5.5 Astrophysics and cosmology Flashcards
(175 cards)
1
Q
What is nuclear fusion?
A
Nuclear fusion is the process of two nuclei joining together and releasing energy from a change in binding energy.
2
Q
Describe a galaxy.
A
A galaxy is a cluster of many millions of billions of stars. Starts in a galaxy rotate around the galaxy’s center of mass.
3
Q
How many years does it take for the sun to undo go one complete revolution of the galaxy?
A
230 million years
4
Q
How do stars form?
A
Stars are formed when huge amounts of matter, gas or interstellar dust, are pulled together under the force of gravity. If there is enough matter to create the right conditions of extremely high temperature and density, nuclear fusion begins, releasing enormous amounts of energy as electromagnetic radiation.
5
Q
What gas mostly makes up stars, what does this fuse to?
A
The vast majority of the gas present is hydrogen, which fuses into helium.
6
Q
What is the mass of the sun?
A
2x10^30kg
7
Q
Define a planet.
A
Bodies that move in circular or elliptical orbits around a star to form a solar system.
8
Q
How are planets formed?
A
Planets are formed when interstellar dust is attracted into larger clumps, which accrete to form larger bodies.
9
Q
What planets are being formed, why doesn’t nuclear fusion occur?
A
During the formation of a planet, there is less matter involved compared to when a star is being formed. This means planets don’t give out their own light.
10
Q
What are planetary satellites?
A
Smaller bodies than the planets themselves can orbit the planet. For example, the earth has one planetary orbit called the moon.
11
Q
How long does it take for the moon to complete a full revolution of the earth?
A
Just over 27 days.
12
Q
What are comets?
A
Comets are large, rocky ice balls that travel in highly elliptical orbits around the sun.
13
Q
How long ago was the big bang?
A
13.8 billion years ago.
14
Q
What is the diameter of the observable universe?
A
93 billion light years.
15
Q
What is gravitational collapse?
A
Gravitational collapse is the inward movement of material in a star due to the gravitational force caused by its own mass. Star formation is due to the gradual gravitational collapse of a cloud of gas and dust. Gravitational collapse occurs in a mature star when the internal gas and radiation pressure can no longer support the star’s own mass.
16
Q
What is radiation pressure?
A
Radiation pressure is due to the momentum of photons released in fusion reaction, and acts outwards (in the direction of the energy flow).
17
Q
What is the main sequence in the life cycle of a star?
A
A main sequence star is a star in the main part of its life cycle, where it is fusing hydrogen to form helium in its core.
18
Q
What is a main sequence start shown as?
A
The main sequence stars are shown as a curved band on a plot of a star’s luminosity against temperature.
19
Q
What is a red giant?
A
A red giant is a star in the later stages of its life that has nearly exhausted the hydrogen in its core and is now fusing the helium nuclei. It is bigger than a normal star because the surface layers have cooled and expanded.
20
Q
What is a white dwarf?
A
A white dwarf is the end product of a low-mass star, when the outer layers have dispersed into space. A white dwarf is very dense, with a high surface temperature and low luminosity.
21
Q
What is a planetary nebula?
A
A planetary nebula is an expanding, glowing shell of ionised hydrogen and helium ejected from a red giant start at the end of it’s life.
22
Q
What is electron degeneracy pressure?
A
Electron degeneracy pressure is the pressure that stops the gravitational collapse of a low-mass star. This is the pressure that stops a white dwarf star from collapsing.
23
Q
What is the Chandrasekhar limit?
A
The Chandrasekhar limit is the maximum possible mass for a stable white dwarf star and it equal to 1.4 times the mass of our sun. White dwarfs with masses above this will collapse further to become neutron stars or black holes.
24
Q
What is a red super giant?
A
A red super giant is a star that has exhausted all the hydrogen in its core and have a mass much higher than the sun.
25
What is a supernova?
A supernova is a huge explosion produced when the core of a red giant collapses.
26
What is a neutron star?
A neuron star is the remains of the core of a red super giant after it has undergone a supernova explosion. It is incredibly dense and composed of mainly neutrons.
27
What is a black hole?
A black hole is the core of a massive star that has collapsed almost to a point. Black holes are very dense and very small, with a gravitational field strength so strong the light cannot escape (the escape velocity is greater than the speed of light).
28
What is a Hertzsprung-Russell (HR) diagram?
A Hertzsprung-Russell (HR) diagram is a luminosity-temperature graph.
