chapter 17 Flashcards
hydrogen is converted to helium in the presence of carbon
CNO cycle
- hydrogen-1 + carbon-12 → nitrogen-13
- nitrogen-13 → neutron → carbon-13
- 2 hydrogen nuclei + carbon-13 → nitrogen-14→ oxygen-15
- oxygen proton → neutron → nitrogen-15 + proton → ejection of helium-4 → carbon-12
CNO cycle chain
begins when a high-mass star runs out of helium, and produces more massive elements
carbon fusion
a region on the H-R diagram containing stars that pulsate with a periodic variating in luminosity
instability strip
- a variable star that undergoes periodic radial pulsations
- most are cepheid variables
pulsating variable star/ variable star (2)
- the relationship between the period of the variability of a pulsating star and the luminosity of the star
- longer period pulsating variable stars are more luminous than shorter-period ones
period-luminosity relationship (2)
- observe the period of the cepheid star
- combine the period-luminosity relationship to find the luminosity
- combined that luminosity with its observed brightness to find the distance
3 steps for finding the distance to a cepheid star
a variable giant star whose regularly timed pulsations are good predictions of its luminosity; less luminous than cepheid stars
RR lyrae variable
hot, luminous, extremely rare stars that are as massive as 150 SM
luminous blue variables (LBV)
the energy required to break the nucleus into its constituent parts
binding energy
thermal energy is carried out of the center of the star by neutrinos rather than by electromagnetic radiation (light)
neutrino cooling
- an atomic nucleus absorbs an energetic gamma ray and emits some particles
- absorbs thermal energy and reverses the results of nuclear fusion
photodisentigration (2)
electrons are absorbed by protons in atomic nuclei, forming neutrons and releasing neutrinos
charged destruction
a supernova explosion where the degenerate core of an evolved massive star suddenly collapses & rebounds
type II supernovae
- the formation of low-mass nuclei during the first few minutes after the Big Bang
- responsible for the creation of massive elements in the universe
nucleosynthesis (2)
an atomic nucleus forms a heavier nucleus after colliding with a neutron and creates heavier elements
neutron capture
a helium nucleus is captured by another nucleus during nucleosynthesis
helium capture
- the neutron-degenerate stellar core left behind by a type II supernova
- has a radius of 10-15 km
- density is ~ 10^18 kg/m cubed
neutron star
- a rapidly rotating neutron star that beams radiation into space n 2 search-light beams
- strong magnetosphere
pulsar (2)
a binary system where the mass from an evolving star spills over onto a neutron star
x-ray binary
bursts of gamma rays lasting a few miliseconds-minutes that originates from a neutron star merging
short gamma-ray burst
- an expanding cloud of debris from the explosion which occupies that place in the sky
- glowing gas expanding away from the central star 1500 km/s
- crab pulsar at the center of the nebula flashes 60 times each second
crab nebula (3)
a spherically symmetric, highly condensed group of stars, containing tens of thousands to millions of members
global clusters
a loosely bound group of dozen to thousand stars that formed together in the disk of a spiral galaxy
open clusters
- astronomers use main-sequence fitting to determine the distance to a cluster
- all the stars in a given cluster are approximately the same distance from earth
- astronomers use clusters to study stellar evolution
cluster distances & ages (3)
- the location of the most massive star that remains on the main-sequence
- indicates the age if the cluster
main sequence turnoff (2)
more reddish stars in its cluster
old clusters
more luminous, bluer stars in its cluster
young clusters
a group of stars with similar ages chemical composition, and dynamic properties
stellar population
