AST EXAM 3

2 X 10³⁰kg

radius= 700,000 km

6,000 K

3.8 X 10²⁶ Watts

10 trillion yrs

• Convection zone: energy generated in the solar core travel up, transported by the rising of hot gas and falling of cool gas
• Radiation zone: 1/3 way to center; energy moves outward primarily in the form of photons of light
• Core: source of sun's energy; nuclear fusion transforming hydrogen into helium

• the high temperature and pressure allow for fusion of hydrogen into helium
• The proton proton chain: 2 protons fuse and release a positron and neutrino(occurs twice in reaction)->1p 1n; this fuses to a proton(occurs 2X)->2p 1n; these two nuclei fuse and release 2 protons->2p 2n

• a state of balance in which the force of gravity pulling inward is precisely counteracted by pressure pushing out
• ex) acrobat stack

• color
• apparent brightness
• those close enough, distance via parallax

• describes a stars apparent brightness
• *a larger apparent mag means a dimmer apparent brightness

• describes a stars luminosity
• 1 mag = 2.512

• the total amount of pwr a star emits into space at all wavelength's
• direct means= color, brightness, distance

• how bright the stars look in our sky
• need to know luminosity and distance

• used to find distaces for "near" stars
• a star's distance= precise amount fo the star's annual shift due to parallax
• looking at an object from two different directions

• Sys. in which 2 stars continually orbit one another
• To find mass, need orbital period and the seperation of the 2 stars
• Visual Binary: both stars can be resolved through a telescope (observe orbit to find orbital period)
• Eclipsing Binary: 2 stars happen to be orbitting in the plane of ourline of sight, so that each star will periodically eclipse the other(measure time btwn eclipses to measure orbital period)
• Spectroscopic Binary: who binary nature is revealed b/c we detect the spectral lines of one or both stars alternately (measure time it takes the spectral lines to switch back and forth to find orbital period)

• O: dark blue, > 30,000K
• B: blue, 30,000-10,000K
• A: white, 10,000-7,500
• F: dull white, 7,500-6,000K
• G: yellowish, 6,000-5,000K
• K: orange, 5,000-3,500K
• M: red, <3,500K
• The spectral type consists of a letter and a #

• ^ I- supergiants
• | II- bright giants
• | III- giants
• | IV- subgiants
• | V- main-sequence stars

• A Hertzsprung-Russell Diagram
• Def: a graph plotting individual stars as points, with stellar luminosity on the vertical axis and surface temp on the horizontal

• 1) all the stars in a cluster lie at about the same distance from earth
• 2) all stars in a cluster formed at the same time
• Open Clusters: several thousand stars; found in the disks of galaxies and contain young stars; don't last long
• Globular Clusters: million+ stars; found in halos of galaxies(milky way halo); center is packed tight; contain very old stars

• mass governs ALL the star's characteristics
• ex) temp, luminosity, lifetime

Stars form by the gravitational collapse of dense clumps of interstellar dust, gas, and molecules

• inward pull of gravity vs. outward push of pressure(thermal pressure)
• Stars form in molecular cloudsdue to high temps and low densities which gives gravity the upper hand
• when the core starts trapping thermal energy released by gravitational contraction
• pressure begins to push back, contraction slows down and the central part of the cloud becomes a protostar.
• Matter from surrounding cloud build up mass of protostar

• they form in the disk of galaxies
• usually form in open clusters

• Lowest: .08M_sun; anyhting less is called a brown dwarf
• Highest: >150M_sun
• more low mass stars that high mass stars

• Normally, stars can't change mass but can in a binary star sys
• Mass Exchange: A star begins to swell at the end of it's Hydrogen burning life and transfers mass to it's companion

slowly, their luminosity increases

• most of its life, it fuses H->HE via the proton-proton chain
• When H is exhausted, the core begins to shrick while the star itself expands and becomes a red giant
• the HE core becomes hot enough->helium flash that initiates HE fusion
• this causes HE->C = end of life
• core shrinks again
• outer layers expand->thermal pulses and expels outer shell
• the remaining stellar core is a white dwarf
• (have a long life)

• Fuse H->HE via the CNO cycle(cycle of reactions)
• exhaust H core->H shell burning
• ->several stages->burning successively heavier elements
• increase rate of fusion->swell and become a supergiant
• they die during a supernova, scattering newly produced elements
• a supernova occurs when iron is formed in the core->core collapses and explodes=supernova remnant
• leave a neutron star ot a blackhole

• White dwarf: from a low mass star; if it exceed 1.4M_sun, it will explode like a bomb as a white dwarf supernova- due to H acquired through accretion disk
• Neutron Stars: from high mass star; pulsars(rapid pulses of radiation as it rotates) provided the first direct proof for the existance of neutron stars