29
Define luminosity of a star.
The luminosity of a star is the total energy that the star emits per second.
30
What is a protostar?
As the gravitational force pulls more and more matter together, work is done on the particles of gas and dust, leading to an increase in kinetic energy. This results in an increase in temperature until some of the denser areas of gas become hot enough to glow. This large core of material is called a protostar.
31
How can protostars be detected?
Protostars can only be detected through telescopes designed to observe infrared radiation, as the clouds of gas and dust around them (nebulae) absorb and scatter most visible light.
32
What happens once the temperature and pressure of the protostar becomes much greater?
The star will reach millions of degrees kelvin and the increased kinetic energy increases the chance of fusion reactions will begin.
33
What happens during a fusion reaction in a protostar?
Thew overall effect of the fusion of hydrogen nuclei to helium nuclei is that 4 protons are 1 helium-4 nucleus with the production of 2 gamma ray photons, 2 neutrions and 2 prositrons. During this enourmous amount oif energy will be produced.
34
What does the momentum of photons released by fusion lead to?
Leads to an outwards force called radiation pressure.
35
In a star of stable size, what will the radiation pressure be equal to?
The radiation pressure and the gas pressure are in equillibrium.
36
What is the inwards gas pressure in a star caused by?
The kinetic energy of the gas atoms.
37
When a star has a radiatrion pressure and a gas pressure in equilibrium, what stage if it's life is it at?
It is a main sequence star.
38
At what stage will a star remain for the majority of it's life?
When it is a main sequence star.
39
What do main sequence stars fuse in their cores?
They fise hydrogen to make helium in their cores.
40
What is the mass of a main sequence star in regards to the sun?
The mass of a main sequence star can vary about 10% of the mass of the sun up to 200 times the mass of the sun.
41
How does a stars life time change depending on it's mass?
The greater the mass of a star, the shorter its life time will be.
42
How much power output is the sun currently producing?
4 x 10^26W
43
What will happen to a star 1.4 times the mass of the sun at the end of its hydrogen fusion phase?
It will kove off the main sequence anf first become a red giant before becoming a white dwarf.
44
When will a low-mass star become a red giant?
When most of the hydrogen nuclei present in the core have been fused to helium. Nuclear fusion will stop.
This means the radiation pressure acting oiutwards will also stop and the star will experince an inwards force due to gravitational attraction.
45
Describe the formation of a rad giant after fusion in the core of a main sequence star has stoppped.
The ner inwards force, causes the core to contract, leading to an increase of temperature as it compresses. There is still a large quantity of hydrogen gas surrounding the core. The core releases thermal energy. These outer layers expand to cover a greater volume than the original sta, cooling and leading to the formation of a red giant.
46
After the production of a red giant, and the star continues to collapse, what happens?
The core become hot enough for fusion to begin again, leading to heavier elements, inculding carbon and oxygen.
47
What is produced during the production of carbon and oxygen in the core of a red giant?
Enormous amounts of energy is released, increasing the outwards radiation pressure.
48
What happens once the fusion the the core of a red giant stops?
The star becomes unstable and begins to collase again. At this stage, the outer layers may be ejected back into space forming a plantary nebula while the rest of the star continues to collapse under ity's own mass until it reaches a point where it can collapse no further,
49
What is produced when an unstable red giant can no longer collapse any further?
What is left is very hit, dense core called a whitye dwarf. No further fusion takes place but the star continues to radiate energy as the photons produced from past fusion leaks away.
Eventually, the white dwarf will gradually coll down with a surface tem erature of just a few kelvin.
50
What will a high-mass star beome after its main sequence star?
A beutron star, or a black hole, or a supernova.
51
What is a contiumous spectrum?
A spectrum that appears to contain all wavelengths over a wide a comparatively wide range.
52
Define energy levels of an atom?
Energy levels insode an atom are the specific energies that electrons can have when occupying specific orbits. Electrons can only occupy these discreet energy levels and cannit exist at other values between them.
53
What is the emission line spectum?
The emission line spectrum of an element is the spectrum of frequencies of electromagnetic radiation emitted due to electron transitions from a higher energy level to a lower one within an atom of that element. Since there are many possible electron transitions for each atom, there are many different radiated wavelengths. A line spectum consists of a series of bright lines agains dark lines.
54
What is an absorbtion line spectrum?
