Astrophysics Flashcards
1
Q
solar system
A
eight planets that orbit the sun
2
Q
asteroid
A
small rocky body that drifts around the solar system
3
Q
meteriod
A
asteroid on a collision course with another planet
4
Q
meteorites
A
small meteors can be vaporized due to the friction with the atmosphere - the bits that arrive on earth
5
Q
comets
A
mixture of rock and ice in very elliptical orbits around the Sun - their tails always point away from the sun
6
Q
nebulae
A
interstellar clouds of dust, hydrogen, helium and other ionized gases
7
Q
constellation
A
patterns of stars have been identified and 88 different regions of the sky have been labelled
8
Q
why do the constellations seem to rotate?
A
result of the rotation of earth about its own axis
9
Q
describe the movement of the sun during the day and during the year
A
sun rises in the east and sets in the west winter to summer, arc gets bigger and the sun climbs higher in the sky
10
Q
light year
A
distance travelled by light in one year
11
Q
milky way
A
faint band of light in the night sky
12
Q
why is the milky way seen to be a band?
A
galaxy has a spiral shape
13
Q
describe the movement of the galaxy.
A
- rotating
- all the stars are orbiting the centre of the galaxy as a result of their mutual gravitational attraction
14
Q
stellar clusters
A
stars are grouped
15
Q
what are the two types of stellar clusters?
A
open or globular
16
Q
open stellar cluster
A
containing 10^3 stars
17
Q
globular stellar cluster
A
containing 10^5 stars
18
Q
what is the vast majority of space?
A
vacuum
19
Q
what is the source of energy for stars?
A
fusion of hydrogen into helium nuclear reaction
20
Q
what is the reaction for the energy of stars?
A
411p –> 42He + 201e+ + 2v
21
Q
where does the hydrogen fusion take place?
A
core of the star
22
Q
how is the sun stable?
A
there is hydrostatic equilibrium between the outward pressure and the inward gravitational force
23
Q
binary stars
A
two or more stars orbit around their common centre of mass
24
Q
what are the different categories of binary star?
A
- visual
- spectroscopic
- eclipsing
25
visual binary star
one that can be distinguished as two separate stars using a telescope
26
spectroscopic binary star
* identified from the analysis of the spectrum of light from the 'star'
* over time the wavelengths show a periodic shift or splitting in frequency
* involves the Doppler effect
27
Doppler effect
* as a result of its orbit, the stars are sometimes moving towards the earth and sometimes moving away
* when a star is moving towards the earth, its spectrum is blue shifted
* when a star is moving away from the earth, its spectrum is red shifted
28
eclipsing binary star
* identified from the analysis of the brightness of the light from the 'star'
* over time the brightness shows a periodic variation
29
explain the 'dip' in brightness for an eclipsing binary star.
* as a result of its orbit, one star gets in front of the other
* if the stars are of equal brightness, this causes the brightness to drop by 50%
30
parallax
an object that is near to you will appear to move away when compared with objects that are far away
31
explain why after a period of a year some stars can appear to move between two extremes.
* the earth has moved over this period
* means that a close star will have an apparent movement when compared with a more distant set of stars
* the closer a star is to earth, the greater the parallax shift
32
luminosity
* total power radiated by a star
* watts
33
apparent brightness
power recieved per unit area
34
what would happen if two stars were the same distance away from the earth but one has a greater luminosity?
the one with greater luminosity would be brighter
35
what is the issue with apparent brightness?
two stars can have the same apparent brightness even if they have different luminosities
36
what are the alternative units for luminosity?
* apparent magnitude
* absolute magnitude
37
are stars considered black bodies?
yes
38
how to analyse the absorption spectra of stars?
missing wavelengths correspond to a number of elements
39
spectral class
stars that emit the same type of spectrum are allocated to the same spectral class
40
what are the seven main spectral classes?
1. O
2. B
3. A
4. F
5. G
6. K
7. M
41
red giant stars
* large in size
* red in color
* comparatively cool
* one of the later possible stages for a star
* source of energy is fusion of elements other than hydrogen
42
white dwarf stars
* small in size
* white in color
* comparatively hot
* one of final stages for some smaller mass stars
* fusion not taking placce
* hot remnant that is cooling down
* eventually will cease to give out light when it becomes sufficiently cold (brown dwarf)
43
cepheid variables
* little unstable
* regular variation in brightness and luminosity
* due to an oscillation in the size of the star
44
neutron stars
* post-supernova remnants of some larger mass stars
* gravitational pressure forces total collapse
* mass composed of neutrons
* enormous density
45
pulsar
rotating neutron star
46
black hole
* post-supernova remnant of larger mass stars
* no known mechanism to stop the gravitational collapse
* escape velocity greater than speed of light
47
nucleosynthesis
creation of nuclei of different elements as a result of fission reactions
48
what are the necessary conditions for nucleosynthesis to take place?
