SVSU PHYS106C Keen Chp 15

Milky way

the spiral galaxy in which our Sun is located

galactic disk

a flattened distribution of stars and interstellar material within a galaxy

spiral galaxy

a pinwheel shaped galaxy that may have spiral arms

spiral arm

a pinwheel-shaped distribution of stars and interstellar material, typically extending from the bulge outward

peculiar motion

the motion of stars in the Milky Way disk that is a departure from pure revolution around the galactic center

metallicity

the abundance of elements heavier than helium in an object

Population 1

a category of stars, found primarily in the disk or bulge, that have a high metallicity and therefore must have been born relatively recently in cosmic history

stellar halo

the spherical distribution of Pop 2 stars that are found mainly in globular clusters

Population II

stars found primarily in the stellar halo, which have lower metallicity and therefore must have been born relatively early in cosmic history

bulge

the roughly spherical distribution of stars and interstellar material in the central region of a galaxy

Local group

a gravitationally bound collection of galaxies within which the Milky Way resides

spiral density wave

a wavelike pattern of compression that moves through the physical material of a galaxy's disk. Spiral density waves are seen in spiral arms

compression wave

a wave of increased density that passes through background material; the density returns to normal after the wave passes

instability

a complex pattern of gas flow resulting from a disruption in an originally smooth flow

molecular ring/disk

a dense ring of molecular material orbiting the galactic center

starburst

a rapid conversion of an appreciable fraction of molecular gas into stars

rotation curve

the graph of rotation speed as a function of orbital radius for objects orbiting a common center, such as stars orbiting a galaxy

dark matter

nonluminous mass that is evident only by its gravitational influence

massive compact halo object (MACHO)

A proposed form of dark matter that includes objects such as black holes and extremely faint neutron stars

fundamental forces

the four basic ways matter can interact: gravity, electromagnetic force, the strong nuclear force, and the weak nuclear force

weakly interacting massive particle (WIMP)

a proposed form for dark matter consisting of particles that interact only via gravity and the weak nuclear force