An absorbtion line spectum is the pattern of dark lines in a continuous spectrum from a lihht source and is caused by light passing through an absorbing madium such as gas. The dark lines represent the wavelengths that are being absorbed.
55
What is transmission diffracting grating?
A transmission diffracting grating is a glass surface having a large number of fine parallel grooves or slits, and is used to produce optical spectra by diffraction of transmitting light.
56
What is a maxima?
Maxima are reigions of brightness whuch will be seen when the pth difference between overlapping waves is equal to a whole number of wavelengths.
57
What did Joseph von Fraunhofer discover on the suns spectum?
He discovered dark lines on the suns spectrum where frequencies were missing.
58
What properties did Niels Bohr propose atoms have that explained the existance of spectra lines?
* Electrons orbit the nucleus.
* The electrons can occupy certain orbits. These orbits are associated with definite energies and are also called energy levels.
* Electrons loose or gain energy by moving from one allowed energy level to another, absorbing or emitting elecromagnetic radiation with a frequency determined by the energy difference of the energy difference of the levels according to Plank relation for the photons energy.
59
How can an electron be described if it moved from a lower energy level to a higher one?
It's said the electron is excited.
60
When will an electron move from a lower energy level to a higher one in an atom?
Tis happens is a gas absorbs energy from the suroundings, for example, if it's heated.
61
What is the energy required to move the electron to the higher energy level equal to?
The energy required to move an electron to a higher energy level is equal to the energy difference between the 2 levels.
62
What is emitted when an electron falls to a lower energy level in an atom?
Elecromagnetic radiation of a fixed energy and wavelength.
63
When is an electrins energy 0 in regards to it's distance from the nucleus?
When it ois a long way from the atoms nucleus.
(Similar to how we define gravitational potential as 0 at infinity)
64
What happens to the engery of an electron when it moves closer to the nucleus of an atom?
As an electron moves towards the nucleus from very far away, its energy decreases below 0 so energy levels inside an atom have negative values.
65
How can an electron in it's lowest energy level be described?
When an elecrtron is at it's lowest energy level, we say this is ground state.
66
What is ground state equal to in a hydrogen atom?
-13.6eV
67
A hydrogen atom has a ground state of -13.6eV, what does this mean for an electron?
If means an electron would need to be supplied with energy equal to 13.6eV to remove it completly from the atom.
68
What is removing an electrom from an atom called?
Ionisation
69
When is an emission line spectrum produced?
When an excited electron in an atom moves from a higher to a lower energy level and emits a photon with an energy correponding to the difference between these energy levels.
70
In regards to electron movind to different energy levels, what can hot gases produce?
Hot gases produce emission line spectra.
71
What doo the lines on an emission line spectra corespond to?
The lines correspond to a different energy level transition within the atom. Each element's emission line spectrum is unique and acts as a fingure print for the element.
72
Describe the emission of light from stars.
Fusion reactions in a stars core produces photons of elecromagnetic radiation which move upwards through the layers of gas surrounding the core. The photons are constantly absorbed by atoms in these gases, which them re-emit photons of many differernt frequencies in different dirrections.
73
What sort of wavelengths are there from light from a star? Why?
The electromagnetic radiation coming from a star;s inner reigion is a continous spectrum of wavelengths, from radio to gamma rays, due to photons being absored and re-emitted by layers of gas surrounding a stars core.
74
Is the suns atmosphere hot enough to produce emission lines?
No
75
What is an absorbtion line spectrum?
When an atom in a gas absorbes a photon of the correct energy, an elecron moves from a lower energy level to a higher one. The particular wavelengths of light corresponding to these transitions are then missing from the continous spectrum.
76
What is an absorbtion line spectrum?
When an atom in a gas absorbes a photon of the correct energy, an elecron moves from a lower energy level to a higher one. The particular wavelengths of light corresponding to these transitions are then missing from the continous spectrum.
77
Why does each element produce a unique pattern of spectra lines?
It's due to the fixed energy levels in atoms of that element.
78
What can the presence of spectra lines in a stars absorbtion line spectrum be used for?
To identify elemenys within stars.
79
How can visible light be separating in to a spectrum?
Either by a prism or a transmission diffraction grating.
80
Why is transmission diffratction grating essential to analyse the wavelngths of a star compared to using a prism so separate the inght into a spectrum?
With transimssion diffraction grating, the angular dispersion or separation of colours is much greater, allowing more accurate measurements.
