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ASTR 101: FINAL EXAM
terrestrial planet |
small, high-density planet with solid, rocky surface (silicate mantle surrounding Fe-Ni core): Mercury, Venus, Earth, Mars |
jovian planet |
gas giant (thick atmospheres primarily composed of H and He, low densities, large diameters): Jupiter, Saturn, Uranus, Neptune |
differentiation |
geological process by which magma separates into layers of igneous rock of differing density and composition within body; on planetary scale, produces core, mantle, and crust |
Widmanstätten pattern |
cross-hatched pattern on Fe/Ni meteorites, resulting from intergrowth of minerals kamacite and taenite as meteorite parent body slowly cooled in space |
carbonaceous chondrite |
most primitive chondrite meteorite with compositions that most nearly resemble Sun (high [carbon] and [organics]), originating from parent bodies' collision
|
trans-Neptunion object |
small, icy body orbiting Sun beyond Neptune (includes Pluto in Kuiper Belt); scattered-disk objects are in 3:2 orbital resonance and are known as Plutinos
|
Oort cloud |
since new comets approach Sun on highly elliptical orbits at all inclinations, proposal of roughly spherical halo of comet nuclei from formation of solar system out to ~ 100 000 AU
|
comet |
small body, composed of ice and dust, in highly eccentric orbit around Sun (not confined to ecliptic) |
refractory |
element or compound that melts/vaporizes or condenses from gas at high temperature: Al, Ca, U; volatile antonym |
planetesimal |
body of rock and/or ice presumed to have formed in early history of solar system (accumulation = planet formation); most left over from planetary accretion ejected by perturbations of planets into Kuiper Belt and Oort Cloud
|
accretion |
mass of body increases by accumulation of matter (gas or small solid bodies which collide with and adhere), by which bodies in solar system thought to have grown
"core" = planet of 10 solar masses (jovian) can accrete gas directly from nebula |
obliquity (of ecliptic) |
"Earth's axial tilt" = angle between Earth's equator and ecliptic |
photodissociation |
if cool molecular gas cloud is diffuse, all molecules may be dissociated by starlight; photodissociation regions are thereby formed at edges and boundaries
|
gravitational lens |
light rays bent by gravitational field of massive object (galaxy or black hole), seen as formation of double or multiple images of distant galaxy or quasar by a foreground object, or Einstein rings
|
albedo |
reflective property of non-luminous body: 0.0 (blackhole, absorbs all incident light) to 1.0 (mirror); planets or planetary satellites with dense atmospheres > those with transparent or no atmospheres |
reflection spectroscopy |
measures starlight reflected by planet (molecules in atmosphere produce absorption bands due to transitions between different vibrational energy levels) |
Transmission spectroscopy
|
measures star during planetary transit (if planet has atmosphere, some light passes through it and will be absorbed at specific wavelengths) |
hot Jupiter |
planet with mass similar to Jupiter but lying close to its parent star (tidally locked), with nearly-circular orbital period from few days to weeks (believed to have formed farther from parent stars and subsequently moved inwards); first extrasolar planets discovered |
habitable zonE |
orbital region around star where planet might be able to retain liquid water on its surface and possibly support life |
Gravitational scattering |
deflection of object path passing near massive body = large, sudden change in orbital parameters (Jupiter can capture comets in an elliptical orbit or throw them out of solar system)
|
resonance |
period gravitational effect of one object on another = bodies' mutual perturbations repeat at nearly same points in their orbits (building up to produce large oscillations/driving one of bodies into another orbit)
|
planetary migration |
planet towards or away from its parent star as a result of aerodynamic drag from gas, random gravitational interactions with planetesimals, or resonant interactions with other coorbiting bodies (hot Jupiters)
Type I = planet orbits within debris disk, creating density waves (gravitational torque → decreases energy and angular momentum)
Type II = particles in outer debris disk diffuse into gap (due to 10 Solar masses planet formation), causing gap and planet inward
|
interstellar absorption |
