Evolution of Stars Flashcards
Evolution of a Star diagram / flow
Describe how stars are formed.
-Stars are formed from huge clouds of gas and dust called nebulae Found mainly in spiral arms of Galaxy (e.g. Orion’s nebula) -Gas cloud begins to collapse and breaks up into protostars -Rise in temperature and pressure as GPE (gravitational potential Energy) KE (kinetic energy). -Temperature at core reaches 15 million k. Fusion starts -Outward pressure from radiation prevents any further collapseMain sequence star is formed. Star reaches stable size
Describe a stars death
-Star runs out of Hydrogen -No radiation countering gravitational collapse -Star collapses -Temperature rises further -Fusion restarts in a shell surrounding the core which is now rich in helium. -Outer layers of the star expand and cool to form red giant. -Temperatures at core rise to 100 million kelvin -Helium nuclei fuse to form carbon. -Helium is depleted -Red giant looses it’s outer layers in an expanding shell of gas. -Planetary nebula -Core collapses to form White Dwarf. -Cools eventually to brown and then black. -Mass of star affects how star dies -Super giants can form iron through fusion -Supernova! -Then Neutron star or Black Hole
What is a supernova?
-A massive explosion at the end of a supergiant star’s life. (greater than 8 solar masses) -Outer layers blown away at speeds of 5000km/s
What is a Neutron star?
-A remnant of a supernova -Mass of sun collapsed into a sphere of 20km diameter. -Intense gravitational fields cause them to spin. -Emit radio waves from their polar regions (Pulsar)
How can we deduce the chemical composition of a star?
-Each element has it’s own unique set of spectral line wavelengths. -Analysis of starlight can tell us what the star is made of.
How can we deduce the temperature of a star?
The temperature of a star determines it’s colour so spectral analysis can also be used to determine its temperature.
How can we determine the radial velocity of a star?
Analysis of the Doppler shift of spectral lines.
Describe the Harvard classification of Spectral type.
OBAFGKM. O is hottest and M is coolest.
What is a HR diagram?
This is a plot of luminosity against spectral type.
Draw a HR Diagram
Which stars will run out of fuel sooner?
-Massive stars (top left of HR Diagram). -61 Cygni is a low mass star and will spend 100′s of billions of years on the main sequence.
Give evidence for the existence of Neutron stars.
Regular pulsating radio signals from Pulsars.
Give 3 pieces of evidence for the existence of black holes.
- Gravitational lensing. Light bent by black hole’s gravity (click here for demonstration) - Speed of rotation of our galaxy and its size hints that the mass at its centre is great enough to be a black hole. - Charged particles spinning around a Black hole produce x rays which we can detect.