81
What determines the angle light is diffracted at after being transmitted through multiple slits of a grating?
The wavelength of the incident light and the separation of the slits.
82
What would the diffraction of monochrome light look like?
Each maximum is a single line of that colour.
83
What would the diffraction on light with a spectrum of wavelengths look like?
Each wavelength interferes separetly so each maxima is a spectrum.
84
What equation can be used to detetrmine tye wavelength of light when diffrected?
nλ = d sin θ
* Where n is the order of the maxima.
* d is the separation of the slits in the grating.
* θ is the angle that the beam makes with the grating.
85
What is Wien's displacement law?
Wien's displacement law states that λmax α 1/T ot T=constant (2.89 x10-3mK). This is used to estimate the peak surface temperaature of a star from the wavelength at which the star's brightness is maximum.
86
What is Stefan's law?
Strfan's law relates the luminocity L of a star with its absolute temperature T: L = 4πr^2σ^2T^4, Where σ is Stefan's constant and has a value of 5.67 x 10-8 Wm^-2k^-4.
86
What is Stefan's law?
Strfan's law relates the luminocity L of a star with its absolute temperature T: L = 4πr^2σ^2T^4, Where σ is Stefan's constant and has a value of 5.67 x 10-8 Wm^-2k^-4.
87
What does the wavelength of elecromagnetic raditaion emitted by an object depend on?
It's temperature.
88
Wavelength of emitting electromagnetic radiation changes with temperature, use this to decribe what you can see when a grill is turned on.
When a grill is turned on, it begins to heat up, and we feel the energy transferred in the from of inrared radiation. A few miuntes later, the grill will glow a dull red colour, then an orange colour. Eventually, if left on for long enough, it will become white-hot as all of the wavelengths of visable light are emitted.
89
What does the position of the peak pof a star depend on?
Its temperature.
90
On one of these diagrams, at lower temperatures, how is the peak affected?
At lower temperatures, the peak is shifted to the right and corresponds to a higher value of the wavelength on the x-axis.
91
On one of these diagrams, as surface temperature increases, how is the position of the peak affected?
The peak moves to the left. As temperature increases, the area under the curve also increases.
92
As temperature increases, the area under a curve on this diagram will increase. Why is this true?
The area under the curve represents the total energy emitted by the body and this is strongly-tempertaure dependant.
93
What does the peak in this diagram represent?
It represents the wavelength that corresponds to the peak intensity of power of the stars emission. (λmax)
94
What is the relationship between the value of λmax and the absolute temperature of the stars surface?
λmax α 1//T or T=constant (2.89x10^-3mK)
(Wien's displacement law)
95
What is Wien's displacement law used for?
Used to estimate the peak surface temperature of a star from the star's spectrum.
96
Wien's law is an empirical law, what does this mean?
This means it was based on available data and not on any scientific theory or hypothesis.
97
Where does the xplanation of Wien's law come from?
The explanation comes from the facts stars behave as if they were a perfect black body- this means the stars emit radiation with a characteristic curve shape that depends on it's temperature.
98
Define the luminocity of a star.
The luminocity of a star is the total energy tht the star emits per second, or the power.
99
What is a star's luminocity related to?
Its temperature and surface area.
100
What is a stars luminocity proportial to?
The luminocity is proportional to the fourth power of the stars surface temperature. (LαT^4) and is directly proportional to the surface area (L α πr^2), leading to Stefans law.
101
What does each bit of the equation represent: L = 4πr^2σ^2T^4?
* L= luminocity
* r= star's radium
* σ= Stepha's constant
102
AS energy spreads out from a star, how does it's intensity change?
As the energy spreads out from the surface of the star, the area over ehich it spreads increases and so the intenisity decreases as an inverse square law.
103
What are some problems when using Wien's displacement and Stefan's law meaning there is difficulties obtaining highly accurate results?
* The eart's atomsphere, which only allows certain waveleangths of electromagnetic radiation to reach us. Dust and human lighh pollution also affect the data we collect, which is why astonomers place telescopes at high altitudes, and on spacecrafts orbiting the earth.
* Detectors are often wavelength-sensitive. Some detectors do not respond to some wavelengths, which could provide inaccurate values for λmax of a star which radiates mainly in that wavelength region.
104
What is the astronomical unit (AU)?
It is the mean distance from the centre of the Earth to the centre of the sun.
105
What is a parsec?
