Midterm 2 Flashcards
(50 cards)
1
Q
Types of Binary Star Systems
A
- Visual binary
- Spectroscopic binary
- Eclipsing binary
2
Q
How do we measure stellar luminosities?
A
- Measure apparent brightness and distance
- Luminosity = 4(pi) (distance)^2 x (brightness)
3
Q
How do we measure stellar temperatures?
A
- Color
- Spectral type
4
Q
How do we measure stellar masses?
A
- Only possible for binary star systems
- Find orbital period and average orbital separation
- Use Kepler’s third law (Newton’s version)
p2 = [4(pi)2/g(m+m)]*a3
5
Q
What is a Hertzsprung-Russell diagram?
A
- A plot of stellar luminosity vs surface temperature
6
Q
What is the significance of the main sequence?
A
- Normal stars that fuse H to He are main sequence
- A star’s mass determines its position
- high-mass: luminous, blue, hot
- low-mass: faint, red, cool
7
Q
Giants/supergiants
A
When core hydrogen is exhausted stars rapidly release fusion energy and become redder, cooler, larger
8
Q
Why do the properties of some stars vary?
A
- Failure to keep balance between power generated in the core and power radiated from the surface
9
Q
Where do stars form?
A
- T: 10-30K
- Clouds of molecular hydrogen stay cool because they emit carbon monoxide
10
Q
What is the smallest mass a newborn star can have?
A
- Below 0.08Msun degeneracy pressure stops contraction before fusion starts
11
Q
What is the greatest mass a newborn star can have?
A
- Greater than 300MSun stars would be so luminous that radiation pressure would blow them apart.
12
Q
What are the typical masses of newborn stars?
A
- More low-mass stars than high-mass stars are formed
13
Q
How does a star’s mass affect nuclear fusion?
A
- Mass determines core pressure and temperature determines fusion rate.
- Higher mass stars have higher fusion rates, luminosities, hotter cores, and shorter lifetimes.
14
Q
What are the life stages of a star?
A
- Hydrogen fusion in core (main sequence)
- Hydrogen fusion in shell around contracting core (red giant)
- Helium fusion in core (horizontal branch)
- Double shell burning (red giant)
15
Q
How does a low-mass star die?
A
- Hydrogen and helium are ejected in a planetary nebula leaves behind an inert white dwarf.
16
Q
What is different between high-mass and low-mass stars?
A
High-mass have higher core temperatures that allow fusion of heavier elements necessary for life
17
Q
How does a high-mass star die?
A
The iron core collapses into a supernova
18
Q
How does a star’s mass determine its life story?
A
- Core temperature
- How rapidly fuel is used
- The elements it produces
19
Q
Two types of supernovae
A
- Massive star supernova
- White dwarf supernova
20
Q
Massive star supernova
A
- Iron core reaches white dwarf limit
- Collapses into neutron star
- Leaves behind nebula and neutron star
21
Q
How does a white dwarf supernova happen?
A
- In close binary system an accretion disk forms when matter from its companion falls on it
- The white dwarf limit is reached and carbon fusion ignites and explodes (as a nova or supernova)
- leaves behind nebula
22
Q
How is a white dwarf formed and maintained?
A
- After fusion has ceased most stars leave behind a white, hot, small core
- Electron degeneracy pressure prevents collapse
23
Q
Neutron star
A
- Ball of neutrons supported by neutron degeneracy pressure
- Tiny radii, massive (corpse of high-mass star)
24
Q
How were neutron stars discovered?
A
- Observations of beams of radiation from a rotating neutron star that appear to pulse (like lighthouse beams).
25
Three populations of dead stars:
- White dwarfs (least massive and most abundant)
- Neutron stars (more massive and less abundant than white dwarfs)
- Black holes (most massive and least abundant of the three populations)
26
What does our galaxy look like?
- A disk of stars and gas
| - A bulge at the center surrounded by a large spherical halo
27
How do stars orbit in our galaxy?
- Disk stars: orbit in circles going in the same direction with small up-and-down motion
- Halo and bulge stars: random orientations
28
How is gas recycled in our galaxy?
- Gas from dying stars mixes new elements into the interstellar medium
- It slowly cools, making the molecular clouds
- Stars form in the clouds and return their matter to interstellar space
29
Where do stars tend to form in our galaxy?
- Molecular clouds and ionization nebulae.
| - Most form in the spiral arms in our galaxy
30
What clues to our galaxy's history do halo stars hold?
- Halo stars are all old
- Less heavy elements than disk stars
- The halo in our galaxy must have formed first.
31
How did our galaxy form?
- Halo stars formed first
| - Disk stars later, after the gas settled into a spinning disk.
32
How are the lives of galaxies connected with the history of the universe?
Galaxies generally formed when the universe was young and have aged along with the universe.
33
What are the three major types of galaxies?
- Spiral galaxies
- Elliptical galaxies
- Irregular galaxies.
34
How do we measure the distances to galaxies?
- Use parallax measurements, relationship between luminosity, distance, and brightness
- Calibrate white dwarf supernovae as standard candles.
- (To measure distances greater than 10 billion light-years)
35
How old is the universe?
13.6 Billion years
36
How did Hubble prove that galaxies lie far beyond the Milky Way?
He measured the distance to the Andromeda Galaxy using Cepheid variable stars as standard candles.
37
What is Hubble’s law?
The faster a galaxy is moving away from us, the greater its distance:
Velocity = H0 x Distance
38
How do distance measurements tell us the age of the universe?
- The distance and speed of a galaxy allows us to figure out how long the galaxy took to reach its current distance
39
How does the universe’s expansion affect our distance measurements?
Three distances:
- Distance at photon emission
- Photon travel distance or lookback distance (default distance reported by astronomers)
- Distance today
40
Visual binary star system
Orbital motion is directly observable
41
Spectroscopic binary star system
Orbit is determined by measuring Doppler shifts
42
Eclipsing Binary
Orbit is determined by measuring periodic eclipses
43
Luminosity
Amount of power a star radiates
44
Parallax
Tells us distances to the nearest stars.
45
The colour of a star tells:
Temperature: Hotter objects emit more light per unit area at all temperatures and have higher photon energy
46
The spectral type of a star tells:
Temperature: Absorption lines indicate ionization level
47
7 Spectral types
O B A F G K M
48
What is the difference between spiral and elliptical galaxies?
Spirals have both disk and spheroidal components; ellipticals have no disk.
49
Parallax measurements
Build on radar ranging in our solar system.
50
Expansion rate of the universe
Hubble's constant
