IB Physics HL Astrophysics Option D.5: Further Cosmology

Describe rotation curves near the galactic centre (2)

Assumes density near centre is constant, so star mass feels force caused by sum mass of closer stars; stars outside orbit radius has no net effect;

Explain the fluctuations in CMB (1)

CMB is absorbed by mass, since the universe is not even, minute fluctuations allow structures;

Explain what is meant by an open universe (3)

Continues to expands forever; density is too low for gravity to slow expansion; density<critical density;

Distinguish between dark matter and dark energy (2)

Dark matter adds to attractive force of gravity acting within galaxies; while dark energy is an explanation for work done to increase rate of expansion;

Explain what is meant by a closed universe (3)

Expansion brought to stop then collapses; density is too high; density>critical density;

Explain what is meant by a flat universe (3)

Gravity slows expansion but takes infinite time to get to rest; perfect density; density=critical density;

Describe the characteristics of our universe (2)

Isotropic (looks the same in every direction); Homogenous (local distribution of galaxies/cluster are in one region which looks the same from any region);

Discuss the theories explaining dark matter (4)

Massive Astronomical Compact Halo Objects; low mass 'failed' stars/high mass planets/blackholes; weakly Interacting Massive Particles, undiscovered particles that we don't know; current theories of gravity are incorrect and fail to take everything into account;

Discuss how we know of the existence of dark energy (2)

Measurements of type 1a supernovae show acceleration of expansion; that counters gravity without explanation;

State the arguments against the international effort and collaboration in astrophysics research (4)

Money can be used on providing food/shelter/healthcare; money can be allocated to saving lives rather than research; better to fund a great deal of small diverse research projects; is the information worth the cost?;

Describe rotation curves far away the galactic centre (4)

Observations show effective density reduced so much stars are considered freely orbiting central masses, ignoring other stars; rotation speeds can be calculated by analysing stars spectra, rotation curves show orbital v against distance; curve is an initial linear increase; then flatlines when far away;

Explain the relationship between the cosmic scale factor and temperature (2)

Stretching of universe stretches wavelength of radiation; the cosmic scale factor is inversely proportional to temperature;

State the arguments for the international effort and collaboration in astrophysics research (4)

Understanding the universe sheds light on questions like: why are we here? is there other intelligent life?; fundamental, interesting, important areas for human kind deserves proper research; fundamental research gives rise to technology that can improve lives; life on Earth is an impossibility in the distant future, so we must be able to travel/colonise new planets;

Explain the evidence for dark matter in light of rotation curves (4)

Velocities should decrease with distance, but don't; meaning mass must increase with distance; forms a halo that attracts baryonic matter gravitationally; no observable radiation/interactions;

State the current and recent observations learnt from astrophysics research (over 9000)

check oxford study guide/internet;;;;;;;;;;;

Describe the effect dark energy has on the graph that depicts the cosmic scale factor against time (2)

for a flat universe there will be an accelerating expansion; instead of approaching maximum; http://www.astro.umd.edu/~mavara/lab9-121/html/friedmannLab_01.png

Describe the history of the universe (8)

http://staff.on.br/jlkm/astron2e/AT_MEDIA/CH27/CHAP27AT/TA01.JPG

Describe the graphs of cosmic scale factor against time for a universe without dark energy (3)

https://physicsmadeeasy.files.wordpress.com/2007/10/scale-factor-v-time.jpg