elements. Just before it exhausts all sources of energy, a massive star has an iron core surrounded by shells<\/div>\n
of silicon, sulfur, oxygen, neon, carbon, helium, and hydrogen. The fusion of iron requires energy (rather than<\/div>\n
releasing it). If the mass of a star\u2019s iron core exceeds the Chandrasekhar limit (but is less than 3 MSun), the core<\/div>\n
collapses until its density exceeds that of an atomic nucleus, forming a neutron star with a typical diameter of<\/div>\n
20 kilometers. The core rebounds and transfers energy outward, blowing off the outer layers of the star in a<\/div>\n
type II supernova explosion.<\/div>\n
<\/div>\n
23.3 Supernova Observations<\/div>\n
A supernova occurs on average once every 25 to 100 years in the Milky Way Galaxy. Despite the odds, no<\/div>\n
supernova in our Galaxy has been observed from Earth since the invention of the telescope. However, one<\/div>\n
nearby supernova (SN 1987A) has been observed in a neighboring galaxy, the Large Magellanic Cloud. The star<\/div>\n
that evolved to become SN 1987A began its life as a blue supergiant, evolved to become a red supergiant, and<\/div>\n
returned to being a blue supergiant at the time it exploded. Studies of SN 1987A have detected neutrinos from<\/div>\n
the core collapse and confirmed theoretical calculations of what happens during such explosions, including<\/div>\n
the formation of elements beyond iron. Supernovae are a main source of high-energy cosmic rays and can be<\/div>\n
dangerous for any living organisms in nearby star systems.<\/div>\n
<\/div>\n
23.4 Pulsars and the Discovery of Neutron Stars<\/div>\n
At least some supernovae leave behind a highly magnetic, rapidly rotating neutron star, which can be observed<\/div>\n
as a pulsar if its beam of escaping particles and focused radiation is pointing toward us. Pulsars emit rapid<\/div>\n
pulses of radiation at regular intervals; their periods are in the range of 0.001 to 10 seconds. The rotating<\/div>\n
neutron star acts like a lighthouse, sweeping its beam in a circle and giving us a pulse of radiation when the<\/div>\n
beam sweeps over Earth. As pulsars age, they lose energy, their rotations slow, and their periods increase.<\/div>\n
<\/div>\n
23.5 The Evolution of Binary Star Systems<\/div>\n
When a white dwarf or neutron star is a member of a close binary star system, its companion star can transfer<\/div>\n
mass to it. Material falling gradually onto a white dwarf can explode in a sudden burst of fusion and make a<\/div>\n
nova. If material falls rapidly onto a white dwarf, it can push it over the Chandrasekhar limit and cause it to<\/div>\n
explode completely as a type Ia supernova. Another possible mechanism for a type Ia supernova is the merger<\/div>\n
of two white dwarfs. Material falling onto a neutron star can cause powerful bursts of X-ray radiation. Transfer<\/div>\n
of material and angular momentum can speed up the rotation of pulsars until their periods are just a few<\/div>\n
thousandths of a second.<\/div>\n
<\/div>\n
23.6 The Mystery of the Gamma-Ray Bursts<\/div>\n
Gamma-ray bursts last from a fraction of a second to a few minutes. They come from all directions and are now<\/div>\n
known to be associated with very distant objects. The energy is most likely beamed, and, for the ones we can<\/div>\n
detect, Earth lies in the direction of the beam. Long-duration bursts (lasting more than a few seconds) come<\/div>\n
from massive stars with their outer hydrogen layers missing that explode as supernovae. Short-duration bursts<\/div>\n
are believed to be mergers of stellar corpses (neutron stars or black holes).<\/div>\n
<\/div>\n
Chapter 23.pdf <\/div>\n
<\/div>\n
OpenStax_Astronomy_CH23_ImageSlideshow.pdf <\/div>\n
<\/div>\n
SUMMARY<\/div>\n
<\/div>\n
23.1 The Death of Low-Mass Stars<\/div>\n
During the course of their evolution, stars shed their outer layers and lose a significant fraction of their initial<\/div>\n
mass. Stars with masses of 8 MSun or less can lose enough mass to become white dwarfs, which have masses<\/div>\n
