Topic 9 Cosmology

Question 2

What is cosmology?

Answer 2

The study of the universe as a whole, especially with regard to the theories of its origin, nature, structure and evolution.

Question 3

What is brightness (flux)?

Answer 3

This is the amount of light received from a source. It depends on the amount of light being emitted by the object ( luminosity) as well as the distance to the object.

Question 4

What is luminosity?

Answer 4

This is the amount of power (light) emitted by an object such as a star or galaxy in the form of electromagnetic radiation. It is measured in watts.

Question 5

Flux - luminosity relationship equation

Answer 5

F = L / (4πd^2)

Where d is the distance from us to the object.

Question 6

What is a standard candle?

Answer 6

A source of electromagnetic radiation which has a particular luminosity. An example is the 10th brightest galaxy in a cluster of galaxies.

Question 7

What are absorption lines?

Answer 7

These are lines that occur with within a stars or galaxies spectra due to the absorption of photons of a particular energy by certain atoms in the stars cooler outer atmosphere. This creates peaks (dips) within the stars recorded Spectre allowing you to see what elements are present in the stars atmosphere as well as calculate by how far the spectra is shifted indicating red shift.

Question 8

What is the Doppler effect?

Answer 8

The process by which sound waves or light waves are altered based on the movement of the source of the waves. If the source is moving towards you, the waves are shifted to a higher frequency i.e. a higher pitch sound or towards the blue light and if the source is moving away from you, the waves are shifted to a lower frequency, i.e. a lower pitch or towards the red end of the spectrum.

Question 9

Redshift equation

Answer 9

Redshift, z, is defined as the change in wavelength divided by the wavelength at which the light was emitted.

z = (λobs - λem) / λem

Where λobs is the wavelength recorded on earth and λem is the laboratory value expected.

Question 10

What is the apparent speed of motion?

Answer 10

The apparent speed of motion, ν, is the redshift, z, multiplied by the speed of light, c.

ν = zc

Question 11

What is the Hubble relationship?

Answer 11

This states that the apparent speed, ν, at which a galaxy is receding is equal to the distance,d, to that galaxy multiplied by the Hubble constant, Ho.

ν = Ho * d

Where Ho is not actually a constant but changes constantly as a universe ages.

Question 12

What is a quasar?

Answer 12

This is a point like source of light at the heart of very distant galaxies. They are believed to be supermassive black holes that are swallowing whole stars. Before the stars are engulfed, they are rich apart in form a swirling accretion disc around the black hole. Friction forces within the disc cause it to get immensely hot and radiate huge amounts of radiation making quasars extremely luminous.

Question 13

How can we calculate the age of the universe using the Hubble constant?

Answer 13

The approximate age of the universe in seconds can be calculated by the calculation one divided by the Hubble constant

age of the universe = 1 / Ho

Question 14

What is weins displacement law?

Answer 14

This states that the peak wavelength is inversely proportional to the temperature. The hotter the object the shorter the peak wavelength.

λpeak = 2.9 x 10^3 / T

Where λpeak is peak wavelength, 2.9x10^3 is a constant and T is temperature.

Question 15

Photon energy - wavelength equation.

Answer 15

E = hc / λ

Where E is photon energy, h is planck’s constant (4.14x10^-15 eV s), c is the speed of light and λ is the wavelength.

Question 16

What is cosmic microwave background radiation (CMB)?

Answer 16

The black body radiation that pervades the entire universe. It is a relic of the time when the matter and electromagnetic radiation will last in thermal equilibrium, about 300,000 years after the Big Bang. The current temperature of the CMB is 2.73 Kelvin.

Question 17

what is the Big Bang?

Answer 17

The event believed to mark the origin of space and time. Consequences of the Big Bang include the fact that space is expanding, the temperatures of the universe is falling in the elements or isotopes such as helium, lithium and deuterium have a certain abundances in the universe.

Question 18

What are the four universal interactions?

Answer 18

• electromagnetic interactions are responsible for the forces between electrons and protons and atoms.
• strong interactions provide the very strong forces between quarks inside protons and neutrons. A small residual effect of the strong interactions between quarks allow protons and neutrons to bind together in the nuclei of atoms.
• weak interactions are responsible for processes such as radioactive beta decay, which involve both quarks and leptons, and in which particles transform from one type to another.
• gravitational interactions are a relatively weak force that is responsible for making apples for to the Earth, as well as maintaining planets and orbits around stars and control the expansion rate of the universe. It is negligible in atoms that matters when at aggregate into huge lumps such as planets and stars.

Question 19

What are unifications?

Answer 19

These are ideas that above certain energy levels interactions start to behave in a similar manner.

Electroweak unification - weak and electromagnetic - Higgs boson

grand unification - strong, weak and electromagnetic interactions - x boson

superunification - gravity, strong, weak and electromagnetic interactions - strings and branes (m-theory)

Question 20

What is inflation?

Answer 20

This is a period of extremely rapid faster than light expansion.

One effect is that areas of the universe which used to be close enough to establish thermal equilibrium are now widely separated, thus explaining why CMB is so remarkably uniform in all directions.

Question 21

What is a consequence of inflation?

