Astrophysics of White Dwarfs, Supernovae, and Neutron Stars

What physical process provides the energy for the ejection of a planetary nebula from a low-mass star?

Helium shell flashes in the helium fusion shell.

How does an isolated white dwarf generate energy?

An isolated white dwarf does not generate energy.

What are the interiors of white dwarf stars mainly composed of?

Mainly carbon and oxygen nuclei supported by electron degeneracy pressure.

What characteristic do all solitary white dwarf stars share?

They have ceased to generate energy by thermonuclear processes or gravitational contraction and are slowly cooling down.

What is the motion of a white dwarf on the Hertzsprung-Russell diagram as it evolves?

It moves from upper left to lower right, with size or radius remaining constant as it cools and becomes less luminous.

What causes the nova phenomenon in a white dwarf star?

Explosive hydrogen fusion on the surface of a white dwarf star after mass transfer from a companion star in a binary system.

What is the Chandrasekhar limit?

The mass limit to the total mass of a white dwarf, beyond which the electron degeneracy pressure will be overcome and the core will collapse.

What is the main observational difference between a Type Ia and a Type II supernova?

Hydrogen lines are prominent in the spectrum of a Type II supernova but absent in that of a Type Ia.

Why is the duration of the oxygen-fusing stage in the core of a massive star shorter than that of the carbon-fusing stage?

Oxygen fusion does not begin until the contracting core has reached a higher temperature than that for carbon fusion.

What happens during thermonuclear fusion processes inside massive stars?

They transform elements such as carbon and oxygen into heavier elements and generate excess energy until iron is produced.

The sequence of thermonuclear fusion processes inside massive stars can transform elements
such as carbon and oxygen into heavier elements and generate excess energy until iron has
been produced. Why is it not possible for fusion reactions to release energy from iron nuclei?

The protons and neutrons in an iron nucleus are so tightly bound that fusing other nuclei with iron absorbs energy rather than releasing it.

What is photodisintegration?

The splitting apart of atomic nuclei by gamma rays.

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

Explosive nucleosynthesis during supernova explosions of massive stars.

What is a pulsar?

A rapidly spinning neutron star.

How are neutron stars believed to be created?

By type II supernovae, i.e., explosions of high-mass stars.

What prevents a neutron star from collapsing into a black hole?

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