Yr 13 - Astrophysics & Cosmology (5.5.1 & 5.5.2)

Question 1

Planet

Answer 1

A large mass
- No fusion
- Orbits a star
- Has cleared its orbit of most objects

Question 2

Galaxy

Answer 2

Huge collection of gas, dust and billions of stars including their planetary systems.

Question 3

Star

Answer 3

Luminous ball of held together by its own gravity.

Question 4

Planetary Satellites

Answer 4

Naturally or man-made bodies that orbit planets

Question 5

Comet

Answer 5

Small irregular balls of dust, ice and rock.
- Highly elliptical orbits

Question 6

Terrestrial Planet

Answer 6

Planet with a hard surface (Rock or Metal).

Question 7

Nuclear fusion

Answer 7

The process of 2 nuclei joining together & releasing energy from a change in binding energy.

Question 8

Binding Energy

Answer 8

Energy required to separate particles.

Question 9

Universe

Answer 9

All of space & time and their contents.

Question 10

Gravitational Collapse

Answer 10

Inward movement of material in a star due to the gravitational force caused by its mass.
- Occurs in mature stars when internal gas and radiation pressure can no longer support its mass.

Question 11

Radiation Pressure

Answer 11

Pressure due to the momentum of photons released in fusion reactions.
- Acts outward in direction of energy flow

Question 12

Gas Pressure

Answer 12

Average linear momentum of gas particles.

Question 13

Main Sequence Star

Answer 13

Any star that fits the L - T relationship (L ∝ 1 / T )

Question 14

Red Giant

Answer 14

Star in later stage of its life that has nearly exhausted the hydrogen in its core
- Larger than normal star due to surface layers cooling and expanding.

Question 15

Planetary Nebula

Answer 15

Expanding, glowing shell of ionised hydrogen and helium ejected from a red giant star at the end of its life.

Question 16

Electron degeneracy pressure

Answer 16

Pressure that stops the gravitational collapse of a low-mass star.
- Pressure that prevents a white dwarf star from collapsing.

A quick way to think about this is by imagining a tube of tennis balls, in which each tennis ball represents an electron. The tennis balls can only sit one on top of each other in the tube; there is not enough space in the tube for two tennis balls to be at the same level. If you try and push a tennis ball down onto another tennis ball, there is a resistive force that pushes back upwards. This is (somewhat) similar to the how the electron degeneracy pressure works.

Question 17

Chandrasekhar limit

Answer 17

Maximum possible mass for a stable white dwarf star (1.4 solar masses).

• White dwarfs with greater masses collapse further to become neutron stars or black holes.

Chand - ra - se - kar

Question 18

Red super giant

Answer 18

Star that has exhausted all the hydrogen in its core and has a mass much greater than the sun.

Question 19

Supernova

Answer 19

Huge explosion produced when the core of a red super giant collapses.

Question 20

Neutron star

Answer 20

Remains of the core of a red super giant after it has undergone a supernova explosion.
- Incredibly dense and composed of mostly neutrons.

Question 21

Black Hole

Answer 21

Core of a massive star that has collapsed almost to a point.
- Very dense and small.
- Gravitational field so strong that light cannot escape.
-Escape Velocity greater than speed of light.

Question 22

Escape Velocity

Answer 22

Minimum Velocity an object must have to escape a gravitational field.

Question 23

What does a Hertzsprung-Russell (HR) Diagram show & describe what it looks like & where certain stars will be.

Answer 23

Graph showing the relationship of a stars Luminosity & Temperature.

• Stretched S shape from top left to bottom right
• White Dwarf bottom left
• Red giant just NE of SOL
• Supergiants top right
• SOL midway through S shape
• S shape is main sequence
• Cold to hot on x axis

Question 24

Luminosity

Answer 24

Total energy emitted by a star per second.

Question 25

Protostar / Stellar Nebula

Answer 25

Hot dense sphere of dust & gas that could become a star.

• Not all protostars start nuclear fusion

Question 26

Explain what happens when a star has a mass less than the Chandrasekhar limit

Answer 26

• Moves off Main Sequence
• Becomes Red Giant
• Planetary Nebula
• White Dwarf

Question 27

Explain what happens when a star has a mass more than the Chandrasekhar limit

Answer 27

• Moves of Main Sequence
• Becomes Red Super Giant
• Supernova
• Black Hole or Neutron Star

Question 28

Lifecycle for Large Star

Answer 28

• Stellar Nebula
• Massive Star
• Super Red Giant
• Supernova
• Black Hole OR Neutron Star

Question 29

Lifecycle for average/small star

Answer 29

• Stellar Nebula
• Protostar (nebula comes together into tight mass of hydrogen, gas and dust)
  -Average Star (protons begin nuclear fusion due to high pressure and temp)
• Red Giant
• Planetary Nebula
• White Dwarf

Question 30

Nebula

Answer 30

collection of hydrogen dust and gas

• Comes together due to gravity
• Forms stars

Question 31

Solar System

Answer 31

Collective name for star & all objects orbiting it.

Question 32

what causes the outward & inward force on a star?

Answer 32

Fusion reactions - Outward
Gravity - Inward