Answer 21

Small scale quantum fluctuations created by Heisenberg‘s uncertainty principal were stretched out to astrophysical scales, and seeded the formation of the structure we see today (galaxies, clusters, super clusters and the cosmic web).

Question 22

Why are there more protons than neutrons in the universe today?

Answer 22

Equal numbers of protons and neutrons were initially produced in the universe from the up-and-down quarks remaining after annihilation. However, free neutrons decay, and this reduced their number, leading to a universe containing about seven protons for every neutron today.

Question 24

Where are neutrons now?

Answer 24

Most free neutrons were soon bound up within nuclei of deuterium, helium, and lithium. The approximate distribution of mass in the universe is about 25% helium to 75% hydrogen, with a small traces of other nuclei.

Question 25

What happened to electrons and positrons after the Big Bang?

Answer 25

Primordial electrons and positrons underwent mutual annihilation, with the remaining electrons eventually combining with nuclei to form neutral items.

Question 26

When did photons last interact with matter in the universe?

Answer 26

About 300,000 years after the Big Bang, when the temperature was about 3000 Kelvin, the photons produced from the matter antimatter annihilation had their last interactions with the matter of the universe. these photos red shifted by factor of 1000 by the expansion of the universe form the cosmic microwave background radiation that is observed today.

Question 27

What happened after the Big Bang?

Answer 27

As the universe called further, galaxies and stars were able to form under the influence of gravity. Stars process like nuclei into heavier ones with their cause. The more massive stars then undergo supernova explosions, throwing material out into space that may be included in later, generations of stars and planets.

Question 28

What is **critical density**?

Answer 28

The density that corresponds to a flat universe model. A universe with a high density can have a positive curvature, whereas a universe with a low density can have a negative curvature.

Question 29

What is the **open universe** model?

Answer 29

A model of the universe which is infinite in size at all times and continuously expands. In an open universe without dark energy, the actual density is less than the critical density and space has a negative curvature. If dark energy is present, the universe may have the critical density and zero curvature and so be flat but open.

Question 30

What is the **closed universe** model?

Answer 30

Model of the universe in which the density is sufficient to eventually halt the expansion and cause a subsequent collapse into a presumed big crunch. A closed universe is finite in size at all times and has a positive curvature. In a closed universe, the actual density of matter and energy is greater than the critical density.

Question 31

What is the **Big Crunch**?

Answer 31

If we live in a closed universe model eventually gravity would overcome the kinetic energy causing the expansion resulting in the big crunch. The universe would start contracting with galaxies moving closer together and it would look like the reverse of the Big Bang. Atoms with ionise under impact of radiation, then the nuclei would be smashed apart into protons and neutrons and finally the nucleon themselves were disintegrated into their constituent walks. Photos would spontaneously create pairs of particles of Aunty particles into equal amounts of radiation and Matter Again for the universe as the temperature of the contracting universe rose, so the four interactions with each intern become distinguishable as a unifications proceed in reverse order.

Question 32

What is the **big bounce**?

Answer 32

It is theorised that if we lived in a closed universe where the big crunch could occur that it is part of a cycle of expansions and contractions which would be referred to as the big bounce. 

Question 33

What is **heat death**?

Answer 33

The ultimate fate of an open universe, in which supermassive black holes evaporate around after 10 to the power of 100 years, creating particle anti particle pairs which would eventually annihilate, producing photos which become diluted and caused to even lower energies as the universe expands forever.

Question 34

What is a **critical universe**?

Answer 34

This is where the universe is perfectly balanced between an open and closed universe. The universe would stop expanding in an infinite amount of time when there is an infinite amount of space between all matter. Such a universe would also suffer a heat just like an open universe.

Question 35

What is **dark energy**?

Answer 35

A mysterious form of negative gravity, which constitutes about 69% of the critical density of the universe and is responsible for the acceleration of the expansion of the universe. Einstein introduced the cosmological constant in 1915 into his equation to account for this negative gravity.

Question 36

What is the **Chandrasekhar limit**?

Answer 36

The upper limit for the mass of a white dwarf. For a carbon oxygen white dwarf, it is about 1.4 times the mass of the Sun. If a white dwarf recruit is enough material to exceed this mass, it may undergo a type la supernova explosion and collapse further to form a neutron star.

Question 37

What are the two potential causes of **type la supernova**?

Answer 37

1- they are the result of two white dwarfs smaller than 1.4 solar masses colliding. 2- they could be the result of a binary system where a white dwarf pulls material from a companion star until the white dwarf reaches the critical mass of 1.4 solar masses.

Question 38

What evidence is there that the early universe was decelerating?

Answer 38

The most distant supernova discovered had luminosity higher than predicted. This suggests that in the early universe gravity caused the expansion to accelerate meaning galaxies were closer together together. As the universe expanded than the dark energy increased eventually allowing for the acceleration of the expansion.

Question 39

what is the critical density of the universe comprised of?

Answer 39

69% dark energy 26% non-baryonic dark matter (unknown) 5% baryonic dark matter (protons and neutrons in unformed stars around galaxies) 0.5% luminous matter (stars, planets, galaxies etc.).