The parsec is a unit of ditance that gives a parallax angle of 1 second of arc (1/3600 of degrees), using the radius of the earth's orbit (1 AU) as the baseline of a right-angles triangle, one parsec is aproximetly equal to 3.1x10^16m.
106
How can you calculate one parsec?
107
What is stella parallax?
Stella parallax is the apparent shifting in position of a star viewed against a background of distant stars when viewed from different positions of the earth, such as different positions of the earth's oorbit around the sun.
108
Define a light year.
The light year is the distance travelled by light in one year in a vacuum. Aproxximatly 9.5 x 10^15m.
109
Is the astronomical unit cocnstant?
It is an average of the distance between the centre of the sun and the centre of the earth due to earth havig an eliptical orbit.
110
What is the priciple of parallax based on?
It's based on how the position of an object appears to change depending on where it is viewed from.
111
What is aparallax error?
A parallax error is the apparent shift in an object's position as it is viewed from different angles.
112
When will a star be 1 persec away from the earth?
When the angle of the parallax subtended by the radius of the earth's orbit is 1 arc second or 1/3600 of a degree.
113
What is parsecs used/ to measure?
The distance between the earth and stars or neibouring galaxies.
114
At the scale of a solar system, why is using a parsec innapropriate?
It is too large, over 20,000 times greater than the size of an astronomical unit.
115
Why are stella parallax measurements limited to nearest stars?
Earth's orbit is so small compared to the distances to stars that even the nearest stars have very small angles of parallax / apparent changes in position.
116
What is the Doppler effect?
It is the shift in wavelength caused by ht e relative motion between the wave source and aan observer. For elecromagnetic radiation or frequency and wavelength, the dopler equation is Δλ/λ ≈ Δf/f ≈ v/c.
117
What is the red shift?
The red shift id the apparent increase in wavelength of elecromagnetic ratiation caused when the source is moving away, relative to the ibserevr.
118
What is the colour reds wavelength like compared to the colur blues wavelength.
Red has a longer wavlength compared to blue with a shorter wavelength.
119
What is hubble's law?
Hubbles law states the the recessional velocity of a galaxy is directly proportional to it's distance from earth.
120
What is HUbble's constant?
It is the constant of proportionality in the euation v= H0d.
121
When can we experience the doppler effect in everyday life?
When a siren travells towards us, we hear the sound at a higher pitvh compared to when it is travelling away. This is because, when they are travelling toowards us, the wavelength will be shorter compared to when it is travelling away, which will appear at a hiigher pitch.
122
How can the Doppler effect be seen in starts?
The Doppler effect can also be seen in elecromagnetic waves, When a star is moving towards u, it appears blue as the wavelength is shorter, however, when it is moving away, it appears red beacuse the wavelength is longer.
123
How can spectral lines taken from an emission line spectrum be used to tell if a star is moving closer or further away?
If stars are travelling away from us, their sprecta lines will shift to the right, towards the red end of the spectrum. The opposite happens for the blue shift is a star is travelling closer.
124
How did Edwin Hubble show that the universe was expanding?
His evidence came from examining absorbtion line specra lines from a number of galaxies. He noticed that the line were shifted towards the red end of the spectrum as the light being received from these galaxies with being 'stretched'- meaning they were moving away from us.
125
Will galaxies closer or further away be travelling further away from us faster or slower compared to ones closer?
They will be travelling away from us faster.
126
Why is it difficult to be certain how accurate the value for the Hubble constant is for different galaxies?
Due to the random and systematic errors involved in calculating the distance to a star. Also accuracy is impeded by the fact the relative motion mat not be along the line of sight between source and observer (nearby galaxies are rotating).
127
What is this graph?
Hubble's original graph of recessional velocity against distance shows a linear relationship, but with many points large distance from the line of best fit. More recent data for many more gaxies has less scatter.
128
What are the units for Hubble's constant?
Km per megaparsec.
129
How can we find the time since the Big Bang for the galaxy?
By dividing distance by speed of ressession.
130
What must we assume is constant if we are finding the time since the Big Bang of the galaxy?
Assume the speed of recession jas been constant over history.
131
What is cosmic microwave background radition?
This is microwave radiation recieved all over the sky orginating from after the Big Bang, when the universe cooled to near a temperature 3000K. As the universe has expanded this radiatoion is now just a faint microwave glow with a preak wavelength coresponding to temperature of 2.7K.
132
Define the Big Bang.
