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Physics YEAR 1 and 2 > ASTROPHYSICS > Flashcards

ASTROPHYSICS Flashcards

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1
Q

what is a planet

A

an object around a star with a mass large enough for its own gravity to give it a round shape, that does not undergo nuclear fusion and that has cleared its orbit of most other objects.

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2
Q

what is a satellite

A

a body in orbit around a plant

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3
Q

what is a comet

A

a small irregular body made of dust, ice and rock that orbits a star, with highly elliptical orbit

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4
Q

what is a solar system

A

a planetary system consisting of a star and at least one planet in orbit around it

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5
Q

what is a nebula

A

a star forming region

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6
Q

what happens to the helium/hydrogen energies when the gravity pulls the molecules close together

A

the potential energies decrease and the kinetic increases.

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7
Q

what is the second stage of star formation called

A

protostar

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8
Q

what happens to the density, pressure and temp in a proto star

A

the centre becomes more dense meaning temp and pressure increase

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9
Q

why does fusion happen in stars

A

the kinetic energy increases as density increases, so this force overcomes the electrostatic repulsion.

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10
Q

what acts against the gravitational force in a star

A

the radiation/gas pressure

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11
Q

what is the first energy level called?

A

ground level

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12
Q

what happens when an electron moves down a shell

A

a small quanta of energy is released, as a coloured photon

E=hf

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13
Q

what colour will the photon be if it moves from n1 shell to ground shell? red or blue?

A

blue, larger frequency and energy

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14
Q

what happens if you excite a gas

A

the electrons on the energy levels will drop down and emit certain frequencies of light

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15
Q

what is wiens displacement law

A

max intensity is inversely proportional to T

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16
Q

what is wiens constant

A

2.9x10^-3

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17
Q

define luminosity and what its proportional to

A

total amount of energy emitted per second

4πr^2ΣT^4

Σ is 5.67x10^-8

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18
Q

what is a galaxy

A

a cluster of billions of starzz. which rotate around a galaxys centre of mass.

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19
Q

define gravitational collapse

A

when a star collapses in on itself due to gravitational force caused by its own mass. when the radiation pressure cannot withstand the gravitational force.

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20
Q

define radiation pressure

A

is due to the momentum of the photons released in fusion reactions, acting outward

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21
Q

define the main sequence

A

a star in its cycle when hydrogen is forming helium in its core,

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22
Q

hat is a white dwarf

A

end product of a low mass star. very dense, outer layers have dispersed into space. high surface temp. low luminosity

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23
Q

electron degeneracy pressure,

A

pressure that stops the collapse of a low. mass star. acts against gravitational force,

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24
Q

chandrasekhar limit

A

the maximum possible mass for a stable white dwarf

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25
Q

what is a red super giant

A

exhausted all the hydrogen in its core and has a mass much higher than the sun

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26
Q

what is a neutron

A

W1

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27
Q

what are the symbol for light years

A

Ly

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28
Q

what is a parsec

A

when the angle theta is equal to one second of arc, then the distance ( adjacent ) is 1 parsec.

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29
Q

what is 1 second of arc

A

circle - 360º
1º=60 mins
1 min= 60 seconds
so 60th of a 60th of 360

its a very small angle, 1/3600

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30
Q

what is electron degeneracy pressure

A

when matter is compressed, there is not enough space for electrons to move around. the forces force the electrons into the lowest energy levels. electrons exert a repulsive force. This is known as electron degeneracy pressure. only sufficient to prevent collapse.

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31
Q

stellar remnants

A

the collective term for white dwarfs, neutron stars, and stellar-mass black holes

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32
Q

what happens when the mass of an iron core goes over 1.4 solar masses (chandrasekhar limit)

A

the electron degeneracy pressure cannot keep the star stable, so the star collapses.

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33
Q

what is super novae

A

loss of gravitational potential energy would release energy produces intense heating.
protons and electrons form together under immense gravitational pressure to form neutrons. triggers an explosion.

34
Q

what is a neutron star

A

after a supernova, the dense collapsed neutron core may stay intact, this is a neutron star.

35
Q

how is a black hole formed

A

Most black holes form from the remnants of a large star that dies in a supernova explosion. (Smaller stars become dense neutron stars, which are not massive enough to trap light.)

36
Q

what can you say about the gravitational field around a black hole

A

immensely large. will be so strong that not even light can escape.

37
Q

what is a continuous spectrum

A

a spectrum which contains all the wavelengths over a comparatively wide range

38
Q

what are energy levels

A

inside an atom are the specific energies that electrons can have when occupying specific orbits. electrons can only stay in these specific orbits, none in between.

39
Q

what is the emission line spectrum

A

a spectrum of the frequencies of electromagnetic radiation emitted due to electron transmissions from higher to lower energy levels.consists of a series of bright light against a dark bachground.

40
Q

what is an absorption line background

A

is the pattern of dark lines in a continuous spectrum from a light source and is caused by light passing through an absorbing medium such as gas. dark lines represent wavelengths that are absorbed

41
Q

what is a transmission diffraction grating

A

is a glass surface having a large number of very thing parallel grooves, used to produce optical spectra by diffraction of transmitted light.

42
Q

what happens when a frequency of light is absorbed by an electron.

A

the electron moves up and then down an energy level. the E=hf, so the electron changing energy emits a photon with the same frequency of light in 360º of direction.

43
Q

what happens to the mean wavelength of light when the emitter gets hotter

A

it decreases proportionally

wavelength- 1/t

44
Q

what is astronomical unit

A

the mean distance between the earth and the sun, so 1.5x10^11 m

45
Q

how much distance is a light year

A

9.46x10^15

46
Q

parallax = 1/?

