final exam Flashcards
(97 cards)
1
Q
telescopes
A
gather light and have resolutions
2
Q
resolution
A
make things appear sharper so you can see more detail
3
Q
light gathering power
A
make things brighter––see fainter things. depends on the light collecting area & aperture speed.
4
Q
larger diameter telescopes
A
improve light gathering power and resolving power
5
Q
refracting telescope
A
lens focuses light onto the focal plane
-has chromatic aberration
-difficult and expensive to produce
6
Q
reflecting telescope
A
concave mirror focuses light onto the focal plane. most modern telescopes.
7
Q
chromatic aberration
A
refracting telescopes. different wavelengths are focused at different focal lengths (prism effect). can be corrected, but not eliminated, by second lens out of different material
8
Q
problem w reflecting telescopes
A
the convex mirror must be ground and polished with a precision of less than a wavelength of light. spheres cannot be focused
9
Q
Mt. Wilson 100-inch (Hooker Telescope)
A
used by Edwin Hubble to discover the expanding universe
10
Q
atmosphere density fluctuates
A
light from stars comes in parallel rays until reaching the atmosphere: varying index of refraction bends the incoming light.
11
Q
twinkle of stars
A
wind blowing the density variations
12
Q
“seeing”
A
amount of atmospheric turbulence. good “seeing” is about 1 arcsec, excellent is 90.5 arcsec.
-modern electronics can reduce seeing
13
Q
luminosity
A
total light energy output of the sun. the energy consumption rate.
14
Q
gravitational contraction
A
energy from gravity force. the shrinking of the radius of a star converts potential energy into heat.
15
Q
energy source for the sun
A
1905 theory of special relativity (e=mc2) showed mass and energy are equivalent
the mass of 4 hydrogen atoms is slightly more than 1 helium atom. mass difference is energy.
16
Q
isotopes
A
element’s properties depend on the number of protons, but the number of neutrons can vary without changing chemical properties.
17
Q
fusion energy in the sun
A
mass difference between four hydrogen atoms and one helium atom is converted to energy and released in fusion.
18
Q
Proton-Proton Chain
A
4 H => He :
Act 1: 2H=>D
Act 2: D+H=> 3He
Act 3: 3He+ 3He=> 4He+2H
19
Q
solar neutrino problem
A
only 1/3 the number of neutrinos expected were detected
20
Q
solving the solar neutrino problem
A
neutrinos come in 3 flavors (electron, muon, tau) and only electron neutrinos were detected but when the electron neutrinos from the sun get to earth they mix and the flavors develop
21
Q
flavors of neutrino
A
electron, muon, tau
22
Q
DUNE (Deep Underground Neutrino Experiment)
A
testing the mixing of neutrino flavors over a distance of 800 miles. Uses a huge tank of liquid argon in South Dakota to detect a small fraction of neutrinos from Chicago
23
Q
the apparent magnitude scale
A
brightest stars are 1st magnitude, faintest stars visible to the unaided eye are 6th magnitude.
1st mag appear 100x brighter than 6th.
extends towards negative numbers.
sun = -26.5
full moon = -12.5
sirius = -1.4
24
Q
brightness or flux
A
amount of energy/sec/square meter
25
inverse square law
the flux is the energy received at the Earth per second per square area, the intrinsic luminosity is the true energy per second emitted by the star
26
absolute magnitude
magnitude that a star would have if it were at a distance of 10 parsecs
27
"red clump" standard candle
parallax to stars local to the sun shows a group of stars with an absolute magnitude of -0.2. can be used to estimate distances.
28
spectra of stars
spectra of normal stars show absorption lines, and the lines vary widely.
-OBAFGKM (oh boy an f grade kills me)
-strongest Balmer are stars in the middle
29
harvard computers
1890s harvard hired women to classify stellar spectra : henritta leavitt, annie cannon, celia payne
30
the balmer thermometer
balmer line strength is sensitive to temperature. strongest for medium temperature stars
31
the HR (hertzsprung-russell) diagram
plots the luminosity of stars on the y-axis and the temperature of stars on the x-axis.
luminosity changes are driven by temperature
tells us about the physics of stars and how stars evolve
-main sequence, dwarfs, giants
32
main sequence
radii of stars do not vary by a large amount
33
gaia satellite
measuring parallax to millions of stars in the milky way.
