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Beyond the Stars Chapters 5-8


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Spectral Type
A classification of the spectrum of a star according to which lines are prominent. A star's spectral type is related to the surface temperature and gravity of the star
Main Sequence
The diagonal band in a color-magnitude or temperature luminosity diagram where most stars are found. It represents the locus of temperature and luminosity that characterizes stars of different mass during the most stable and long-lasting part of their lives.
Metal Rich
Similar to the sun in terms of heavy element abundance
Metal Poor
Lacking in heavy elements compared to the sun.
Population I and II
The two main types of stars in our Galaxy. Population I stars are young, and population II stars are old.
(Color-magnitude diagram) A graphical plotting of colors and magnitudes of stars in a cluster or galaxy from which various characteristics of the stellar population can be inferred.
(Hertzsprung-Russell Diagram) A plot of stellar luminosity (or absolute magnitude) versus effective temperature (or color). Hydrogen-burning stars define a locus (main sequence) in this diagram, which is used to study stellar evolution.
Taking small elements, breaking down to get energy. Occurs in stars because they are made of hydrogen and helium.
T Tauri
Luminous variable stars with low effective temperatures and strong emission lines. These are associated with interstellar gas clouds and found in very young clusters.
A star that has not yet reached its equilibrium state on the main sequence.
Taking big elements, breaking down to get energy.
Describe a typical main sequence star
Middle is hydrogen burning, hydrogen burns out then when helium burns out a red giant forms, then old red giant, the core eventually shrinks and the outer layer is forced out. A planetary nebula forms with a white dwarf in the middle.
Formation of stars
Large gad clouds fragment as they collapse...Dense fragments collapse fastest...outflow and inflow makes stars form (mass determines development)...fusion begins, and a star is born!
A large collection of stars and other material components that are gravitationally bound, and usually separated from neighbors by millions of light-years.
Globular cluster
A usually massive, compact group of starts that are gravitationally stable.
Lines (contours) of constant brightness, as on a map of a galaxy.
Density wave
A periodic dynamical disturbance in the disk of a spiral galaxy in the form of two or more spiral wavefronts of enhanced density and gravity that can self propagate around the disk and so generate the grand design spiral structure that is observed in some spiral galaxies
Missing Mass
Masses derived from looking at galaxies.
Rotation Curve
A plot of the velocity of rotation against the distance from the center.
Velocity Dispersion
The range in velocities seen for example in the stars occupying the center of a galaxy.
Mass to light Ratio
The ratio of the mass of an object to its luminosity, usually expressed in solar units.
Hubble Tuning Fork with types of galaxies
EO (Circle elliptical) E3 (oval shaped elliptical) E7 (Eye shaped elliptical) SO (Irregular) TOP- Sa (spiral with medium nucleus) Sb (spiral with large nucleus) Sc (spiral with small nucleus) BOTTOM- SBa (small barred) SBb (barred spiral) SBc (backwards "S" barred spiral)
Suggestions for dark matter
Dark matter is ponderous material of an unknown kind that is manifested in the motions of stars in galaxies. Alter newtonian gravity on large scales, or the rotation curve method.
Standard Candle
Pulsating yellow giants that have an average luminosity of about 50x that of the sun. Found in RR Lyraes.
High Velocity cloud
Clouds composed of cooler neutral hydrogen gas. They measure about 1000 light years across and contain large amounts of gas.
Local standard of rest
The suns co moving neighborhood of stars. This is the reference frame centered on the sun that moves in a circular orbit around the galactic center at speeds appropriate to the position of the galaxy.
Peculiar motion
The suns movement in relation to neighboring stars.
Sagittarius A
A pointlike object embedded within a hotbed of stellar and gaseous emission. It is observed in the radio continuum.
Stellar population box
Diagrams that help find the rates of star formation. The diagrams measure the horizontal, vertical, and diagonal axes respectively. They refer to the ages, star-formation rates, and metal abundances in galaxies.
Milky Way (Side and above views)
Side (UFO shaped) Above (Large spiral galaxy)
Describe the local group
The local group is the family of about 40 galaxies to which the milky way belongs. There are about three to four spiral or barred galaxies, 5-10 elliptical galaxies, and the rest are irregular.
No dependence on direction
Density fluctuations
Localized enhancements in the density or either matter alone or matter and radiation in the early universe.
a single massive gas cloud dissipates its kinetic and thermal energy by expanding and cooling, then contracting.
Light emitted with a wavelength longer than 912 angstroms produces a cutoff in galaxy spectra that becomes visible in galaxies either viewed from space with the hubble space telescope or from the ground.
Three collapse scenarios for protogalactic gas cloud
1. Nonrotating galaxy where gas does not condense into stars, but instead collapses into a super massive black hole.
2. Rotating galaxy where collapsing gas collisionally dissipates into a thin rotating disk.
3. Slowly rotating galaxy where gas rapidly condenses into stars with a spheroidal distribution of orbits (elliptical galaxy)

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