The teory that the universe wqas created from a single point where all the universe's current mass was situated. At the time of creation, the universe was much smalled, hotter and denser than it is now.
133
What was created during the Big Bang?
Time and space.
134
What is the cosmological principle?
This states that on a large scale the universe is isotrphic (the same in all directions) and homogenous (of uniform density as long as a large enough volume is considered).
135
In ancient times, what did people belive about the structure of the universe?
The Earth was the centre of the universe and the sun, moon and stars all revolved around it.
136
Who discovered cosmic microwave background radiation?
Bob wilson and Arno Penzias.
137
How did Wilson and Penzias accidently discover cosmic micrfowave background radiation?
They were studying radiation from hot, energetic electrons ina cloud of gas in the nearby milky way, however, noticed that their radio temescope detected unwanted sinal in all directons- this was cosmic microwave background radiation.
138
How did they discover the temperature of the uncover was 2.7K?
They measured cosmic background radiation having a peak intensity as 0.011m, which from this they could found the universe to be 2.7K.
139
How did Wilson and Penzias's discovery provide evidenmce for the Big Bang?
The Big Bang states it started in an explosion due to high temperatures, eneretic photons would have filled the early universe, initally into the form of gamma ray photons decoupled from matter after 300 000 years after the Big Bang. They calculated from the universe expanding andf cooling, the background radiation today would just be a few kelvin- which Wilso and Penzias predicited the right temperature.
140
What does the comsological principle state?
The universe is:
* Isptrophic- the same in all directions.
* Homogenous- uniform in density.
* Subject everywhere to the physical laws and models that apply here on earth- that the laws og physics are universal.
141
What does it mean that the universe id isotrophic?
The iniverse is the same in all directions- although the universe does not have the same density at every point dur to plantes, stars and areas of enpty space, over the whole volume of space, the distribution of matter does seem uniform.
142
What does it mean that the universe is homogenous?
The universe has uniform density. Althgough in the universe there are areas were there is greater amounbts of matter, over a large enough volume the density of the universe is uniform.
143
The universe is isotrophic and homogenous, what does this provide evidence for?
This provides evidence for the cosological principle and that states that the laws of physics are unchanging through the universe.
144
How did Wilson and Penzias know that they had detected came from everywhere in the universe, and wasn't just background noise?
The signal could not be background noise because the same signal level was always detected in any direction
and the signal did not vary with time. This meant the signal could not be coming from a radio source on Earth or
the Sun and Solar System (which would be an anisotropic signal).
145
How can wavelength of elecromagnetic radiation have temoerature associated with it?
All objects emit radiation with a range of wavelengths, and the spectrum of wavelengths has a characteristic
curve shape that depends on its temperature. It is the wavelength of the peak of the spectrum (maximum intensity) that is related to the object’s temperature.
146
Why is tghe value of 2.7K so important? What would it have been if the universe was younger?
The microwave background provides evidence of thermal radiation (photons moving about randomly in space)
everywhere in the Universe and (due to redshift by the expansion of the Universe) the very early Universe had
very high temperatures. Hence the Universe had a beginning (a Big Bang). The value of 2.7 K together with the
rate of Hubble expansion tells us the age of the Universe by extrapolating the ‘cooling time’ back to the Big
Bang. If the Universe was younger, the microwave background temperature would be higher.
147
Why did state theorist change their theories to acommodate matter being produced between galacies after work by Wilson and Penzias?
In a steady state Universe, there would be no microwave background radiation as there is no hot beginning to the
Universe. When the microwave background was discovered, the steady state theory was shown to be invalid and
so a modified steady state theory was proposed to account for the origin of the microwave background radiation.
Small creation events (mini Big Bangs) between galaxies would be a source of microwave radiation.
148
The light from most galaxies are red-shifted. The further the galaxies are away from earth, the more the light is red-shifted and the faster they're moving away from us. What does this provide evidemce for?
Provides eveidence that thje universe is expanding.
149
What happened 10^-34s after the Big Bang?
Temoeratrure > 10^22. Scientists canniot determine what the universe was likle at this point. The tool of science will never allow us to find out. It is possible that the universe was infinetly dense, infentely hot and infinietly small.
150
What happened between 10^-43s - 10^-34 seconds after the Big Bang?
Aperiod called inflantion which is the fastest rate of expansion ever. The universe went from the size of an atom to the size of a grapefruit.
