chapter 13: chapter 13: the deaths of stars the helix nebula
TRANSCRIPT
Structure of an Old Low-Mass StarStructure of an Old Low-Mass Star
Near the end of its life, a low-mass star like the Sun travels up the AGB and becomes a supergiant.
Supernovae Proceed IrregularlySupernovae Proceed Irregularly
Computer simulations showing how chaotic the supernova is deep inside the star as it begins to explode.
Rotating, Magnetized Neutron StarRotating, Magnetized Neutron Star
Charged particles are accelerated near a neutron star’s magnetic poles and produce two oppositely directed beams of radiation.
WHAT DO YOU THINK?WHAT DO YOU THINK?
Will the Sun someday stop shining? If so, how?
What is a nova?Where do heavy elements on the Earth
like carbon, silicon, oxygen, iron, and uranium come from?
What are cosmic rays?What is a pulsar?
You will discover…You will discover…
what happens to stars when core helium fusion ceases
how heavy elements are created the characteristics of the end of stellar
evolutionwhy some stars go out relatively gently,
while others go with a bang the incredible densities of neutron stars
and how they are observed
Sirius and White DwarfSirius and White Dwarf
Sirius B, a white dwarf, at the five o’clock position
Both are hot blackbodies and strong emitters of X rays
Nova Herculis 1934Nova Herculis 1934
Shortly after peak brightness as a magnitude –3 star.
Two months later, magnitude +12.
Supernovae Proceed IrregularlySupernovae Proceed Irregularly
Chaos helps account for the lopsided distribution of all elements in this supernova remnant. X-ray images of a supernova remnant taken by Chandra.
Gum NebulaGum Nebula
The Gum Nebula, created by a supernova 11,000 years ago, is the largest known supernova remnant. It now has a diameter of about 2300 ly.
Cassiopeia ACassiopeia A
An X-ray picture of Cassiopeia A taken by Chandra
Radio image produced by the Very Large Array (VLA)
Crab Nebula and PulsarCrab Nebula and Pulsar
Observations at different wavelengths give astronomers information about the nebula’s chemistry, motion, history, and interactions with preexisting gas and dust.
Crab Nebula and PulsarCrab Nebula and Pulsar
The Crab’s visible flashes and X-ray pulses have identical periods of 0.033 seconds.
How Magnetic Field Strengths IncreaseHow Magnetic Field Strengths Increase
As a star collapses, it carries the magnetic field inward, thereby increasing its strength.
Neutron Star’s InteriorNeutron Star’s Interior
The neutron star has a superconducting, superfluid core 9.7 km in radius, surrounded by a 0.6-km-thick mantle of superfluid neutrons. The neutron star’s crust is only 0.3 km thick.
Model of a Pulsating X-RayModel of a Pulsating X-Ray
Infalling gas is funneled down onto the neutron star’s magnetic poles, where it strikes the star with enough energy to create two X-ray–emitting hot spots.
Summary of Stellar EvolutionSummary of Stellar Evolution
The evolution of isolated stars depends on their masses.
WHAT DID YOU THINK?WHAT DID YOU THINK? Will the Sun someday cease to exist? If so, how? The Sun will shed matter as a planetary nebula in about 6 billion years and then cease
nuclear fusion. Its remnant white dwarf will dim over the succeeding billions of years. What is a nova? A nova is a relatively gentle explosion of hydrogen gas on the surface of a white dwarf
in a binary star system. What are the origins of the carbon, silicon, oxygen, iron, uranium, and other heavy
elements on Earth? These elements are created during stellar evolution, by supernovae, and by colliding
neutron stars. What are cosmic rays? Cosmic rays are high-speed particles (mostly hydrogen and other atomic nuclei) in
space. Many of them are believed to have been created as a result of supernovae. What is a pulsar? A pulsar is a rotating neutron star in which the magnetic field’s axis does not coincide
with the rotation axis. The beam of radiation it emits sweeps across our region of space.
Key TermsKey Terms
asymptotic giant branch (AGB) starChandrasekhar limitcosmic raycosmic ray showerglitchhelium shell flashhelium shell fusionlighthouse modelneutron degeneracy pressureneutron star
nova (plural novae)photodisintegrationplanetary nebulapulsarquarksecondary cosmic raysupernovaType Ia supernovaType II supernovawhite dwarfX-ray burster