Stellar evolution

Question 1

Our galaxy

Answer 1

The Milky Way

Question 2

A star

Answer 2

A massive, luminous sphere of plasma held together by gravity

Question 3

How we understand stellar evolution

Answer 3

• because stars evolve over billions of years
• we understand them by observing many different stars
• at different points in their lifetimes

Question 4

The birth, life and death of stars

Answer 4

Stellar evolution

Question 5

Gravitational contraction

Answer 5

• The process whereby a nebula’s gravity overcomes its internal pressure
• causing it to collapse

Question 6

The huge clouds of gas and dust in which stars are born

Answer 6

Nebulae

Question 7

The young star that starts to form as gravitational collapse takes place and thermal energy increases

Answer 7

A protostar

Question 8

The reason for increased thermal energy in a protostar

Answer 8

Gravitational potential energy -> kinetic energy -> thermal energy

Question 9

A process in which atoms combine to create larger atoms and massive amounts of erergy

Answer 9

Nuclear fusion

Question 10

The main nuclear fusion reaction taking place in young stars

Answer 10

Hydrogen atoms fuse to form helium and energy

Question 11

Requirements to start nuclear fusion in stars

Answer 11

Massive amounts of heat and pressure

Question 12

Stars in a state of equilibrium

Answer 12

• Stars that are balanced in their main sequence phase.
• Outwards pressure because of nuclear fusion in the core is balanced with the force of gravity pushing in.
• The star stops contracting.

Question 13

`The temperature scale used in science

Answer 13

Kelvin (K)

Question 14

The standard unit of mass in astronomy

Answer 14

Solar mass

1 solar mass = the mass of the sun

Question 15

The region around magnetic material, or a moving electric charge, where the force of magnetism acts

Answer 15

The magnetic field

Question 16

One of the most visible differences between stars

Answer 16

Their colour

Question 17

The main colours of stars

Answer 17

• Blue
• White
• Yellow
• Orange
• Red

Question 18

Blue stars

Answer 18

• Hottest
• Usually younger
• Often larger

Question 19

Which stars move through stellar evolution the fastest

Answer 19

The larger stars

Question 20

Smallest and coolest stars

Answer 20

Red dwarf stars

Question 21

The stellar characteristics of the sun

Answer 21

Roughly halfway through its life cycle

A medium sized yellow dwarf

Surface temperature about 5800 K

Question 22

The fate of stars like our sun towards the end of their sequence as hydrogen has been depleted

Answer 22

They swell up to form a red giant

Question 23

How red giants form

Answer 23

• Hydrogen fuel runs out for fusion in the core
• Less outward pressure from nuclear fusion
• Stars begin to contract and collapses due to the force of gravity
• Temperature and pressure in the centre increase and fusion of heavier elements begins
• Remaining hydrogen in the outer layers begins to fuse
• The outer layers of the star expand

Question 24

Planetary nebula

Answer 24

• Sometimes a red giant expands to the point that surface temperature drops
• The outside layers of the star are blown away by the radiation (solar winds) coming from below
• The shed material forms the planetary nebula that is lit up by the remaining white dwarf star

Question 25

A white dwarf

Answer 25

* The heavier collapsed remains of a star once it has shed its outer layers to form a planetary nebula * It is very hot

Question 26

The fate of massive stars at the end of their sequence

Answer 26

* The core of a massive star undergoes a rapid gravitational collapse * This causes a violent explosion called a supernova