Deep Extragalactic Space The basic yardstick of distance is now the Megaparsec = 3.3 million light years Question: how do we determine the distances to such remote objects? Examples of extremely distant clusters of galaxies You cant see Cepheids that far out The Hubble Relation for Galaxies Galaxies in all directions receding from us The more distant they are, the faster they are receding v=H 0 d v = speed of recession (km/sec), d= distance (Mpc), H 0 Hubble Constant, (km/sec/Mpc), H 0 = 70 km/sec/Mpc The Hubble Relation for Galaxies If you measure the redshift, you know the distance With measurements of distances, you can map out the distribution of galaxies What is the meaning of Hubbles Law? Are we at the center of the universe and everything is moving away from us? True analogy: observer on an expanding jungle gym The universe is expanding Hubble Law was the beginning of the science of cosmology First, lets examine some of the variety in the hundreds of thousands of galaxies that have been examined An interludeRadio Astronomywill make sense later To remind you of what you already know. Radio astronomy = study of universe with EM waves having wavelength from about 1 millimeter to 50 meters Comparison: optical astronomy studies wavelengths between 4E-07 to 7E-07 meters The Radio Sky Radio sources many associated with giant elliptical galaxies A region 2 degrees square at RA=23h, Dec=20d. The sky at 21cm wavelength Radio Galaxies, e.g. 3C296 Radio galaxies shine by a mechanism called synchrotron radiation What is synchrotron radiation? Accelerated electrons radiate EM waves DEMO History of Radio Astronomy, circa 1960 Some of the brightest radio sources, 3C48, 3C273, did not seem to be associated with galaxies, but with star-like objects Spectra of these sources showed highly redshifted lines great distances Z = (w-w 0 )/w 0 = 0.16, 0.48, 1.7, 4.42 !! Quasar = Quasi-Stellar Radio Sources With Hubble Space Telescope, we have imaged Quasars What are quasars? Artistic view of an early quasar Physically what They are In quasars and radio galaxies, there is a connection from the small to the extremely large: M87 M87 at radio wavelengths: it exists on many scales The Central Engines of quasars and radio galaxies: black holes of billion solar masses Summary of Quasar Characteristics Clearly are a brilliant, energetic phenomenon in centers of galaxies Quasars are very distant. We see them as they were long ago Lets look at the distribution of quasar redshifts Question: what does this mean? 7236 quasars Extragalactic Astronomy as a Time Machine