34
color index
B-V measurement
B is star magnitude in blue filter, V is mag in visual filter
Hot stars have small B-V
Cool stars have large B-V
Sun=0.6, Vega=0.0, Betelgeuse=1.9
35
masses of stars in H-R diagram
cool, low luminosity stars have small masses
hot, bright stars have high masses
sun is in the middle
(only true for main sequence stars)
36
Mass-Luminosity relation
luminosity is proportional to stellar mass to the 3.5 power
37
main sequence star lifetimes
massive stars run through fuel quickly. so, high mass stars have the shortest lifetimes.
38
expansion onto Giant branch
expansion and surface cooling during the phase on an inactive He core and a H- burning shell.
young clusters will all be on the main sequence, as they get older the most massive will evolve onto the giant branch, and eventually only the lowest mass will remain on the main sequence.
"turn off" point
39
bright/massive stars
do not live long. we see them where they were born and where they run out of fuel. don't move far from their birth.
40
census of the stars
faint, red dwarfs are most common.
bright, hot, blue main-sequence stars are very rare.
giants and supergiants are extremely rare.
41
stellar evolution of sun-like stars
1-hydrogen exhausted in core. star increases in size and surface cools. moves up giant branch.
2-inert helium core with hydrogen fusion in a shell around the core. core shrinks and heats.
3-helium flash. helium begins fusing in core at the tip of the giant branch.
4-star shrinks and surface gets hotter as it evolves to horizontal branch. helium core burning.
5-helium core burning to carbon on horizontal branch
6-helium exhausted in core. moves up asymptotic giant branch
42
helium fusion
pressure and temperature increase in the helium core until helium can fuse. helium fuses to carbon through the triple alpha process and forms some oxygen too.
43
white dwarfs
remnants of sun-like stars with <8 solar masses. very high luminosity drives away the outer atmosphere of the giant star, leaving the bare core and a nebula of hot gac.
44
planetary nebula
formation of a white dwarf. very hot core of the remaining star after the atmosphere has drifted off.
only result from low-mass stars. expands slowly.
gas is ionized by the stellar core so it glows as electrons recombine. gentle release of outer layers leaves a white dwarf.
45
electron degeneracy
pauli exclusion principle. electrons cannot be squeezed into a small space, this produces a pressure that can balance gravity.
46
pauli exclusion principle
no more than one electron can occupy a quantum state.
47
cataclysmic variable stars
close binary stars––normal star + white dwarf
orbital periods of a few hours
gas often forms an accretion disk around the white dwarf
have optical variabilities
48
optical variability
eclipses
hotspot
disk instabilities
thermonuclear runway
49
eclipses (OV)
orbital periods 1 to 8 hours. orbital modulations. common because stars in CVs are close together. can be used to map the accretion disk light and to time the evolution in orbital period.
50
hotspot (OV)
flickering from stream hitting disk
51
disk instabilities (OV)
"dwarf nova" outbursts including thermal and dynamical instabilities
52
thermonuclear runway (OV)
nova and some supernova explosions
53
novae
hydrogen builds up on white dwarf surface. runway fusion on the outside of the white dwarf. white dwarf and companion survive and will repeat in 20 to 20000 years.
54
supernovae
peak luminosity can be brighter than all the other stars in a galaxy. a bigger novae.
55
thermonuclear supernova TYPE 1A
companion donates mass to white dwarf
fusion starts in the core
radioactive decay energy keeps the supernova bright for months
56
detonation
burning can travel faster than sound speed
57
deflagration
burning can travel slower than the sound speed
58
shock wave
explosions can push the ambient medium faster than the local sound speed.
59
core collapse + bounce
if iron core > 1.4 Msun electron degeneracy can't support it. it shrinks and other layers fall then hit the core and there's a bounce that produces a shock wave that tries to drive the outer layers off
60
supernova classifications
type I, type II
61
type I supernova
type 1a : thermonuclear explosion of white dwarfs
62
type II supernova
core collapse of massive stars. includes types II, Ib, and Ic (don't need to know what those are though)
63
formation of neutron stars
iron core collapse from size of earth to 10km radius.
pressure becomes so high that electrons and protons combine to form stable neutrons
stopped from collapse by neutron degeneracy
64
Pulsars
rapidly spinning magnetic neutron star that produces a regular, fast signal.
magnetic field has a dipole structure, like earth.
they spin kinetic energy into electrical current that causes a radio signal.
65
Milkyway Galaxy
Our galaxy. Disk shaped (galactic disk around it). Galactic bulge in the middle. Galactic halo around. Spiral arms made of young stars. Bulge made of older stars. Mostly made of dark matter.
