Chapter 13

Supernova 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

Structure of an Old High-Mass Star

-hydrogen-fusing shell -helium-fusing shell -carbon-fusing shell -neon fusing shell

Cosmic Ray Shower

-impact between a cosmic ray and an air molecule -which leads to the creation of numerous secondary cosmic rays

Nova Herculis 1934

-shortly after peak brightness as a magnitude -3 star. -two months later, magnitude +12.

Bipolar Planetary Nebula

1. The star ejects a doughnut-shaped cloud of gas and dust from its equator. 2. The star then ejects gas from its entire surface. 3. The doughnut channels the ejected gas into two oppositely directed streams 4.

There is a mass limit for a star in the white-dwarf phase, the Chandrasakhar limit, beyond which the electron- degeneracy pressure can no longer support the star against its own gravity. This mass limit is

14 solar masses

A high mass star near the end of its life undergoes successive cycles of energy generation within its core in which gravitational collapse increases the temperature to the point where a new nuclear fusion cycle generates sufficient energy to stop the collapse. This process does not work beyond the silicon-fusion cycle that produces iron. Why is this?

Fusion of iron nuclei into heavier nuclei requires energy rather than producing excess energy and therefore will not produce the additional gas pressure to halt the collapse.

Structure 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

A planetary nebula is

a gas shell, the atmosphere of a red giant star, slowly expanding away from the core of the star

What is a pulsar

a rapidly rotating neutron star, producing beams of radio energy and occasionally of X-rays and visible light

The Oppenheimer-Volkov limit to the amount of mass in a neutron star before neutron degeneracy pressure is unable to withstand the force of gravity and the neutron star is crushed out of existence into a black hole is

about 3 solar masses

In what manner does an isolated white dwarf generate energy?

an isolated white dwarf does not generate energy

What are cosmic rays

atomic nuclei and other subatomic particles traveling through space at more than 90% of the speed of light

Nuclear fusion reactions of helium produce primarily?

carbon and oxygen nuclei

The source of the beams of electromagnetic radiation emitted by pulsars is

charged particles traveling along the magnetic axes of rotation neutron stars; the particles emit light as they are accelerated

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.

White dwarfs are supported from gravitational collapse by

degenerate-electron pressure

In the process of helium shell fusion in low-mass stars near the end of their lives, the star moves upward and to the right on the asymptotic giant branch of the Hertzsprung- Russell diagram. In this process, the star is

expanding, cooling, and becoming more luminous

What is the source of most of the heavy elements on the Earth and in our own bodies?

explosive nucleosynthesis during supernova explosions of massive stars

What prevents a neutron star from collapsing and becoming a black hole?

gravity in the neutron star is balanced by an outward force due to neutron degeneracy

In a star's evolutionary life, the asymptotic giant branch (AGB)is the?

helium shell fusion phase

Sirius and White dwarf

is a white dwarf, at the five o'clock position -both are hot blackbodies and strong emitters of X rays

During its life, a massive star creates heavier and heavier elements in its core through thermonuclear fusion, leading up to silicon and iron. What is the fate of the iron that is created?

it is torn apart by high-energy photons at the end of the star's life.

The characteristics of interiors of white dwarfs are

mainly carbon and oxygen nuclei supported by electron-degeneracy pressure in a volume about the size of the Earth.

Type II Supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Why is this?

massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen

A black hole is so named because

no light can escape from it due to its powerful gravitational field

As time progresses, the pulsate for most solitary pulsars is

slowing down since rotational energy is being used to generate the pulses

The mechanism that gives rise to the phenomenon of the nova is

the complete disintegration of a massive star due to a runway thermonuclear explosion in the star's interior.

A type II suernova is

the explosion of a massive star silicon fusion has produced a core of iron nuclei

Each successive stage of core nuclear reactions in a massive star lasts for considerably less time than the previous stage. One reason for this is that

the more massive the nuclei, the fewer there are of them to react together