less than the Chandrasekhar limit (about 1.4 MSun). The pressure exerted by degenerate electrons keeps white<\/div>\n
dwarfs from contracting to still-smaller diameters. Eventually, white dwarfs cool off to become black dwarfs,<\/div>\n
stellar remnants made mainly of carbon, oxygen, and neon.<\/div>\n
<\/div>\n
23.2 Evolution of Massive Stars: An Explosive Finish<\/div>\n
In a massive star, hydrogen fusion in the core is followed by several other fusion reactions involving heavier<\/div>\n
elements. Just before it exhausts all sources of energy, a massive star has an iron core surrounded by shells<\/div>\n
of silicon, sulfur, oxygen, neon, carbon, helium, and hydrogen. The fusion of iron requires energy (rather than<\/div>\n
releasing it). If the mass of a star\u2019s iron core exceeds the Chandrasekhar limit (but is less than 3 MSun), the core<\/div>\n
collapses until its density exceeds that of an atomic nucleus, forming a neutron star with a typical diameter of<\/div>\n
20 kilometers. The core rebounds and transfers energy outward, blowing off the outer layers of the star in a<\/div>\n
type II supernova explosion.<\/div>\n
<\/div>\n
23.3 Supernova Observations<\/div>\n
A supernova occurs on average once every 25 to 100 years in the Milky Way Galaxy. Despite the odds, no<\/div>\n
supernova in our Galaxy has been observed from Earth since the invention of the telescope. However, one<\/div>\n
nearby supernova (SN 1987A) has been observed in a neighboring galaxy, the Large Magellanic Cloud. The star<\/div>\n
that evolved to become SN 1987A began its life as a blue supergiant, evolved to become a red supergiant, and<\/div>\n
returned to being a blue supergiant at the time it exploded. Studies of SN 1987A have detected neutrinos from<\/div>\n
the core collapse and confirmed theoretical calculations of what happens during such explosions, including<\/div>\n
the formation of elements beyond iron. Supernovae are a main source of high-energy cosmic rays and can be<\/div>\n
dangerous for any living organisms in nearby star systems.<\/div>\n
<\/div>\n
23.4 Pulsars and the Discovery of Neutron Stars<\/div>\n
At least some supernovae leave behind a highly magnetic, rapidly rotating neutron star, which can be observed<\/div>\n
as a pulsar if its beam of escaping particles and focused radiation is pointing toward us. Pulsars emit rapid<\/div>\n
pulses of radiation at regular intervals; their periods are in the range of 0.001 to 10 seconds. The rotating<\/div>\n
neutron star acts like a lighthouse, sweeping its beam in a circle and giving us a pulse of radiation when the<\/div>\n
beam sweeps over Earth. As pulsars age, they lose energy, their rotations slow, and their periods increase.<\/div>\n
<\/div>\n
23.5 The Evolution of Binary Star Systems<\/div>\n
When a white dwarf or neutron star is a member of a close binary star system, its companion star can transfer<\/div>\n
mass to it. Material falling gradually onto a white dwarf can explode in a sudden burst of fusion and make a<\/div>\n
nova. If material falls rapidly onto a white dwarf, it can push it over the Chandrasekhar limit and cause it to<\/div>\n
explode completely as a type Ia supernova. Another possible mechanism for a type Ia supernova is the merger<\/div>\n
of two white dwarfs. Material falling onto a neutron star can cause powerful bursts of X-ray radiation. Transfer<\/div>\n
of material and angular momentum can speed up the rotation of pulsars until their periods are just a few<\/div>\n
thousandths of a second.<\/div>\n
<\/div>\n
23.6 The Mystery of the Gamma-Ray Bursts<\/div>\n
Gamma-ray bursts last from a fraction of a second to a few minutes. They come from all directions and are now<\/div>\n
known to be associated with very distant objects. The energy is most likely beamed, and, for the ones we can<\/div>\n
detect, Earth lies in the direction of the beam. Long-duration bursts (lasting more than a few seconds) come<\/div>\n
from massive stars with their outer hydrogen layers missing that explode as supernovae. Short-duration bursts<\/div>\n
are believed to be mergers of stellar corpses (neutron stars or black holes).<\/div>\n
