Expansion of the Universe Alexandra Higareda DeMaris Wilson

Introduction Albert Einstein's General Theory of Relativity "the greatest blunder of my life" Enter Hubble

Expansion of the Universe Hubble found straight-line relationship existed between redshifts interrupted as recessional velocities and galaxies distance Farther away is a galaxy, faster it is moving away from our Galaxy Only exceptions were several nearby galaxies that are blueshifted

Galaxy Redshifts 1928, large redshifts in absorption lines of all but 5 of 41 nearby galaxies were found 5 galaxies having blueshifted spectra Even larger redshifts have since been found for fainter galaxies

Hubble Velocity-Distance Law Greater recessional velocity, fainter a galaxy appears and more distant it is Hubble's velocity-distance law - farther away a galaxy is from our Galaxy, faster that galaxy is receding from us Recessional velocity equals constant times distance Equation: v = H r, where constant of proportionality H is called Hubble's constant Interpretation - redshifts of distant galaxies represents amount universe has expanded since galaxy's light was emitted Redshifts are result of expansion of universe not high velocities as in Doppler effect

Universal Scaling Factor Could be thought of as typical separation between galaxies or clusters of galaxies Has same value everywhere at any instant of time Equation: z = Dl / l = ( R o - R ) / R, where R o = present value of universal scaling factor, R = value at some earlier time Wavelengths are lengths and hence as space grow so do wavelengths

Cosmological Redshifts Not same as Doppler redshift Not same as gravitational redshift Galaxies also exhibit a small peculiar velocity superimposed on expansion velocity Peculiar velocity larger than recessional velocity for nearby galaxies Thus we observe blueshifted galaxies

Cosmological redshifts continued… Recessional velocity much larger than peculiar velocity for very distant galaxies Thus we may neglect peculiar velocity in comparison Measures of Hubble's constant lie between km/s/Mly or km/s/Mpc Example - largest redshifts for supposedly normal galaxies are about 1.2, recessional velocity of 200,000 km/s for Hubble constant equal 17 km/s/Mly

Hubble Constant Hubble time (1/H) - reciprocal of Hubble constant has units of time; represents time since initiation of expansion of space if expansion has proceeded uniformly Equation: distance = constant*velocity*time, or r = z c / H

Hubble Times Hubble"s Constant (km/s/Mly) Hubble Time (y) 1520 x x x x 10 9 Hubble Times

Look-Back Effect Galaxies whose distances are as much as 11 x 10 9 ly (11,000 Mly) are observed as they were 11 billion years ago, not as they are now Some quasars redshifts over 3 and a few over 4 with largest around 5 Distances equal almost 15 x 10 9 ly (15,000 Mly) These objects seen when they are but a few percent of current age of universe

Cosmic Distance Scale Proceeds from nearest objects to farthest 1st link - parallactic distances of relatively nearby stars from parallactic shifts 2nd link - inverse-square distances of variable stars, chiefly Cepheids, and distances from spectroscopic and intrinsic brightness of stars in our Galaxy 3rd link - inverse-square distances of neighboring galaxies of Local Group Determined from characteristics of brightest stars, Cepheid variables, and other stellar data

Comic Distance Scale continued… 4th link - inverse-square distances of "nearby galactic groups" taking as distance indicators their brightest stars, surface brightness of galaxies, and apparent size of bright gaseous nebulae 5th link - inverse-square distances of galaxies, such as Virgo cluster, using cluster's brightest galaxy or its luminosity type as standard of comparison 6th link - expansion distances of most remote clusters of galaxies by means of Hubble constant derived from expansion of universe

The End