Astrophysics Flashcards
1
Q
Units and symbol for mass
A
- mass = m
- units = grams
- grams = g
2
Q
Units and symbol for distance/separation
A
- distance/separation = d or s
- units = meters
- meters = m
3
Q
Units and symbol for speed/velocity
A
- speed/velocity = s or v
- units = meters/second
- meters/second = m/s
4
Q
Units and symbol for acceleration
A
- acceleration = a
- units = meters/second
- meters/second = m/s2
5
Q
Units and symbol for force/weight
A
- force/weight = f or w
- units = newtons
- newtons = N
6
Q
Units and symbol for gravitational field strength
A
- gravitational field strength = g
- units = newtons/kilogram
- newtons/kilogram = N/Kg
7
Q
Define universe
A
The universe is a large collection of billions of galaxies
8
Q
Define galaxy
A
A galaxy is a collection of billions of stars
9
Q
Define solar system
A
A star and many planets orbiting around it
10
Q
Which galaxy is our solar system in?
A
The Milky Way
11
Q
Order the objects found in the known universe smallest to largest
A
Comet, dwarf planet, planet, star, galaxy, universe
12
Q
What is the unit of gravitational field strength?
A
Newtons/kilogram = N/kg
13
Q
Define what gravitational field strength is
A
It is the force in newtons that each kilogram of mass feels, due to the mass of the planet pulling it downwards
14
Q
What is gravitational field strength on earth?
A
g = 9.8 N/kg on earth
15
Q
Are gravitational forces always repulsive or attractive?
A
Always attractive forces
16
Q
What is one thing that gravitational forces do?
A
Keep planets in orbit of each other
17
Q
What is the formula for weight?
A
weight (w) = mass (m) X grav. field strength (g)
18
Q
Give one example of a natural satellite
A
The moon
19
Q
What do satellites orbit?
A
Planets
20
Q
What do planets orbit?
A
Suns
21
Q
What do comets orbit?
A
Suns
22
Q
Two factors affecting the shape of orbits of celestial bodies
A
- mass of both objects
- separation of both objects (how far away they are from each other)
23
Q
What happens to gravitational forces as mass of planet increases?
A
As mass of planets increases, gravitational forces also increase
24
Q
What happens to gravitational forces as separation decreases?
A
The closer the planets are to each other, the greater the gravitational force
25
What is the shape of a comet’s orbit around the sun?
elliptical, and the sun isn’t in the centre
26
Why is a comet’s orbit around the sun elliptical in shape?
- as comet gets closer to the sun, gravitational force increases, so comet gets quickly pulled around the sun
- as it moves away from the sun, gravitational force decreases , so less attraction, so the comet moves slower
27
Define orbital period
time taken for a planet to orbit its star
28
Define orbital radius
Average distance between a planet and its sun
29
What is earth’s orbital period?
1 year = 365.25 days
30
What is earth’s orbital radius?
1AU (astronomical unit) = 15 x 10^6 km
31
Formula for orbital speed
Orbital speed = orbital circumference/orbital period
OR
V = 2 x pi x r / T
32
What is the relationship between orbital radius, orbital sped and orbital period?
The larger the orbital radius, the slower the orbital speed, so the orbital period increases
33
What is the name of the class that stars are classified by?
Spectral class
34
What is spectral class dependent on, and what does this show?
- spectral class is dependent on a star’s colour
- the colour of a star shows its surface temperature
- the bluer a star is, the hotter it is
35
Name the 3 stages that a star goes through during a birth of a star
Gas nebula, protostar, main sequence star
36
Describe and explain a star’s birth
- gravity collapses a cloud of dust and hydrogen gas (gas nebula)
- when the heat and pressure from the collapse is sufficient enough to overcome nuclei repulsion, fusion begins in the protostar
- heat + pressure sustained by fusion in the core balances the gravitational forces that collapse the star
- the star is now stable and a main sequence star
37
Why is a main sequence star hotter than a protostar?
- fusion is constant in a main sequence star
- this means that high levels of heat and pressure are maintained
- whereas in a protostar fusion isn’t constant, so high heat + pressure isn’t maintained
- therefore main sequence stars are hotter
38
Name the 5 stages involved in the death of a low mass star
Main sequence star, red giant, planetary nebula, white dwarf, black dwarf
39
Explain why a main sequence star swells into a red giant at the end of the stable period
- towards the end of the stable period, H2 runs out so fusion of He begins, meaning the surface of the star cools (so reddens) and swells + brightens
- as H2 fusion stops, heat + pressure decreases
- gravitational forces becomes greater than the heat and pressure pushing the star out
- this shrinks the star = becomes denser
- increase in density = HUGE inc. temperature = fusion of helium can start
- release in energy from fusion means that the star can swell many times its original size
- as it expands, it cools and becomes redder = red giant
40
Describe and explain the death of a low mass star
- hydrogen begins to run out so fusion stops and then fusion of He begins = surface cools and become redder + star swells + brightens, becoming a red giant
- as the red giant expands further, gravity loses control of the edges, becoming a planetary nebula as it leaves behind a hot dense core
- the hot dense core is a white dwarf in which fusion no longer occurs in
- the white dwarf cools over time and becomes a black dwarf
41
Name the 5 stages involved in the death of a high/very high mass star
Main sequence star, red supergiant, supernova, neutron star (if high mass) or black hole (if very high mass)
42
Describe the death of a high/very high mass star
- as H2 runs out, the star swells and fusion of heavier elements up to iron begins and continues until there is a large iron core + then fusion stops
- as the star is so large, the stopping of fusion means that the forces sustaining the star are no longer balanced, and the star contracts
- during the star’s collapse, there is such a huge transfer of energy that a massive shockwave is released
- this becomes the only place where elements heavier than iron can be fused + shockwave distributes these in galaxy due to its VERY high pressure + heat
- the core that is left is extremely hot and dense, so dense that there’s no empty space between nuclei = electrons combine w protons, making neutrons, so the star becomes a neutron star
- if the star was very high mass, then the remaining core would be denser bc of the higher gravitational forces acting on them so then it’s gravitational field strength would be so strong that light can’t escape = black hole formed
43
Where were all the elements created?
