19.1+19.2 Objects in the universe, the life cycle of stars Flashcards
what is nebulae?
gigantic clouds of dust and hydrogen gas…. eventually forming stars/ planets
what are planets?
spherical bodies that orbit planets
what are dwarf planets?
a planet that has not cleared its orbit of other objects
what are moons?
spherical bodies that orbit planets
what are asteroids?
small, irregular shaped bodies, made of dust and metal, cicrular orbits around stars
remians of planets
what are comets?
small, irregular shaped bodies made of dust and ice, eccentric orbits around stars
remains of a solar system
what is the solar system?
a system of plannets orbiting a central star
what is a galaxy?
a collection of stars and planets
what s a universe?
all galaxies in their mass and energy
describe the formation of a star
- nebulae form and come together under gravitational force of attraction
- denser regions of nebulae pull in more matter, becoming hotter as GPE->KE
- a protostar forms in the nebula
- if it becomes massive, dense and hot enough, the GF is able to overcome repulsion between the hydrogen nuclei
- nuclear fusion of hydrogen nuclei begins and the protostar becomes a main sequencing star
draw the life cycle of a star:
what is the beginning of all stars lif cycle?
- denser regions in the nebulae form a protostar
- when protostar is hot and dense enough, nuclear fusio begins and it becomes a main sequencing star
- during this phase (GA=RP) so in equillibrium
GA= gravitational attraction, RP= Radial pressure
what then happens to low mass stars?
evetually hydrogen nuclei in core run out
1. rate of fusion decreases, star cools, RP decreases
2. GA>RP, so the star collapses
3. GPE->KE so it heats up again
4. fusion of hydrogen nuclei in the shell beings (Red Giant)
5. this then also runs out (whole process x2)
6. white dwarf
7. black dwarf
what is electron degneracy pressure?
a pressure exerted by the electrons as the star collapses, since electrons are not allowed to occupy same energy levels.
* this new pressure counters to GFA and so no further collapse of the core is possible
what is the chandrasekhar limit?
- limit to mass of core that will be prevented from total collapse of the star due to electron degeneracy pressure
- if mass is more than this this means core will collapse
how much mass the electron pressure can take on
which has a shorter life cycle, high mass or low mass stars?
high mass stars becuase they have more mass–>more GPE–> more KE–>faster rate of fusion–> shorter lifetime
what is the story of high mass stars?
part 1
- eventually hydrogen nuclei in the core run out
- rate of fusion decreases, star cools, RP drops
- GF>RP, star collapses
- GPE–> KE, heats up again
- fusion of helium nuclei in the core beings, star expands
- fusion of hydrogen in th outer shell begins, outershells expand and cool emitting lower red EM waves (Red super giant)
what is the story of a massive star?
part 2
- the star eventually forms and iron core
- the iron nuclei cannot be fused together (iron is lowest energy nucleus)
- star becomes unstable (GAF»RP) becoming a supernova
- outer shell shed
- dense core remains: neutron star/ black hole
what is a neutron star?
composed of neutrons
small volume
very dense
what is a black hole?
GFA is very strong
photons/ lights is unable to escape the gravitational pull
what is the difference betwen transitioning from a white dwarf to a black hole or neutron star?
- neutron star: if mass of remiing core> chandrasekhar limit
- black hole: if mass of remaining core is greater than 3 solar masses, GPE collapse creates a very dense body
summarise the life cycle of a high mass star
summarise the life cycle of a low mass star