66
Galaxy
a collection of stars, gas, dust, dark matter, and other material that is gravitationally bound.
67
Spiral arms
caused by spiral density waves, which are compression wages not rigidly rotating and stars move through the spiral arms.
68
Galaxy centers
many galaxies have supermassive black holes in the center.
69
tidal stream
an arc of stars and hydrogen gas formed when a satellite galaxy is pulled apart by the central galaxy's gravity
70
dwarf galaxies
very low-mass galaxies that are almost always found as companions to more massive galaxies
71
spiral galaxy
a galaxy in which the gas, dust, and stars form a spiral pattern. Including the milky way and andromeda. typically newer + bluer.
72
Barred Spiral galaxy
a spiral galaxy that has a shape like a bar in the middle
73
elliptical galaxy
a galaxy that has an ellipsoid shape (like a football)
74
irregular galaxies
asymmetric galaxies that are neither spiral nor elliptical. they tend to be small satellites of larger galaxies.
75
the schwarzchild radius
there is a limiting radius where the escape velocity reaches the speed of light
76
space-time
acceleration is a curving line in the space-time diagram. space and time can't be separated, time must be treated as a 4th dimension. gravity is a warp of space-time. space gets stretched and time slows near masses.
77
View near the event horizon
light will be bent around the black hole: an observer will see the entire sky, even stuff behind the black hole, but the view is compressed into a narrow angle.
78
view near a black hole
at the event horizon the escape velocity is the speed of light so light can't leave. but even before it, the view back gets narrower and narrower.
79
falling into a black hole
crossing the event horizon will be smooth, although the tidal forces may rip you apart. the gravity pull tears apart anything that gets too close.
80
tidal disruption
something getting too close to a lack hole and being shredded. but this is true for other objects as well, like the moon would be torn apart if it got too close to earth.
81
heisenberg uncertainty principle
we cannot know the energy and lifetime of a particle with perfect accuracy: particle pairs can appear out of the vacuum and annihilate a short time later without violating any laws of physics.
82
hawking's discovery
the vacuum near the event horizon will be skewed. sometimes a virtual particle will cross the event horizon while its anti-particle will and won't escape.
proposed that energy will be emitted from black holes due to quantum mechanics.
83
evaporating black holes
a supermassive black hole in the center of a galaxy. a non-accreting black hole can evaporate if they start small.
84
standard candles
sources that have a predictable luminosity
85
Cepheid variable stars
pulsating giant stars. not standard candles, but their luminosity is related to their pulsation period. have periods of days to weeks.
86
instability strip
where pulsating stars are found on the H-R diagram. cepheid variables are evolving through the instability strip.
87
shapely and the milky way center
pulsating stars proved to him that the sun is far from the center of our galaxy.
88
curtis/shapely debate
discussion of the scale of the universe. shapely showed him data that said the MW was very large while Curtis used star counts to argue that it is small, and clusters shapely found were other universes
89
Edwin Hubble
identified cepheid variable stars in the andromeda nebula. couldn't see them in others because they were too faint. published a correlation between estimated distance and velocity of the galaxy.
90
hubble relation
the universe is expanding. galaxies are moving away from each other. H0 is the hubble constant.
91
cepheid distance measurement
repeated brightness measurements allow the determination and the absolute magnitude, therefore distance. they're faint in other galaxies because of dust and crowding.
92
Lemaitre
a theorist that solved equations of general relativity that predicted that the universe was either expanding or contracting, not static.
93
hubble expansion
space itself is expanding. every point in space is getting further from every other point. no center to the expansion.
94
precise hubble constant
early measurements were inaccurate because: most galaxies were too far to use cepheid variables, galaxies are in clusters that create peculiar velocities. need to measure distances greater than 40mpc so that galaxy clustering is not a big error.
95
the cosmic microwave background
the CMB has a black body spectrum. it's uniform in all directions. but temp fluctuations are detected due to small matter density differences.
geometry of the universe is nearly flat–kinetic energy and gravitational energy are equal. atoms make up 5% of the universe, dark matter makes up 27%.
Hubble constant 67.7+/-0.5 km/s/Mpc
96
extending the hubble diagram
instead of expansion slowing down it's accelerating. acceleration requires energy––dark energy.
97
acceleration
universe expansion is accelerating. space will stretch out very quickly. galaxies will red shift away from each other and eventually be undetectable. milky way and adromeda will be the only galaxies surrounded by emptiness.
