Supernova Explosions
Δημοσιεύθηκε στις 11 Δεκ 2013
A look at the sensational death of
stars in supernova explosions which shine as bright as a 100 billion
suns and release jets of high-energy matter as gamma-ray bursts and
x-ray radiation. Also a look at supernovas recorded throughout history
and how stardust creates the building blocks of planets and life.
A
supernova (abbreviated SN, plural SNe after "supernovae") is a stellar
explosion that is more energetic than a nova. It is pronounced
/ˌsuːpəˈnoʊvə/ with the plural supernovae /ˌsuːpəˈnoʊviː/ or supernovas.
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 is expected to emit over its entire
life span. The explosion expels much or all of a star's material at a
velocity of up to 30,000 km/s (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
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 are far less luminous. The word
supernova was coined by Walter Baade and Fritz Zwicky in 1931.
Supernovae
can be triggered in one of two ways: by the sudden reignition of
nuclear fusion in a degenerate star; or by the collapse of the core of a
massive star. A degenerate white dwarf may accumulate sufficient
material from a companion, either through accretion or via a merger, to
raise its core temperature, ignite carbon fusion, and trigger runaway
nuclear fusion, completely disrupting the star. The core of a massive
star may undergo sudden gravitational collapse, releasing gravitational
potential energy that can create a supernova explosion.
Although
no supernova has been observed in the Milky Way since SN 1604,
supernovae remnants indicate that on average the event occurs about
three times every century 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.
Observation history
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.
stars in supernova explosions which shine as bright as a 100 billion
suns and release jets of high-energy matter as gamma-ray bursts and
x-ray radiation. Also a look at supernovas recorded throughout history
and how stardust creates the building blocks of planets and life.
A
supernova (abbreviated SN, plural SNe after "supernovae") is a stellar
explosion that is more energetic than a nova. It is pronounced
/ˌsuːpəˈnoʊvə/ with the plural supernovae /ˌsuːpəˈnoʊviː/ or supernovas.
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 is expected to emit over its entire
life span. The explosion expels much or all of a star's material at a
velocity of up to 30,000 km/s (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
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 are far less luminous. The word
supernova was coined by Walter Baade and Fritz Zwicky in 1931.
Supernovae
can be triggered in one of two ways: by the sudden reignition of
nuclear fusion in a degenerate star; or by the collapse of the core of a
massive star. A degenerate white dwarf may accumulate sufficient
material from a companion, either through accretion or via a merger, to
raise its core temperature, ignite carbon fusion, and trigger runaway
nuclear fusion, completely disrupting the star. The core of a massive
star may undergo sudden gravitational collapse, releasing gravitational
potential energy that can create a supernova explosion.
Although
no supernova has been observed in the Milky Way since SN 1604,
supernovae remnants indicate that on average the event occurs about
three times every century 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.
Observation history
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.
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