* two positively charged particles need to come close enough for interactions to take place
* will repel one another so must be at a high temperature
49
What occurs if a cloud of hydrogen is hot enough?
nuclear reactions take place spontaneously
50
how is the temperature of a star constant?
power radiated by the star is balanced by the power released in these reactions
51
how is the size of a star stable?
outward pressure of the radiation is balanced by the inward gravitational pull
52
how does a cloud of hydrogen get to be a high temperature in the first place?
as the cloud comes together the loss of gravitational potential energy must mean an increase in kinetic energy and hence temperature
53
Hertzsprung-Russell Diagram
* what are its axes?
* what does it show?
* vertical axis is the luminosity of the star compared to that of the sun
* horizontal axis is a scale of decreasing temperature
* each dot represents a different star
54
What is the essential difficulty presented by parallax shifts?
when we observe light from a very distant star we do not know the difference between a bright source that is far away and a dimmer source that is closer
55
standard candle
star of known luminosity
56
cepheid variable star
* standard candle
* outer layers undergo a periodic compression and contraction and this produces a periodic variation in its luminosity
57
can a star continue in its main sequence state forever?
* no
* at some point the hydrogen in the core will become rare
* fusion reaction will happen less often
* star is no longer in equilibrium
* gravitational force will cause the core to collapse
* increases temperature of the core so further hydrogen and helium fusion is possible
* star increases massively in size
* become red giant star
58
what does the process of fusion as a source of energy end with?
* nucleosynthesis of iron
* has one of the greatest binding energies per nucleon of all nuclei
* fusion of iron to form a higher mass nucleus would need to take in energy rather than release energy
59
chandrasekhar limit
equal to approximatelly 1.4 times the mass of our sun
60
what happens below the chandrasekhar limit?
electron degeneracy pressure
61
fate for a star below the chandrasekhar limit
* red giant forms a planetary nebula
* become a white dwarf
* become invisible
62
fate for a star above the chandresekhar limit
* experiences supernova
* becomes a neutron star or collapses to a black hole
63
oppenheimer-volkoff limit
* largest mass a neutron star can have
* remnants above this limit will form black holes
64
H-R diagram
all possible evolutionary paths for stars
65
evolution of a low mass star
66
evolution of a high mass star
67
pulsar
cosmic source of very weak radio wave energy that pulsate at a very rapid and precise frequency
68
what would a rotating neutron star be expected to emit?
* intense beam of radio waves in a specific direction
* as a result of the star's rotation, this beam moves around and causes the pulsation that we recieve on earth
69
quasars
* point-like sources of light and radio waves that are very far away
* red shifts are very large
* at limit of our observations of the universe
70
expansion of the universe
* almost all galaxies show red shifts
* rate of expansion should decrease as result of gravitational attraction between all the masses in the universe
71
is earth at the centre of the universe?
* no
* any galaxy would see all the other galaxies moving away from it
72
big bang
* creation of the universe
* all the matter in the universe was crushed together
* since the big bang universe has been expanding
* creation of space and time
73
cosmic microwave background radiation
* microwave radiation is coming towards us from all directions in space
* not always linked to a sources
74
what are the two ways of understanding CMB radiation?
1. all objects give out electromagnetic radiation
2. some time after the big bang radiation became able to travel through the universe
75
are the galaxies distributed evenly across the universe?
no - clustered together
76
what is the trend regarding the speed of distant galaxies?
moving away at a greater speed as the universe expands
77
Hubble's law
general trend for galaxies is that the recessional velocity is proportional to the distance away from the earth
78
supernova
catastrophic explosions that can occur in the development of some stars
79
type I vs type II supernova
* no hydrogen in type I
* hydrogen in type II
80
how can cepheid variables be used to determine the distance to a galaxy?
1. cepheid variable is standard candle so have different way to find luminosity
2. use luminosity, state brightness equation
3. about same distance to whole galaxy bc variable is in that galaxy
81
how can the parallax angle be used to measure the distance of a star?
tanσ = (distance from Earth to Sun)/(distance from Sun to Star)
82
describe the characteristics of a cepheid variable
* always same intensity
* as size increases, luminosity increases and brightness increases
83
standard candle advantage
have different way to find luminosity tied to period
84
why does cosmic background radiation provide evidence for the big bang?
* CBR is the same in all directions
* consistent with cooling off from big bang
85
is the universe expanding?
no - space itself is expanding
