Lecture 22 Flashcards
what are stars
balls of hot gas powered by nuclear fusion whilst on main sequence which is most of their life
when do stars die and what are the options
die when they run out of hydrogen
can puff up and be giant stars
if over 8 solar mass, become supergiants and go supernova
what does a stars mass entirely determine
its lifespan, colour, luminosity and temperature
explain relationship for mass determining colour and temp in stars
massive - hot - blue
low-mass - cool - red
why do massive stars die quickly
the amount of fuel needed is proportional to the mass of the stars so big stars will use up their hydrogen quicker
characteristics of massive stars
live shorter lifes, super bright, very blue
what happens when massive stars (> 8M) die
they go supernovae as they are so heavy they implode upon death
leave behind a neutron star of black hole
what happens when stars under 8M die
they shed outer layers as a planetary nebula
leaving behind a white dwarf
where are stars born
in clusters, can have millions of stars at all masses but only few massive stars
what is the initial mass function
the distribution of stars formed in a stellar population
for every massive star, there are hundreds of smaller ones
what is the outshining effect
since luminosity is related to mass,
a few massive stars will dominate the light (and thus colour) in a collection of stars as they are just so much more luminous
how is colour in stars a measure of age
since massive stars live a short time, when they blow up only redder stars are left
as a stellar population ages, it becomes redder.
globular clusters are old
open clusters are young
what is the mass to light ratio
light from a population is dominated by blue stars whereas the mass is dominated by red stars
the mass to light ration depends on age
young, blue, small mass
old, red, high mass
how can we infer the mass of stars
measuring colour and luminosity
where does galaxy light mainly come from
the stars in the galaxy
young galaxies are forming stars so blue
old galaxies not forming stars so red
(applies to regions in galaxies)
