Chapter 13:Chapter 13:The Deaths

of Stars

The Helix Nebula

Planetary NebulaePlanetary Nebulae

NGC 7293, Helix Nebula

NGC 6826 Menzel 3

From Supergiants to White DwarfsFrom Supergiants to White Dwarfs

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.

Structure of an Old High-Mass StarStructure of an Old High-Mass Star

Supernovae Proceed IrregularlySupernovae Proceed Irregularly

Computer simulations showing how chaotic the supernova is deep inside the star as it begins to explode.

Supernova 1987ASupernova 1987A

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

Post–Main-Sequence Evolution ofPost–Main-Sequence Evolution ofLow-Mass StarsLow-Mass Stars

Bipolar Planetary NebulaBipolar Planetary Nebula

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.

Nova Cygni 1975Nova Cygni 1975

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)

Cosmic Ray ShowerCosmic Ray Shower

Shells of Gas Around SN 1987AShells of Gas Around SN 1987A

Supernova Light CurvesSupernova Light Curves

Recording a PulsarRecording a Pulsar

PSR 0329+54

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.

Glitch & the Vela Pulsar’s Glitch & the Vela Pulsar’s Spindown RateSpindown Rate

Double PulsarDouble Pulsar

Artist’s conception of PSR J0737-3039

X-Ray Pulses from Centaurus X-3X-Ray Pulses from Centaurus X-3

X ray intensity as detected by Uhuru

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.

X Rays from an X-Ray BursterX Rays from an X-Ray Burster

Summary of Stellar EvolutionSummary of Stellar Evolution

The evolution of isolated stars depends on their masses.

Summary of Stellar EvolutionSummary of Stellar Evolution

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