Betelgeuse, the red supergiant that marks Orion's right shoulder, and Antares, the brightest star in Scorpio, are two notable examples.

Resources

books

Mark, Hans, Maureen Salkin, and Ahmed Yousef, eds. Encyclopedia of Space Science & Technology. New York: John Wiley & Sons, 2001.

Seeds, M.A. Horizons: Discovering the Universe. Chap. 10. Wiley, 1991.

periodicals

Filippenko, A. "A Supernova with an Identity Crisis." Sky &Telescope (December 1993): 30.

Naeye, R. "Supernova 1987A Revisited." Sky & Telescope (February 1993): 39.

Thorpe, A. "Giving Birth to Supernovae." Astronomy (December 1992): 47.


Jeffrey C. Hall

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Core collapse

—The sudden collapse of a star's central region when the star's last fuel reserves are exhausted. With no energy being produced to sustain it against its own gravity, the core collapses in a fraction of a second, triggering a supernova explosion.

Type I supernova

—The explosion of a white dwarf in a binary system. Often the white dwarf, which is the dead remnant of a star originally about as massive as the Sun, has a stream of matter being dumped onto its surface by its companion. The white dwarf may be pushed past the limit of 1.4 solar masses, after which it will become unstable and explode.

Type II supernova

—The explosion of a massive star that has run out of thermonuclear fuel.

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"Supernova." The Gale Encyclopedia of Science. . Retrieved September 22, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/supernova-0

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