Chapter 13: The Deaths of Stars

superwind

Extremely rapid outflow of matter from giant and supergiant stars, analogous to the solar wind but with much greater mass loss rate.

planetary nebula

An expanding shell of gas ejected from a star during the latter stages of its evolution.

compact object

A star that has collapsed to form a white dwarf, neutron star, or black hole.

black dwarfs

The end state of a white dwarf that has cooled to low temperature.

Chandrasekhar limit

The maximum mass of a white dwarf, about 1.4 solar masses; a white dwarf of greater mass cannot support itself and will collapse.

Roche lobes

In a system with two bodies orbiting each other, the volume of space dominated by the gravitation of one of the bodies.

Roche surface

In a system with two bodies orbiting each other, the outer boundary of the volume of space dominated by the gravitation of one of the bodies.

Lagrange points

Point of stability in the orbital plane of a binary star system, planet, or moon. One is located 60 degrees ahead and one 60 degrees behind the orbiting bodies; another is located between the orbiting bodies.

inner Lagrange L1 point

The point of gravitational equilibrium between two orbiting stars through which matter can flow from one star to the other.

accretion disk

The whirling disk of gas that forms around a compact object such as a white dwarf, neutron star, or black hole as matter is drawn in.

nova

From the Latin “new,” a sudden brightening of a star, making it appear as a “new” star in the sky; thought to be associated with eruptions on white dwarfs in binary systems.

supernovae

A “new” star appearing in Earth’s sky and lasting for a year or so before fading. Caused by the violent explosion of a star.

supernova remnants

The expanding shell of gas marking the site of a supernova explosion.

Type I supernovae

The violent explosion of a star in which the spectrum contains no hydrogen lines.

Type II supernovae

The explosion of a massive star that develops an iron core and collapses.

type Ia supernova

The explosion of a star caused by the collapse of a white dwarf that has gained mass from its binary companion and exceeds the -Chandrasekhar limit.

carbon deflagration

The process in which the carbon in a white dwarf is completely consumed by nuclear fusion, producing a type Ia supernova explosion.

type Ib supernovae

The explosion of a massive star that develops an iron core and collapses after it has lost its outer layers of hydrogen.

synchrotron radiation

Radiation emitted when high-speed electrons move through a magnetic field.

Why can't the lowest-mass main-sequence stars become giants?

They are not massive enough to fuse helium.

What evidence can you give that stars lose mass? Cite at least three observations.

supernovae, planetary nebulae, nova explosions

As a white dwarf cools, it moves toward the lower right in the H-R diagram, maintaining a constant radius. Why doesn't it contract as it cools?

Degenerate matter cannot contract.

Why haven't white dwarfs already cooled to black dwarfs in our Galaxy?

There has not been enough time for these objects to form.

How can white dwarfs be both very hot and have very low luminosity?

They have small surface area.

Why can a nova repeat whereas a supernova cannot repeat? (Select all that apply.)

• As long as more mass is transferred, a nova explosion can occur again.

• In a supernova, the star is ripped apart.

• The core of the star collapses in a supernova.

What processes produce type I supernovae? (Select all that apply.)

• core collapse of a white dwarf

• massive star loses its outer envelope of hydrogen

What processes produce type II supernovae?

collapse of a massive star's iron core

Which of the following is true of a volume of space outlined by a Roche lobe?

It is controlled by a star's gravity.

If the stars in a binary system are far apart, which of the following is true of the Roche lobes?

They are larger than their stars.

Which of the following is true of the inner Lagrange point?

• It is where the Roche lobes touch.

• It is always located between the two stars.

• It is the point through which binary stars can transfer matter.

Matter flowing into a star must do which of the following?

form an accretion disk

In different circumstances, matter flowing into an accretion disk can do which of the following?

• trigger a nova explosion

• fall into the star

• emit x-rays

Which of the following is true of Roche lobes in a binary system?

They enclose the region controlled by each star's gravity.