<\/div>\n
Chapter 23.pdf <\/div>\n
<\/div>\n
OpenStax_Astronomy_CH23_ImageSlideshow.pdf <\/div>\n
<\/div>\n
SUMMARY<\/div>\n
<\/div>\n
23.1 The Death of Low-Mass Stars<\/div>\n
During the course of their evolution, stars shed their outer layers and lose a significant fraction of their initial<\/div>\n
mass. Stars with masses of 8 MSun or less can lose enough mass to become white dwarfs, which have masses<\/div>\n
less than the Chandrasekhar limit (about 1.4 MSun). The pressure exerted by degenerate electrons keeps white<\/div>\n
dwarfs from contracting to still-smaller diameters. Eventually, white dwarfs cool off to become black dwarfs,<\/div>\n
stellar remnants made mainly of carbon, oxygen, and neon.<\/div>\n
<\/div>\n
23.2 Evolution of Massive Stars: An Explosive Finish<\/div>\n
In a massive star, hydrogen fusion in the core is followed by several other fusion reactions involving heavier<\/div>\n
elements. Just before it exhausts all sources of energy, a massive star has an iron core surrounded by shells<\/div>\n
of silicon, sulfur, oxygen, neon, carbon, helium, and hydrogen. The fusion of iron requires energy (rather than<\/div>\n
releasing it). If the mass of a star\u2019s iron core exceeds the Chandrasekhar limit (but is less than 3 MSun), the core<\/div>\n
collapses until its density exceeds that of an atomic nucleus, forming a neutron star with a typical diameter of<\/div>\n
20 kilometers. The core rebounds and transfers energy outward, blowing off the outer layers of the star in a<\/div>\n
type II supernova explosion.<\/div>\n
<\/div>\n
23.3 Supernova Observations<\/div>\n
A supernova occurs on average once every 25 to 100 years in the Milky Way Galaxy. Despite the odds, no<\/div>\n
supernova in our Galaxy has been observed from Earth since the invention of the telescope. However, one<\/div>\n
nearby supernova (SN 1987A) has been observed in a neighboring galaxy, the Large Magellanic Cloud. The star<\/div>\n
that evolved to become SN 1987A began its life as a blue supergiant, evolved to become a red supergiant, and<\/div>\n
returned to being a blue supergiant at the time it exploded. Studies of SN 1987A have detected neutrinos from<\/div>\n
the core collapse and confirmed theoretical calculations of what happens during such explosions, including<\/div>\n
the formation of elements beyond iron. Supernovae are a main source of high-energy cosmic rays and can be<\/div>\n
dangerous for any living organisms in nearby star systems.<\/div>\n
<\/div>\n
23.4 Pulsars and the Discovery of Neutron Stars<\/div>\n
At least some supernovae leave behind a highly magnetic, rapidly rotating neutron star, which can be observed<\/div>\n
as a pulsar if its beam of escaping particles and focused radiation is pointing toward us. Pulsars emit rapid<\/div>\n
pulses of radiation at regular intervals; their periods are in the range of 0.001 to 10 seconds. The rotating<\/div>\n
neutron star acts like a lighthouse, sweeping its beam in a circle and giving us a pulse of radiation when the<\/div>\n
beam sweeps over Earth. As pulsars age, they lose energy, their rotations slow, and their periods increase.<\/div>\n
<\/div>\n
23.5 The Evolution of Binary Star Systems<\/div>\n
When a white dwarf or neutron star is a member of a close binary star system, its companion star can transfer<\/div>\n
mass to it. Material falling gradually onto a white dwarf can explode in a sudden burst of fusion and make a<\/div>\n
nova. If material falls rapidly onto a white dwarf, it can push it over the Chandrasekhar limit and cause it to<\/div>\n
explode completely as a type Ia supernova. Another possible mechanism for a type Ia supernova is the merger<\/div>\n
of two white dwarfs. Material falling onto a neutron star can cause powerful bursts of X-ray radiation. Transfer<\/div>\n
of material and angular momentum can speed up the rotation of pulsars until their periods are just a few<\/div>\n
thousandths of a second.<\/div>\n
<\/div>\n
23.6 The Mystery of the Gamma-Ray Bursts<\/div>\n
Gamma-ray bursts last from a fraction of a second to a few minutes. They come from all directions and are now<\/div>\n
