Stellar evolution Flashcards
Our galaxy
The Milky Way
A star
A massive, luminous sphere of plasma held together by gravity
How we understand stellar evolution
- because stars evolve over billions of years
- we understand them by observing many different stars
- at different points in their lifetimes
The birth, life and death of stars
Stellar evolution
Gravitational contraction
- The process whereby a nebula’s gravity overcomes its internal pressure
- causing it to collapse
The huge clouds of gas and dust in which stars are born
Nebulae
The young star that starts to form as gravitational collapse takes place and thermal energy increases
A protostar
The reason for increased thermal energy in a protostar
Gravitational potential energy -> kinetic energy -> thermal energy
A process in which atoms combine to create larger atoms and massive amounts of erergy
Nuclear fusion
The main nuclear fusion reaction taking place in young stars
Hydrogen atoms fuse to form helium and energy
Requirements to start nuclear fusion in stars
Massive amounts of heat and pressure
Stars in a state of equilibrium
- 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.
`The temperature scale used in science
Kelvin (K)
The standard unit of mass in astronomy
Solar mass
1 solar mass = the mass of the sun
The region around magnetic material, or a moving electric charge, where the force of magnetism acts
The magnetic field
One of the most visible differences between stars
Their colour
The main colours of stars
- Blue
- White
- Yellow
- Orange
- Red
Blue stars
- Hottest
- Usually younger
- Often larger
Which stars move through stellar evolution the fastest
The larger stars
Smallest and coolest stars
Red dwarf stars
The stellar characteristics of the sun
Roughly halfway through its life cycle
A medium sized yellow dwarf
Surface temperature about 5800 K
The fate of stars like our sun towards the end of their sequence as hydrogen has been depleted
They swell up to form a red giant
How red giants form
- 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
Planetary nebula
- 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
A white dwarf
- The heavier collapsed remains of a star once it has shed its outer layers to form a planetary nebula
- It is very hot
The fate of massive stars at the end of their sequence
- The core of a massive star undergoes a rapid gravitational collapse
- This causes a violent explosion called a supernova
