8 Astrophysics

Question 1

Universe

Answer 1

• Large collection of billions of galaxies

Question 2

Galaxy

Answer 2

• Large collection of billions of stars

Question 3

Solar system

Answer 3

• Collection of planets that orbit a star

Question 4

Gravitational field strength

Answer 4

Factors:
- Body mass
- Distance to body

Uses:
- Causes moons to orbit planets
- Causes the planets to orbit the Sun
- Causes artificial satellites to orbit the Earth
- Causes comets to orbit the Sun.

Question 5

Comet

Answer 5

• Ball of dust and frozen gas
• Highly elliptical orbit
• Speeds up as it approaches the sun, slows down as it moves away
• Tail always faces away from the sun

Question 6

Asteroid

Answer 6

• Rocks that orbit the sun

Question 7

Orbital speed

Answer 7

Orbital speed (m/s) = (2 x π x orbital radius) / Time period

Question 8

Star colour temperature

Answer 8

• Blue: 30,000K
• White-blue: 20,000K
• Yellow-white: 10,000K
• Golden: 7000K
• Yellow: 6000K
• Orange: 4000K
• Red: 3000K

Question 9

Small star life cycle

Answer 9

• Nebulae (large collection of dust, gas, and rocks)
• Protostar: gravity will pull particles together. When close enough, Hydrogen fusion starts, releasing energy
• Main Sequence: Attraction and expansion forces balanced
• Red giant: When it runs out of hydrogen it becomes cooler and redder
• White dwarf: Collapses and becomes hot and dense
• Black dwarf: After millions of years, it cools down

Question 10

Large star life cycle

Answer 10

• Nebulae (large collection of dust, gas, and rocks)
• Protostar: gravity will pull particles together. When close enough, Hydrogen fusion starts, releasing energy
• Main Sequence: Attraction and expansion forces balanced
• Red supergiant: When it runs out of hydrogen it becomes cooler and redder
• Supernova: Shrinks and explodes, releasing massive amounts of energy, dust, and gas
• Neutron star/ Black hole: If the star was big enough, a black hole forms, else neutron star forms

Question 11

Absolute magnitude

Answer 11

• The brightness of a start at a standard distance (10 parsecs / 32.6 light years)
• Used to compare star brightness
• The brighter the star, the smaller the absolute magnitude

Question 12

Big bang

Answer 12

• Universe began from a small, hot, and dense region
• A giant explosion caused everything to expand

Evidence:
- Redshift
- CMB radiation

Question 13

Redshift

Answer 13

• As bodies move further away, light emitted has lower frequencies (Doppler effect)
• Lower frequencies correspond to the red end of the visible spectrum
• The further away, the lower the frequency

Change in wavelength (m) / Reference wavelength (m) = Galaxy velocity (m/s) / speed of light (m/s)

Question 14

Cosmic microwave background radiation (CMBR)

Answer 14

• All parts of the universe contain leftover heat radiation at 2.73K
• The radiation is the microwave region, at the start it was high energy gamma
• As the universe expanded, so did the radiation’s wavelength