known to be associated with very distant objects. The energy is most likely beamed, and, for the ones we can<\/div>\n
detect, Earth lies in the direction of the beam. Long-duration bursts (lasting more than a few seconds) come<\/div>\n
from massive stars with their outer hydrogen layers missing that explode as supernovae. Short-duration bursts<\/div>\n
are believed to be mergers of stellar corpses (neutron stars or black holes).<\/div>\n
<\/div>\n
Chapter 23.pdf <\/div>\n
<\/div>\n
OpenStax_Astronomy_CH23_ImageSlideshow.pdf <\/div>\n
<\/div>\n
SUMMARY<\/div>\n
<\/div>\n
23.1 The Death of Low-Mass Stars<\/div>\n
During the course of their evolution, stars shed their outer layers and lose a significant fraction of their initial<\/div>\n
mass. Stars with masses of 8 MSun or less can lose enough mass to become white dwarfs, which have masses<\/div>\n
less than the Chandrasekhar limit (about 1.4 MSun). The pressure exerted by degenerate electrons keeps white<\/div>\n
dwarfs from contracting to still-smaller diameters. Eventually, white dwarfs cool off to become black dwarfs,<\/div>\n
stellar remnants made mainly of carbon, oxygen, and neon.<\/div>\n
<\/div>\n
23.2 Evolution of Massive Stars: An Explosive Finish<\/div>\n
In a massive star, hydrogen fusion in the core is followed by several other fusion reactions involving heavier<\/div>\n
elements. Just before it exhausts all sources of energy, a massive star has an iron core surrounded by shells<\/div>\n
of silicon, sulfur, oxygen, neon, carbon, helium, and hydrogen. The fusion of iron requires energy (rather than<\/div>\n
releasing it). If the mass of a star\u2019s iron core exceeds the Chandrasekhar limit (but is less than 3 MSun), the core<\/div>\n
collapses until its density exceeds that of an atomic nucleus, forming a neutron star with a typical diameter of<\/div>\n
20 kilometers. The core rebounds and transfers energy outward, blowing off the outer layers of the star in a<\/div>\n
type II supernova explosion.<\/div>\n
<\/div>\n
23.3 Supernova Observations<\/div>\n
A supernova occurs on average once every 25 to 100 years in the Milky Way Galaxy. Despite the odds, no<\/div>\n
supernova in our Galaxy has been observed from Earth since the invention of the telescope. However, one<\/div>\n
nearby supernova (SN 1987A) has been observed in a neighboring galaxy, the Large Magellanic Cloud. The star<\/div>\n
that evolved to become SN 1987A began its life as a blue supergiant, evolved to become a red supergiant, and<\/div>\n
returned to being a blue supergiant at the time it exploded. Studies of SN 1987A have detected neutrinos from<\/div>\n
the core collapse and confirmed theoretical calculations of what happens during such explosions, including<\/div>\n
the formation of elements beyond iron. Supernovae are a main source of high-energy cosmic rays and can be<\/div>\n
dangerous for any living organisms in nearby star systems.<\/div>\n
<\/div>\n
23.4 Pulsars and the Discovery of Neutron Stars<\/div>\n
At least some supernovae leave behind a highly magnetic, rapidly rotating neutron star, which can be observed<\/div>\n
as a pulsar if its beam of escaping particles and focused radiation is pointing toward us. Pulsars emit rapid<\/div>\n
pulses of radiation at regular intervals; their periods are in the range of 0.001 to 10 seconds. The rotating<\/div>\n
neutron star acts like a lighthouse, sweeping its beam in a circle and giving us a pulse of radiation when the<\/div>\n
beam sweeps over Earth. As pulsars age, they lose energy, their rotations slow, and their periods increase.<\/div>\n
<\/div>\n
23.5 The Evolution of Binary Star Systems<\/div>\n
When a white dwarf or neutron star is a member of a close binary star system, its companion star can transfer<\/div>\n
mass to it. Material falling gradually onto a white dwarf can explode in a sudden burst of fusion and make a<\/div>\n
nova. If material falls rapidly onto a white dwarf, it can push it over the Chandrasekhar limit and cause it to<\/div>\n
