Stars and Galaxies :Stars and Galaxies Ch 27


Characteristics of Stars :Characteristics of Stars Bodies of gas that give off heat and radiation Vary in size and temperature The Sun is 1,392,000 km in diameter and 5,000 to 6,000 degrees C


Slide 3:Composition and Temperature Spectrometer separates lights into a spectrum, emission (bright line), absorption (dark line) and continuous Dark line can tell chemical composition and temperature, elements same as Earth, H, He, Fe, Na, Ca Red stars coolest, 3000 degrees C


Slide 5:Blue stars hottest up to 50,000o C Yellow stars 5,500o C Actual motion, apparent motion (motion of Earth) westward. Daily, yearly. Circumpolar Stars that can be seen year round over North or South pole Doppler effect Blue shift toward Earth, red shift away


Slide 6:Light year, distance traveled by light, in vacuum, in a year. 9.5 Trillion km. Distance can be determined by parallax, taking the angle from different places Compare true brightness (spectrum) to apparent brightness


Slide 7:Cephid variable stars get brighter and fades in a regular cycle that relates to brightness, longer cycles are brighter Stellar magnitudes 6 billion stars observable with telescope 6000 visible to eye


Slide 8:Hubble can view 1 trillion 2 scales of brightness, observed brightness, and how bright the star would be at a fixed distance Apparent Magnitude How bright the star looks, given a number from –30 to 30, dim stars have higher numbers, 6 is the dimmest that the eye can see. Moon is –12.5


Slide 9:Absolute Magnitude How the star would look from 32.6 light years the sun would be magnitude 5 32.6 light years is 10 parsecs, 1 parsec is 3.26 light years, a parallax of 1 second of arc


H-R Diagram :H-R Diagram


Slide 12:Y axis is brightness, x axis is temperature, 0o Kelvin is –273o C Most stars that are visible fall in a band through the center called main sequence stars Large, cool stars are called giants and super giants Small hot stars are white dwarfs


Stellar Evolution :Stellar Evolution Stars begin as nebula, dark cloud of gas and dust 70% H, 28% He, 2% heavier elements An event, like a star explosion, causes the nebula to condense, as the cloud becomes more dense the gravitational attraction increases


Slide 14:The nebula spins more quickly do to conservation of angular momentum The cloud forms a disk with a center called a proto-star, in the disk the temperature increases due to pressure and increased collisions Over millions of years the temperature rises, at 10,000,000o C nuclear fusion begins


Slide 15:Nuclear Fusion, when atoms join together to form larger atoms, 4 H atoms fuse to make 1 He, and energy is released A nebula can create more than one star, that then orbit one and other. The nebula also can produce planets


Slide 16:Main sequence Star The second and longest stage of a star’s life is the main sequence Energy is generated by fusion, 1 gram of hydrogen converted into helium will power a 100 watt bulb 3000 years Energy is forcing the star out and gravity is pulling it in, so it is stable 5% of hydrogen used in 5 billion years


Slide 17:Giants and Super giants When most of hydrogen is used, the star contract, raising the temperature and He begins to fuse into C, H continues to fuse, so energy is increased and the star expands Cools as it expands 10 times Suns size is a giant 100 times the sun size is a supergiant


Slide 18:White Dwarf Stars When fusion ends, the star enters the dwarf stage, the gases dissipate and gravity collapses the matter, which heat and illuminate the gases (planetary nebula) Shine for billions of years Black dwarf


Slide 19:Novas White dwarfs will sometimes explode, giving off large amounts of light for brief periods A white dwarf can go nova several times We think that the dwarfs orbiting main sequence or giant stars pull in gases which build up and explode


Slide 20:Supernovas Stars that are 10 to 100 times the size of the sun give off explosions 100 time brighter than novas


Slide 21:The higher gravity causes giant stars to fuse carbon into more heavy elements until core is almost all iron, which collapses, explodes and gives off as much energy as was release during a normal stars life time


Slide 22:Neutron stars, after the explosion, the core may collapse into and incredibly dense structure called a neutron star The neutron star is made up of protons and electrons forced together to make neutrons,


Slide 23:Neutron stars spin rapidly, pulsars are Neutron stars that give off two beams of radiation


Slide 25:Black hole Stars that are too massive to form neutron stars form black holes. They are so dense that light cannot escape the gravity, infer presence by the gravitational effects. Center of galaxies? Cygnus


Star Groups :Star Groups Constellations, groups of stars in imagined patterns. Leo, Ursa Minor, Cassiopeia. The brightest star in a constellation is the alpha, the second brightest is the beta etc.


Slide 27:Galaxies Large scale grouping of 100 billion stars, 100,000 light years across, 50 billion to 1 trillion galaxies


Slide 28:Milky Way Our galaxies, spiral galaxy, our sun is 30,000 light years from center


The Big Bang :The Big Bang Most accepted theory of the origin of the universe All the matter in the universe was concentrated into a small space (singularity)


Slide 30:The matter was propelled outward in all directions (19 billion years ago)


Slide 31:The heat was very high, as it cooled and gravity started taking affect matter condensed to stars and planets


Slide 32:Quasars. Quasi-stellar radio source, objects 12 billion light years from Earth, moving at .9 light speed. Give off much more heat than we would expect. Giant black holes?


New Stars, new matter :New Stars, new matter Latest type of stars, more dense than a neutron star, less dense than a black hole Made up of individual quarks