Galaxy and Universe midterm #2 Flashcards
zero-age main sequence
powered by fusion of H into He. all stars spend 90% of their lifetime on the main sequence
Structural (hydrostatic) equilibrium
stars mass produces inward force of gravity which is balanced by the outward pressure of the gas in the interior of the star.
Globular clusters and open (galactic) clusters
stars that are formed at the same time in the same place and from the same composition
stellar evolution for different masses
lower mass stars evolve a lot slower than higher mass stars. Lower mass stars take billions of years to get off the main sequence where high mass stars only a couple hundred million to get off the main sequence
The main sequence turn-off
the point on the main sequence where stars are just leaving the main sequence
age of the cluster
the main sequence turnoff gives this
low mass stellar evolution
after 5x10^9 years of hydrogen burning into helium there is a helium buildup and the He core collapses to a very small radius (earth) and a very high density
electron degeneracy
dense core finds support from this holding it up by the electrons cannot be pushed any closer together
interstellar dust
dark clouds silhouetted against a bright background. blocks light more blue than red
interstellar extinction
where stars appear fainter
interstellar redenning
stars appear redder
Gas and dust
where the stars are originated
interstellar clouds
dense region where dust and gas congregate
ongoing star formation
H II regions that surround hot luminous o and b stars
Neutral Hydrogen
H I, emits 21 cm radiation at radio wavelengths. used to map the Milky Way galaxy
Molecular clouds
densest interstellar clouds temperature reaches as low as 10K
Carbon Monoxide
used to map clouds
Giant molecular clouds
largest clouds, prime region for star formation
star formation
result in UV radiation from O and B stars that ionize their immediate surroundings
cloud collapses
when their masses are great enough that self-gravity exceeds the outward pressure
collapsing cores
forms separate stars
protostars
the individual cores when collapse is underway
clusters of stars
many protostars are formed at the same time and results in a cluster of stars
Hydrogen fusion
begins when the protostar core becomes hotter until its temperature reaches around 10 million kelvin is when hydrogen fusion begins
surface temperature of protostar
remains constant while collapse is slowly taking place and core is heating up. protostar is shrinking so its surface area is less and the luminosity is decreasing
evolutionary track
the path a protostar or star takes on H-R diagram
accretion disk
material falls onto protostar falls on this disk first then migrates inward
bipolar outflow
protostar is blowing away 2 jets of material vertically perpendicular to the accretion disk
Stellar wind from a protostar
eventually clears away the dust and gas cloud surrounding it and see it as a T Tauri star
Evolutionary timescales of star formation
vary according to mass with the time to H burning being for: 100M - 10,000 years and 10M-100,000years and for 1M- 10,000,000years
Hydrogen Shell burning
Hydrogen is still available in the shell surrounding the collapsed He core and provides the new energy source. luminosity increase and outer regions expand
Helium core burning
He core gets more massive and shrinks more raising the temperature to 10^8K
Helium flash
low mass stars, happens at same time throughout core in only a few minutes. The core temperature increases rapidly from 10^8 to 2x10^8. core expands explosively while the star as a whole shrinks
Triple Alpha process
He^4+He^4>Be^8+He^4>C^12
Horizontal branch or He burning main sequence
occurs after the Helium flash. now burning He in the core and H in the shell. sun will spend 100 million years on this branch
Hydrogen and Helium shell burning
low mass stars never reach core temperatures high enough to burn carbon. When He is exhausted in the core it collapses again
Second red giant branch
H and He burning in separate shells. as they go through this stage they lose large amounts of mass a total of 30-50% of its initial mass being lost
white dwarf
The final result maximum mass of a white dwarf is 1.4. will eventually become a black dwarf
nova
an explosion occurs and part of the outer layer of the star is blown away in 1000km/s.
Type Ia supernovae
if the white dwarf exceeds the 1.4 mass limit collapse occurs and temperature rise to 6x10^8 to ignite C burning. ignites the entire star in 1 second and the star is completely destroyed
Type Ia supernova
large fraction of the star is converted into radioactive iron (Fe) and nickel (Ni) and blasted into space. a luminosity of 10^10 times the sun and outshines the entire galaxy for a time
high mass stellar evolution
stars greater than 8M higher temperatures in the core make additional nuclear reactions possible
CNO cycle
when He burning begins massive star does not go up the red giant branch. moves horizontally across the H-R diagram to the right
final stage of high mass star
no support for iron core so it collapses electron degeneracy occurs but not strong enough to support core. collapse continues.
What does the temperature get to on the final stage of a high mass star
10^10K
What do Gamma rays do in the final stage of high mass stars
break apart Fe nuclei into He nuclei. Electrons are forced into nuclei combine with protons to form neutrons
type II supernova
collapse is very fast. density of core exceeds the density of an atomic nucleus core bounces back and shock wave moves outward. neutrinos are absorbed (about0.2%)