151
What happened between 10^-32 to 10^-6 after the Big Bang?
Matter is formed- quarks, leptons and photons, however cannot form heavier perticles like protons and neutrons due to the high temperatures.
Slightly more matter than antimatter in the universe.
152
What happened 10^-4s after the Big Bang?
* The universe is now cooled enough for quarks to join together to form protons and neutrons, but there are no atoms .
* Matter and antimatter continue to collide and annihilate, resulting in enourmous quantities of high energy photons- these interact with charged particles so photons are continually absorbed and re-emitted.
153
What happened 100s after the Big Bang?
Temperature of the star has cooled and now behaves in the same way as the core of a star. Helium and lithium nuclei start to be formed but temperature is too low for other fusion to occur. Matter is in plasma form- protons and electrons are not bound to one another as temperaturre is too high.
154
What happened 250 000 years after the Big Bang?
* Temperature is now low enough for hydrogen and helium atoms to be formed as elecrtrons can combine with electrons.
* The photons that existed at this time become microwave background we detect today.
155
What happened 1 million years after the Bing Bang?
Tiny density fluctuations result in the first large-scale structure of the universe- the seeds for galaxies to form.
156
What happened 1 billion years after the Big Bang?
More structures form: heavy elements from s a result of gravitational collapse of stars.
157
What is dark matter?
Matter which cannot be seen and that does not emit or absorb electomagnetic radiation. It is not detected directly , but is indirectly based on its gravitational effects relating to either the rotation of galaxies or by gravitational lensing of starlight.
158
What is dark energy?
A type of enbergy that permeates the whole universe and opposes the attractive force of gravitation between galaxies via the exersion of negative pressure. It is not detected directly, but we know it exists because we know the universe is accelerating as it expands.
159
What would the desity of the universe if the density of it is too great?
The universe will collapse on itself, causing the 'big crunch'.
160
What would the destiny of the universe be if the density of it is too low?
The universe will carry on expanding forever and cool down as it does.
161
What would the desitny of the universe be if the densityis exactly equal to the critical density?
The universe will expand, decreasing in velovity as it does so, it will eventually reacyh a final, finite size after an infinite amount of time.
162
Why is it difficult to determine the fate of the universe?
We must determine the density of the universe, however, not all matter in the iniverse gives out light- dark matter.
163
How do we know that not all the matter in the universe gives out light?
The mass of a star can be estimated by measuring it's luminocity but, the value obtained for the mass of a galazy from it's luminocity does not correspond with the mass of the galaxy predicted from observations of how fast it rotates.
164
How does the difference im mass determined by the luminocity of a galaxy vary with mass deterined from observations with how fast it rotates?
The size of the centripetal acceleration acting on a galaxy, based on the luminous mass, is far too low to account for the galaxy's observed rate of rotation- it must contain more mass we cannot detect.
165
How much of the universe do scientist estimate dark matter makes up?
Around 27%
166
How can we estimate the mass of the universe by considering the centripital acceleration of stars and interstellar matter as it orbits around the galaxy centre?
By equating centripital acceleration, v^2/r, with Newtons law of gravitation, GM/r^2, we can get M=v^2r/G.
Assuming M and G are constant, we can assume as v is proportional to r^-1/2.
167
How can you measure the orbital velocity in spiral galaxies?
By measuring the Doppler shiuft of clouds of ionised hydrogen in different parts of the galaxy.
168
When astimating thr mass of the galaxy, what did they find in terms of it's velocity?
Rubin discovered that the gas clouds in the galazy was moving faster than expected- so gravitational attraction of the visible stars in the galaxy was not enough to hold them in orbit. SInce the orbital velocity did not decrease as expected this was evidence for a massive amount of unseen matter in the galaxy.
169
What is a dark halo?
Dark matter that surrounds individual galaxies.
170
Is dark matter made of protons and neutrons?
no
171
What are the 4 most likely type of particle that makes up dark matter?
* WIMPs
* MACHOs
* Axions
* Neutrinos
172
What eveidence do we have for dark energy?
The acceleration of the universe expanding is increasing.
173
What is dark energy?
Distributed evenly across the universe, an unknown form of energy that opposes athe attractive forces of gravitation bwetween galaxies do drives the accelerated expansion of the universe.
174
What is dark matter?
Located in discreet areas in the universe, it is an unknown form of matter which cannot be seen and does not emit or absorb elecromagnetic radiation.
