Topic 9 - Astrophysics

Question 1

Universe

Answer 1

A large collection of billions of galaxies

Question 2

Galaxy

Answer 2

A large collection of billions of stars

Question 3

Comets orbit shape

Answer 3

Highly elliptical

Question 4

Planets orbit shape

Answer 4

Almost circular (slightly elliptical)

Question 5

Moons orbit shape

Answer 5

Almost circular (slightly elliptical)

Question 6

Star classification according to colour

Answer 6

The colour changes from blue to white to yellow to orange, as temperature decreases, with the coolest stars appearing red

Question 7

Star colour vs surface temp

Answer 7

A red star is the coolest (at around 3000 K)
A blue star is the hottest (at around 30,000 K)

Question 8

Absolute magnitude

Answer 8

The brightness of a star at a standard distance (10 parsecs)

Question 9

HR diagram components

Answer 9

white dwarfs (bottom left), main sequence (top left to bottom right), red giants (top right above main sequence), red supergiants (top right above red giants)

REFER TO REAL HR DIAGRAM PICTURE

Question 10

Evolution of stars of similar mass to the Sun

Answer 10

1. Forms from a cloud of dust and gas called a NEBULA
2. Force of gravity pulls the nebula together to form a PROTOSTAR. Temp. ↑ and hydrogen nuclei undergo nuclear fusion to form helium nuclei.
3. MAIN SEQUENCE - outward thermal expansion caused by nuclear fusion balances inwards force of gravity. Period lasts several billion years.
4. RED GIANT - hydrogen in the core runs out so force of gravity is larger than thermal expansion pressure. Energy makes outer layers expand.
5. WHITE DWARF - star becomes unstable and ejects its outer layer of dust and gas, leaving behind a hot, dense solid core

Question 11

Evolution of stars with a mass larger than the Sun

Answer 11

1. Forms from a cloud of dust and gas called a NEBULA
2. Force of gravity pulls the nebula together to form a PROTOSTAR. Temp. ↑ and hydrogen nuclei undergo nuclear fusion to form helium nuclei.
3. MAIN SEQUENCE - outward thermal expansion caused by nuclear fusion balances inwards force of gravity. Period lasts several billion years.
4. RED SUPERGIANT - hydrogen in the core runs out so force due to gravity is larger than thermal expansion pressure. Energy makes outer layers expand.
5. SUPERNOVA - undergoes more fusion to make heavier elements. It expands and contracts several times as the balance shifts between thermal expansion and gravity and then explodes into supernova.
6. NEUTRON STAR or BLACK HOLE - supernova throws outer layers into space, leaving a very dense core called a NEUTRON STAR. If the star is big enough, it will collapse and form a BLACK HOLE.

Question 12

How does CMBR support the Big Bang Theory?

Answer 12

CMBR is the thermal energy left over from the BB. It is everywhere right now, which implies that all parts of the universe were in contact long ago. Wavelength has increased as the universe has expanded.

Question 13

How does redshift support the Big Bang Theory?

Answer 13

The redshift indicates that the universe is expanding outward at an ever increasing rate. Redshift is greatest in the furthest galaxies. If we reverse that (i.e. contract the universe), we can tell that it started from a singularity.

Question 14

Big Bang Theory

Answer 14

14 billion years ago all the matter in the universe was contained in a hot, dense ball of radiation and sub-atomic particles. An expansion took place and small atoms began to form, then larger ones.

Question 15

Doppler Effect

Answer 15

The wavelength of the sound/light will become shorter as it is moving towards you, increasing the frequency (blueshift), and stretched as it is moving away, becoming longer and decreasing the frequency (redshift).

Question 16

Describe the red-shift in light received from galaxies at different distances away from the Earth

Answer 16

The further away a galaxy is the greater its red-shift and hence the faster it is moving away from us