Compact Objects: White Dwarfs, Neutron Stars, and Black Holes

Compact Objects: An Overview

White Dwarfs

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 Lobe: The volume of space a star controls gravitationally within a binary system.

Neutron Stars

Angular Momentum: A measure of the tendency of a rotating body to continue rotating. Mathematically, the product of mass, velocity, and radius.

Accretion Disk: The rotating disk that forms in some situations as matter is drawn gravitationally toward a central body.

Type I Supernova: A supernova explosion caused by the collapse of a white dwarf.

Type II Supernova: A supernova explosion caused by the collapse of a massive star.

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

Supernova Remnant: The expanding shell of gas and dust marking the site of a supernova explosion.

Neutron Star: A small, highly dense star, with a radius of about 10 km, composed almost entirely of tightly packed neutrons.

Pulsar: A source of short, precisely timed radio bursts, understood to be a spinning neutron star.

Lighthouse Model: The explanation of a pulsar as a spinning neutron star sweeping beams of electromagnetic radiation around the sky.

Black Holes

General Theory of Relativity: Einstein’s theory that describes gravity as due to the curvature of spacetime.

Gravitational Radiation: Expanding waves in a gravitational field that transport energy through space at the speed of light, as predicted by general relativity.

Millisecond Pulsar: A pulsar with a pulse period of only a few milliseconds.

Singularity: An object of zero radius and infinite density.

Black Hole: A mass that has collapsed to such a small volume that its gravity prevents the escape of all radiation. Also, the volume of space from which radiation may not escape.

Event Horizon: The boundary of the region of a black hole from which no radiation may escape. No event that occurs within the event horizon is visible to a distant observer.

Schwarzschild Radius: The radius of the event horizon around a black hole.

Time Dilation: The slowing of moving clocks or clocks in strong gravitational fields.

Gravitational Redshift: The lengthening of the wavelength of a photon as it escapes from a gravitational field.

Gamma-Ray Bursts and Hypernovae

Gamma-Ray Burst: A sudden, powerful burst of gamma rays.

Hypernova: Produced when a very massive star collapses into a black hole. Thought to be a possible source of gamma-ray bursts.