A

parallax = 1/d

47
Q

explain carbon dating

A

the big bang produced a lot of heat, there is a lot of heat left over, the universe is about 2.7k. we can still se primordial elements.

48
Q

what is the cosmological principle

A

the universe is isotropic and homogeneous

49
Q

the future of the universe may be open closed or flat, explain what these terms mean

A

flat; the universe expands to a limit but never reaches
open; expands for all time
closed; shrinks back, contracts

50
Q

The Friedmann equation

A

h^2=1/3(densityx8xπxG)

51
Q

What is Gravitational Collapse

A

Thin clouds of interstellar dust, containing hydrogen and helium, form clusters.
When they are large enough, the clusters begin to collapse under their own gravitational force

52
Q

What is atomic fusion

A

As the cluster contracts, the remp increases to 10^6 degrees, when nuclear fusion occurs, with helium being produced from hydrogen. In thus state the star produces a huge amount of heat and light. It is a main sequence star

53
Q

Radiation and Gas Pressure

A

The photons emitted by the very hot, bright star, transfer some momentum to the hydrogen that would otherwise collapse under gravitational pressure.

54
Q

what are characteristics of white dwarfs

A

at the end of stellar evolution for low to medium mass star like the sun. Very dense. Very hot. low luminosity.

55
Q

What is electron degeneracy pressure

A

As the white dawrf compresses material together, high energy electrons produce a pressure outwards which balances the gravitational force inwards.

56
Q

what is the chandrasekhar limit

A

1.4 solar mass. If the mass of a white dwarf is over this then the star would continue to collapse into a neutron star or black hole.

57
Q

what happens when an electron emits a photon

A

drops down a level and vice versa if it absorbs a photon

58
Q

what does a cool gas mean

A

atoms are in their ground states

59
Q

calculate the critical density of the universe

A

3H^2/8πG

60
Q

what is dark matter

A

Matter which cannot be seen and that does not emit or absorb electromagnetic radiation, It is not detected directly but it is detected indirectly based on its gravitational effects.

61
Q

what is dark energy

A

is a type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies via the exertion of negative pressure.

62
Q

What is a WIMP

A

weakly interacting massive particle

63
Q

describe evidence for the hot big bang theory

A

galaxies are moving further apart,
there is excess helium in the universe
2.7 kelvin background radiation present
evidence in red shift

64
Q

describe evidence for the hot big bang theory

A

galaxies are moving further apart,
there is excess helium in the universe
2.7 kelvin background radiation present
evidence in red shift

65
Q

State olbers paradox

A

the night sky should be bright, but its not. Number of stars is proportional to r^2 and intensity is 1/r^2

66
Q

?=(change in λ/ λ) x c

A

V

67
Q

state two types of energy produced in thermo nuclear reactions

A

kinetic and electromagnetic

68
Q

light moving towards vs light moving away equation

A
69
Q

why does the sun lose mass in order to maintain luminosity

A

fusion reactions occur which change H in He, meaning energy is released =c^2m
m per second=luminosity / c^2

70
Q

why does the sun require a high temperature which provides energy for fusion

A

average k.e. of each proton is 3/2kT
high temperatures means protons are travelling at high speed, fast enough to overcome repulsive forces
close enough to fuse together.
p.e. q^2/4πε0r so T must be high enough for 3/2kT> q^2/4πε0r

71
Q

describe the formation of a low sequence star

A

dust and gas slowly come together, through gravitational attraction between atoms. these areas become more dense over time, resulting in a gravitational collapse.
more matter is collected into the clump of matter, kinetic energy increases causing the temperature to rise. this large core is a protostar. the protostars gravitational field will start to collect more mass until the temp and pressure of a star become too much. fusion reactions in the core will start to occur. hydrogen will fuse to create helium nuclei and two gamma rays and two neutrinos and two positrons. this will cause radiation pressure. when the gravitational and radiation forces are stable, the star is main sequence.

72
Q

what is electron degeneracy pressure

A

when matter is very compressed, electrons are no longer free to move about energy levels. As the star contracts, electrons from neighbouring atoms are forced into the lower energy levels and then into higher ones once the lower levels are filled. when all available electron states are full then electrons exert an outer force. this is known as electron degeneracy pressure.

73
Q

what is the fate of high mass stars

A

when they move off the main sequence, they are much brighter than lower mass stars. the core contracts and increases temp while the outer layer of the star increases size to become a red supergiant the core heating up allows more nuclear fusion to occur, continuing until an iron core builds up, this then collapses. if the mass is over the chandrasekhar limit (1.4) solar masses the star will remain a white dwarf. if it is greater than this then the electron degeneracy pressure will. not be able to keep it stable and it will therefore turn into a gravitational collapse.

74
Q

how is a supernovae formed

A

electrons and protons form into neutrons causing an explosive of the outer shell. (huge release of energy)

75
Q

how are neutron stars formed

A

under certain conditions, the extremely dense collapsed neutron core can remain intact after the explosion.

76
Q

how are black holes formed

A

when the star is greater than three to four solar masses.the pressure on the core would be so large that the neutron would collapse to a point that the density would become infinite.the gravitational field is so strong that this region is known as a black hole.

76
Q

how are black holes formed

A

when the star is greater than three to four solar masses.the pressure on the core would be so large that the neutron would collapse to a point that the density would become infinite.the gravitational field is so strong that this region is known as a black hole.

77
Q

what is weins law

A

objects of different temperatures emit spectra that peak at different wavelengths. lamda is inversely proportional to Temp

78
Q

what is stephans law

A

the luminosity of a star is the total energy that the star emits per second .

79
Q

evidence of the big bang

A

background radiation, temperature 2.7 k ,

Physics YEAR 1 and 2 (24 decks)

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