Quick Quizlet. Quizlettino. Cosmology: How the Universe Works

Transcription

1 Quick Quizlet Which is not thought to be associated with a supernova? a. pulsar b. neutron star c. white dwarf d. creation of heavy elements e. black hole Quizlettino In which is fusion thought to be occurring? black hole white dwarf protostar red giant neutron star Cosmology: How the Universe Works Measuring Astronomical Distances Galaxies The Expanding Universe Background Microwave Radiation The Big Bang Model Measuring Cosmological Distances 1

2 Measuring Astronomical Distances radar ranging triangulation brightness-distance H-R diagrams Cepheid Variable Type 1A supernovae cosmological redshift Distances Star: 10 light yrs Galaxy: 500,000,000 light yrs Locating objects in the sky is easy. Finding their distances is a nightmare! Quasars and stars look identical. But the quasar is much, much farther away. Quasar: 5,000,000,000 light years Brightness-Distance using H-R diagram Also known as Hertzsprung-Russell Method Absolute brightness -- the actual brightness of things viewed from the same distance related to a star s color Apparent brightness -- how bright things look to us here on earth near stars appear brighter than far stars of the same color Distance-brightness with H-R diagram is used for intermediate distances (beyond 100 light years, but need to be able to resolve individual stars) 2

3 Cepheid Variable BrightnessDistance ícepheid variables are stars with brightness that vary over a period of days or months. íbrightness is greater for larger pulsation periods Galaxies GALORE íspiral galaxies (75%) íspiral Milky Way? may be barred íbarred spiral íelliptical (20%) ídwarf ígiant íirregular (<5%) ímagellanic Clouds Spiral Galaxies 3

4 Elliptical and Irregular Galaxies The Expanding Universe íall objects we can see are moving away from us íthe objects at the greatest distance are moving the fastest the Hubble Law. Cosmological Redshift í The Doppler effect causes waves to shift up in frequency as they move towards you and down in frequency as they move away í spectral emission lines have a characteristic pattern í pattern is shifted to the red for distant stars í the amount of shift related to the speed of the star í the speed is proportional to the distance normal spectrum shifted spectrum 4

5 Distance Measurements Summary radar ranging triangulation distance-brightness cosmological redshift within solar system nearest 10,000 stars in galaxy within our galaxy and nearby galaxies beyond nearby galaxies Cosmic Microwave Background Corresponds to a temperature of K Slight irregularities seen of +/ K Represent density variations in the early universe formation of first galaxies and galaxy clusters The Big Bang The only viable cosmological theory is the Big Bang. The universe began as a great infusion of pure energy This energy, and space too, expanded and cooled into matter. This is a good theory because We see the expansion. We see a faint glow left from the original fireball! It correctly predicts chemical abundances of gas clouds. 5

6 Physics Fashion Once you can accept the universe as something expanding into an infinite nothing which is something, wearing stripes with plaid is easy. - Albert Einstein Measuring Cosmological Distances Cosmological Redshift and Hubble Law Brightness-Distance using Type 1a Supernova Type 1a supernova supernova of a white dwarf that is part of a binary star system. It is believed that these supernovae always reach the same maximum brightness. Measures distances to more than a billion light years. 6

7 Why Physical Science? Hymn #86, How Great Thou Art O Lord my God, when I in awesome wonder Consider all the worlds thy hands have made, I see the stars, I hear the rolling thunder, Thy pow r thru-out the universe displayed; Then sings my soul, my Savior God, to thee, How great thou art! How great thou art! 7