3.4: Evolution Of Stars Flashcards
How are stars formed
By the gravitational collapse of huge clouds of gas and dust found in spiral arms of galaxies. Once gas clouds begins to collapse it breaks up into smaller collapsing knots Calle protostars.these rise in temp as gravitational potential energy is connected to kinetic energy.eventually protostar central temp reaches 15 million k, hot enough for nuclear fusion of hydrogen nuclei to helium to begin.one this occurs the outward pressure from radiation generated in the Stars core halts any further collapse and star settles to stable size.then begins to radiate energy from hot surface and becomes main sequence star
Describe a stars death
Eventually hydrogen fuelling stars core runs out . The outward radiation pressure is now no longer present and star collapses once more under its own gravity, causing further temp rise within star until hydrogen can undergo fusion i. A shell surrounding the core which now rich in helium.new nuclear reactions which occur cause outer layers of star to expand and cool to form a red giant or supergiant.with further hydrogen depletion and contraction temperature at centre of red giant can rise to 100 million k, hot enough for helium nuclei to fuse to form carbon.when this helium is depleted red giant loses outer layers I am expanding shell of gas. This is called a planetary nebula.the inner part of star collapses to form dense hot white dwarf star.eventually white dwarf stars cool to become red, brown and eventually black dwarfs.in larger-mass supergiant star temp of core is hot enough for further fusion reactions involving nuclei of elements up to iron to occur.once these depleted explosion occurs at outer part of core and the supergiant blows away its outer layers.remaining dense core called a supernova and this can be either a neutron star or black hole
What can the stellar spectrum be used for
For deducing a stars temperature and the possible radial velocity of a star by using the Doppler effect
What do astronomer use the relative numbers and wavelengths if spectral lines
To classify stats interns of their spectral type
What is the most common classification scheme for a stars spectral type
The Harvard scheme
O B A F G K M
Oh Be A Fine Guy Kiss Me
O stars are hottest and M stars are coolest
What is the H-R diagram
A chart showing some of the many properties of stars
On a H-R diagram what is the ‘correlation’
Negative
On a H-R diagram what is on the vertical axis
Luminosity
On a H-R diagram what is on the horizontal axis
Spectral type / ‘surface’ temperature
What are the 4 distinct groups on a H-R diagram
- normal main sequence stars like the sun
- red giants
- supergiants
- white dwarfs
What spectral type of star is our sun
G2
Where are white dwarfs located Ina H-R diagram
Bottom left
Where are red giants located on a H-R diagram
Top right
Where are supergiants located Ina H-R diagram
Top
What does the position of a ‘normal’ main sequence star depend on in a H-R diagram
It’s mass
