11.14 Key Terms
Accretion disk: the disk of gas and dust found orbiting newborn stars, as well as compact stellar remnants such as white dwarfs, neutron stars, and black holes when they are in binary systems and are sufficiently close to their binary companions to draw off material. 11.13
Balmer lines: the hydrogen lines in the visible part of the spectrum. 11.2
Black dwarf: a former white dwarf star that has become a cold stellar corpse with the mass of a star and the size of a planet after many billions of years. 11.6
Black hole: a region in spacetime where gravity is so strong that nothing—not even light—can escape. 11.13
Cataclysmic Variables: binary stars which consist of a white dwarf primary and an orbiting secondary star. 11.7
Cepheid Variables: an important class of pulsating variable stars. 11.7
Chandrasekhar limit: the upper limit to the mass of a white dwarf (equals 1.4 times the mass of the Sun). 11.6
Degenerate gas: a gas that resists further compression because no two electrons can be in the same place at the same time doing the same thing (Pauli exclusion principle). 11.6
Diamond-like star: a degenerate (white dwarf) star that cools down to the point where the atoms inside it in essence “solidify” into a giant, highly compact lattice (organized rows of atoms, just like in a crystal). 11.6
Dwarf stars: stars with radii equal to, or less than, that of the Sun. 11.3
Event horizon: a boundary in spacetime such that events inside the boundary can have no effect on the world outside it—that is, the boundary of the region around a black hole where the curvature of spacetime no longer provides any way out. 11.13
General theory of relativity: Einstein’s theory relating gravity and the structure (geometry) of space and time. 11.13
Giant stars: stars with radii between 10 and 100 times that of the Sun. 11.3
Hertzsprung–Russell (H–R) diagram: diagram that summarizes the relationship between the luminosity and surface temperature of stars. 11.4
High-mass star: any star with mass exceeding four times that of the Sun. 11.3
Ia supernovae: a white dwarf explosion where the white dwarf is completely destroyed, leaving behind no remnant. 11.8
Initial mass: the mass a star possesses at the beginning of its lifetime before it begins to lose mass in the process of aging and dying. 11.5
Intermediate-mass stars: stars with a mass between 1.33 and 4 times the mass of the Sun. 11.3
Low-mass stars: the Sun, as well as all other stars with a mass less than 1.33 times the mass of the Sun. 11.3
Neutrino: ghostly subatomic particles that carry away some of the nuclear energy when an electron and a proton in the star’s core merge to make a neutron. 11.10
Neutron star: a compact object of extremely high density composed almost entirely of neutrons. 11.10
Novae: original name used for cataclysmic variables as the star seemingly appeared out of nowhere. 11.7
Nucleosynthesis: the building up of heavy elements from lighter ones by nuclear fusion. 11.9
Pulsar: a variable radio source of small physical size that emits very rapid radio pulses in very regular periods that range from fractions of a second to several seconds; now understood to be a rotating, magnetic neutron star that is energetic enough to produce a detectable beam of radiation and particles. 11.12
Pulsating Variables: stars that swell and shrink, which affects the star’s brightness. 11.7
Schwarzschild radius: the radius of the event horizon. 11.13
Singularity: the point of zero volume and infinite density to which any object that becomes a black hole must collapse, according to the theory of general relativity. 11.13
Spaghettification: the process of stretching and narrowing that occurs due to the force of gravity that a singularity exerts. 11.13
Spectral class: the classification of stars according to their temperatures using the characteristics of their spectra; the types are O, B, A, F, G, K, and M with L, T, and Y added recently for cooler star-like objects that recent survey have revealed. 11.2
Supergiant stars: stars with radii more than 100 times than that of the Sun. 11.3
Supernova: an explosion when an enormous amount of fusion (especially of carbon) takes place all at once. 11.8
Triple-alpha process: the process by which three helium atoms can begin to fuse to form a single carbon nucleus once the temperature in a star’s core reaches that of 100 million K (but not before such point). 11.5
Type II supernova: a stellar explosion produced at the endpoint of the evolution of stars whose mass exceeds roughly 10 times the mass of the Sun. 11.10
Variable stars (variables): when a star changes luminosity due to some sort of physical characteristic, not due to an eclipse. 11.7
White dwarf: a star that has achieved a final state of equilibrium after the helium in its core has been exhausted. 11.6
Zero-age: the time when a star stops contracting, settles onto the main sequence, and begins to fuse hydrogen in its core. 11.5
