Stellar structure
energy transport
radiation
convection
conduction
allows energy produced by nuclear reactions and gravitation to be carried to the surface via photons
hot buoyant mass elements carrying excess energy outward while cool elements fall inward
transport heat via collisions between particles
"radiative transport of photons"
path used by photons called " drunken sailor problem" bcs the path followed by the absorbed and re-emitted photons like that followed by someone too inebriated to stand up for long
in massive stars; the dominant method of cooling or stars in advanced burning stages and also plays a central role in events like supernovae associated with the death of massive stars.
metal transport heat
under certain conditions involving very high densities the matter of a star may become what is termed "degenerate"
not important in normal stars, but must also be accounted for if stars contain degenerate matter.
a very efficient method of energy transport because it involves the vertical motion of large packets of gas.
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galactic stellar populations
= a group of stars within the galaxy that resemble each other in spatial distribution, chemical composition or age
not discrete in properties but have a continuum of characteristics that reflect the changes in star formation with time.
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disk
bulge
halo (nimbus@icebow@gloriole)
inhabits the rotating, flattened region in our galaxy
restricted to the rounded central region of the galaxy
inhabits the far outer regions of the galaxy, on long ellipisodal orbits that takes it into the disk and bulge
contains all the gas and young stars
dominated by old stars and a violent core
contains very old stars and globular clusters
rich in heavy element (>helium in periodic elements)
rich in heavy element
tend to be very poor in heavy elements
LARGER THE NUMBER OF SUPERNOVA NEAR A CLOUD, THE RICHER IN HEAVY ELEMENTS IT WILL BECOME
oldest stars in the galaxy since they have the lowest chemical abundance
youngest bcs have the most metal rich
the structure of the milky way (and other spiral galaxies) consists of:
bulge (roughly spherical system of old stars surrounding the nucleus
disk (flat system centered on bulge that contains the spiral arms, with their molecular clouds and young stars)
halo ( large spherical system of old stars containing globular clusters, some isolated stars, and surrounding the whole visible galaxy)
nucleus (small region in the very center that may contain black hole) - called the "GALACTIC CENTRE" for the milky way
dark matter
galactic stellar populations
populations 1
includes younger stars in the disk/plane galaxy;have all be enriched in heavy elements produced in previous generations of stars
populations 2
older stars that tend to lie around the center and in globular clusters, hence have orbits that take them well out of the disk/plane
stars clusters
= group of stars that formed out of the same molecular cloud, and which remains bound together by the mutual gravitational attraction of its components
open clusters
individual stars are easily resolved through a telescope
exp: HYADES and PLEIADES
sometimes called GALACTIC cluster due to their location on the dusty spiral arms on the plane of spiral galaxies.
have a common origin-formed from the same initial giant molecular cloud
loosely bound by gravity
as the cluster rotates around the galaxy it eventually disperses due to gravitational perturbations with other objects in the galaxy
usually relatively young objects
range from a couple to 20 / so parsecs accross
globular clusters
contain several thousand to one million stars in spherical, gravitationally-bound system.
located mostly in halo surrounding the galactic plane they comprise the oldest stars in the galaxy
these populations 2 are highly evolved but with low metallicites
normally remain gravitationally coherent throughout their lives
prominent examples include 47 TUC, M4 and OMEGA CENTAURI
important of stars clusters
allow astronomers to check models of stellar evolution and the ages of stars.
all stars within a cluster are effectively at the same distance from an observer on earth
the stars that appear brightest within a cluster are intrinsically more luminous than fainter members