absorption of starlight by dust and gas in space between stars; increases towards shorter-wavelength (blue) end of spectrum, hence makes stars appear redder = "interstellar reddening" |
halo |
material in roughly spherical distribution around galaxy: population of old stars (Pop II), including globular clusters, with little to no rotation about galactic centre; highly ionized high-temperature gas; extended distribution of invisible dark matter
|
bulge
|
roughly spherical distribution of stars that forms the central hub of spiral galaxies (older and lower metallicity) |
elliptical galaxy |
Pop II stars, lacking blue stars (no formation for ~ 2 by), and little or no interstellar gas or dust (jets)
dE, D, cD = dwarf, giant, supergiant ellipticals (massive examples found at cluster centres)
|
effective radius |
"half-light radius" = half of galaxy's luminosity is contained |
starburst galaxy |
energy output dominated by radiation from recently formed stars; radiation is emitted mainly in UV region from hot, young massive stars, but is absorbed and re-emitted by dust in interstellar space to give very high luminosities at far infrared wavelengths |
dwarf spheroidal galaxy |
most common type of galaxy in Universe: blue stars ✓, contain little or no interstellar material, not so centrally concentrated (as E. galaxy), have low density, low surface brightness, and a decrease of light output with radius, implying that they are more closely related to small disk galaxies |
spiral galaxy |
bright arms of stars, gas, and dust that extend in a spiral pattern from central hub (spheroidal bulge of Pop II stars) in disk galaxies; spiral arms sites of active star formation, appearance dominated by bright, blue, massive young stars of Pop I and gaseous H II regions |
Population I |
stars (Sun) that lie in disk of galaxy and have high [heavy elements]; probably formed continuously during lifetime of disk from gas enriched by debris from supernovae in Pop II stars |
Population II |
stars found in halo and central bulge of galaxy, with low [heavy elements]; formed in first billion years or so of galaxy's life, before formation of galactic disk |
tidal tail |
consisting of stars pulled away from parent galaxy by gravitational tidal force of another galaxy during close encounter
|
irregular cluster |
loose, clumpy distribution of galaxies with high gas content (undergoing star formation); high fraction of spiral galaxies
|
morphology-density relation
|
clusters having high density have a larger fraction of elliptical and S0 galaxies; within given cluster, early-type galaxies are found primarily in denser regions of cluster
|
mass-to-light ratio |
ratio of total mass to total luminosity expressed in solar units (Sun = 1); (L ~ M^3.5) |
dynamical friction |
Force experienced by mass (star cluster/dwarf galaxy) travelling through extended distribution of stars; gravitational effect of mass as it moves causes slight enhancement of density of stars behind it, and consequent increased gravitational influence acts as drag on mass (merging of galaxies, decay of orbits of globular clusters around galaxies)
|
Seyfert galaxy |
galaxy much like spiral with small, bright nucleus which shows broad, strong emission lines in its spectrum; lower-luminosity examples of quasar activity
Type 1 have broad emission lines of hydrogen but narrow forbidden lines of heavier elements; Type 2 have both broad lines |
quasar
|
object with high redshift which looks like a star, but is actually very luminous active nucleus of distant galaxy; redshifted spectra show strong, often very broad, emission lines as well as continuum radiation |
blazar |
high-speed jet of plasma and radiation (X/gamma) from an active galactic nucleus viewed nearly end-on; broad emission lines in their spectra: low-frequency peak corresponds to synchrotron emission; high-frequency peak results when high-energy electrons collide with photons of cosmic microwave background, boosting them to gamma-ray frequencies (inverse-Compton scattering)
|
M-sigma relation |
mass of central black hole correlates with mass of galactic bulge, as measured by velocity dispersion of stars in bulge: M.BH ∝ σ^5 |
Faber-Jackson relation |
M.BULGE ∝ σ^4; M.BH ∝ M.BULGE^(5/4)
|
aberration |
small apparent difference between observed direction of star and its true direction, due to combined effect of observer's motion across path of incoming starlight and finite velocity of light. |