- light elements up to iron were created in the core of stars by fusion
- elements heavier then iron cannot be fused in the core of stars as there isn’t enough heat + pressure in the core to do this
- the only place where elements heavier than iron can be made are in supernovas, as this is the only place where there’s enough heat and pressure to fuse the heaviest elements
44
What is a star’s life cycle determined by?
The larger its mass, the shorter its life cycle. A star's mass is determined by the amount of matter that is available in its nebula, the giant cloud of gas and dust from which it was born.
45
Compare the rate of fusion in a low mass versus a high mass main sequence star
- larger mass = faster rate of fusion than low mass
- larger mass stars run out of hydrogen faster, as they had more gravitational forces acting on them due to their larger mass, so the higher heat and pressure means more fusion so more heat is released, leading to more fusion of H so that helium is fused into the core earlier
- this process would be much slower in lower mass stars, so lower mass stars have a longer main sequence
46
Compare the temperature in a low mass versus a high mass main sequence star
- high mass stars have a higher rate of fusion = more heat so they are hotter than low mass stars as these have lower rates of fusion so less heat is released
47
Compare the colour of a low mass versus a high mass main sequence star
- high mass stars are bluer
- low mass stars are redder
- this is because higher rates of fusion in high mass stars leads to higher temperatures, therefore the star is bluer in colour as compared to low mass stars, which have a slower version of this
48
Compare the lifespan in a low mass versus a high mass main sequence star
- high mass stars have a higher rate of fusion, so then they exhaust their supply of hydrogen faster than low mass stars
- helium is fused into the core quicker than low mass stars, so they proceed to red supergiant stage faster than a low mass main sequence star would move to a red giant stage
- this means high mass stars proceed through all the stages of their life cycle faster than low mass stars
- therefore they ‘die’ earlier = shorter lifespan
49
What are the three measures in which the brightness of a star can be classified?
- apparent magnitude
- absolute magnitude
- luminosity
50
Define apparent magnitude
How bright a star appears in the night sky
51
What is apparent magnitude dependent on?
- the actual brightness of the star
- how far away the star is from us
52
What is the scale of brightness in apparent + absolute magnitude?
- The brighter the star, the smaller or even more negative it’s magnitude
- so the brightest stars would have a magnitude smaller than 1
- the dimmest stars would have a magnitude greater than 6
53
Define absolute magnitude
How bright a star would be if it was a standard distance (10 parsecs) away
54
Why is absolute magnitude useful?
Allows use to compare the true luminosities of celestial bodies
55
Define luminosity
The total amount of energy radiated by the surface of a star per second in watts
56
What does H-R stand for?
Hertzsprung-Russel
57
Describe the components on a H-R diagram
- y axis = luminosity/absolute magnitude with highest at top + lowest at bottom
- x axis = surface temperature in kelvin running blue on left to red on right (hot to cold)
- bottom left corner = white dwarves
- top right corner = red giants
- top middle = red supergiants
- down the middle in a worm shape = main sequence stars with youngest at top and oldest at bottom + middle of it is the stars going into red giant stage
58
Describe the components on a H-R diagram
- y axis = luminosity/absolute magnitude with highest at top + lowest at bottom
- x axis = surface temperature in kelvin running blue on left to red on right (hot to cold)
- bottom left corner = white dwarves
- top right corner = red giants
- top middle = red supergiants
- down the middle in a worm shape = main sequence stars with youngest at top and oldest at bottom + middle of it is the stars going into red giant stage
59
How old is the universe according to TBBT?
13.75 Billion years old
60
Explain the ideas of TBBT
In this model it is said that the universe expanded from a single point of extremely high temperature + density that radiated gamma, and as it expanded, it cooled and decreased in density, therefore allowing the formation of atoms, molecules, stars and galaxies
61
What are the 2 main pieces of evidence that support TBBT?
- red shift
- CMBR = cosmic microwave background radiation
62
What phenomenon does red shift occur due to?
The Doppler effect
63
What is the Doppler effect?
The apparent shift in wavelength when a source moves relative to an observer. The faster the source moves relative to the observer, the more pronounced the effect
64
Explain red shift and how it supports TBBT
- the more red shifted the light from galaxies appears to be, the faster they are moving away from us
- this is because we know that the speed that galaxies are receding at are directly proportional to their distances away from us
- so the galaxies furthest away from us are moving the fastest away from us
- this provides evidence for an expanding universe (as TBBT suggests) as it suggests that it could’ve expanded from a single point
65
Describe red shift in terms of the Doppler effect
- as the galaxy moves away from earth, the wavelength of light would appear to increase + frequency of light would appear to decrease
- we would observe that the light has moved towards the red end of the spectrum
66
What is CMBR?
Cosmic Microwave Background Radiation
67
Explain CMBR and how it supports TBBT
- TBBT is the only theory that can successfully explain CMBR
- it states that the early universe was very hot and radiated a lot of gamma
- as the universe expanded, the gamma waves stretched
- today they have become microwaves
- as CMBR can be found everywhere, and the universe has expanded for a long period of time, CMBR supports TBBT as it suggests that the universe has expanded from a single point evenly in all directions
68
Recessional speed of galaxy equation
Recessional speed = speed of light X change in wavelength/ original wavelength