explode completely as a type Ia supernova. Another possible mechanism for a type Ia supernova is the merger<\/div>\n
of two white dwarfs. Material falling onto a neutron star can cause powerful bursts of X-ray radiation. Transfer<\/div>\n
of material and angular momentum can speed up the rotation of pulsars until their periods are just a few<\/div>\n
thousandths of a second.<\/div>\n
<\/div>\n
23.6 The Mystery of the Gamma-Ray Bursts<\/div>\n
Gamma-ray bursts last from a fraction of a second to a few minutes. They come from all directions and are now<\/div>\n
known to be associated with very distant objects. The energy is most likely beamed, and, for the ones we can<\/div>\n
detect, Earth lies in the direction of the beam. Long-duration bursts (lasting more than a few seconds) come<\/div>\n
from massive stars with their outer hydrogen layers missing that explode as supernovae. Short-duration bursts<\/div>\n
are believed to be mergers of stellar corpses (neutron stars or black holes).<\/div>\n
<\/div>\n
Chapter 23.pdf <\/div>\n
<\/div>\n
OpenStax_Astronomy_CH23_ImageSlideshow.pdf <\/div>\n
<\/div>\n
SUMMARY<\/div>\n
<\/div>\n
23.1 The Death of Low-Mass Stars<\/div>\n
During the course of their evolution, stars shed their outer layers and lose a significant fraction of their initial<\/div>\n
mass. Stars with masses of 8 MSun or less can lose enough mass to become white dwarfs, which have masses<\/div>\n
less than the Chandrasekhar limit (about 1.4 MSun). The pressure exerted by degenerate electrons keeps white<\/div>\n
dwarfs from contracting to still-smaller diameters. Eventually, white dwarfs cool off to become black dwarfs,<\/div>\n
stellar remnants made mainly of carbon, oxygen, and neon.<\/div>\n
<\/div>\n
23.2 Evolution of Massive Stars: An Explosive Finish<\/div>\n
In a massive star, hydrogen fusion in the core is followed by several other fusion reactions involving heavier<\/div>\n
elements. Just before it exhausts all sources of energy, a massive star has an iron core surrounded by shells<\/div>\n
of silicon, sulfur, oxygen, neon, carbon, helium, and hydrogen. The fusion of iron requires energy (rather than<\/div>\n
releasing it). If the mass of a star\u2019s iron core exceeds the Chandrasekhar limit (but is less than 3 MSun), the core<\/div>\n
collapses until its density exceeds that of an atomic nucleus, forming a neutron star with a typical diameter of<\/div>\n
20 kilometers. The core rebounds and transfers energy outward, blowing off the outer layers of the star in a<\/div>\n
type II supernova explosion.<\/div>\n
<\/div>\n
23.3 Supernova Observations<\/div>\n
A supernova occurs on average once every 25 to 100 years in the Milky Way Galaxy. Despite the odds, no<\/div>\n
supernova in our Galaxy has been observed from Earth since the invention of the telescope. However, one<\/div>\n
nearby supernova (SN 1987A) has been observed in a neighboring galaxy, the Large Magellanic Cloud. The star<\/div>\n
that evolved to become SN 1987A began its life as a blue supergiant, evolved to become a red supergiant, and<\/div>\n
returned to being a blue supergiant at the time it exploded. Studies of SN 1987A have detected neutrinos from<\/div>\n
the core collapse and confirmed theoretical calculations of what happens during such explosions, including<\/div>\n
the formation of elements beyond iron. Supernovae are a main source of high-energy cosmic rays and can be<\/div>\n
dangerous for any living organisms in nearby star systems.<\/div>\n
<\/div>\n
23.4 Pulsars and the Discovery of Neutron Stars<\/div>\n
At least some supernovae leave behind a highly magnetic, rapidly rotating neutron star, which can be observed<\/div>\n
as a pulsar if its beam of escaping particles and focused radiation is pointing toward us. Pulsars emit rapid<\/div>\n
pulses of radiation at regular intervals; their periods are in the range of 0.001 to 10 seconds. The rotating<\/div>\n
neutron star acts like a lighthouse, sweeping its beam in a circle and giving us a pulse of radiation when the<\/div>\n
beam sweeps over Earth. As pulsars age, they lose energy, their rotations slow, and their periods increase.<\/div>\n