Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW1Questions of the Day•What does the large scale structure of the Universe look like?•Why would the expansion of the Universe lead everyone, everywhere to measure the Hubble Diagram?•Why do some things in the Universe NOT expand along with it?•What is the origin of the cosmological redshift, and how is it different than the Doppler redshift?•Why does the expansion of the Universe suggest that the Universe had a beginning?Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW2How to build a better redshift map:To go farther: Need spectra of fainter galaxiesTo cover more area: Need more spectraAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW3There are special spectrographs that can measure hundreds of redshifts at the same time!Each red cable contains an optical fiber, which goes into a spectrograph.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW4Each fiber gets placed on top of a different galaxy.Measure spectra of 100’s of galaxies at the same time. Gobs of redshifts, quickly!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW5400 simultaneous spectra!Each row is one spectrum of one galaxyAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW6Spatial distribution of nearby galaxiesColor indicates redshift: blue = close red = further (0.04<z<0.1)2MASSAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW7Shells of the Nearby UniverseAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW8>100,000 of galaxies!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW9The Sloan Digital Sky Survey (SDSS): nearly 1 million galaxies!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWA Movie of the Sloan Survey:10Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW11At large scales, the Universe does start to look more homogeneous…Distribution & size of voids becomes uniformAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW12Why is the distribution so lumpy on smaller (10 Mpc) scales?Why are there galaxies here?… but not here?Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW13The Universe starts out as mostly smooth……but it has tiny little ripples in it.“Density Fluctuations”Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW14Gravity turns these little ripples into big ones!N-body Simulations of “Large Scale Structure”Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW15Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW16Large Scale Structure is another test of how dark matter behaves“Cold” Dark MatterHeavy dark matter particles lumber along slowly. Easy for gravity to collect them in small lumps.“Warm” Dark MatterLighter dark matter particles move faster“Hot” Dark MatterLow mass dark matter particles move at close to the speed of light!Washes out “small scale” structureAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXMost galaxies are in “filaments”.Clusters are at the intersection of filaments!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW17Why in the world is this true???•Why is just about every single galaxy in the world moving away from us??? ! v = H0dAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXAre we at the center of a big explosion???• No! The Whole Universe is Expanding!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW18The Hubble Law implies that the entire Universe is expanding! ! v = H0dThe Hubble Law says that distant galaxies are receding from us!They’re getting further awayOccurs in every direction!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW19But, unless we’re in a very special place, residents of all galaxies must see the same thing! ! v = H0dThe (insert name of alien astronomer here) Law says that distant galaxies are receding from us!They’re getting further awayInsert initial of alien astronomerAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXThe only possible interpretation is that every galaxy is becoming more distant from every other galaxy!• We see all galaxies rushing away from us.• Residents of Planet Xork in Galaxy Grignik see all galaxies rushing away from them.• Residents of Planet YubYub…etc.The whole Universe is expanding!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW20Why does further=faster imply expansion?Easier to show that expansion implies further=fasterExpands x2!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW21It doesn’t matter where you are!•If everything’s expanding, everyone sees the Hubble Law.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW22Expansion Explains Why…•Further = Faster•We’re not so special!•Instead, everybody’s special.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW23A map of the Local Universe…You are hereAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXA map of the Expanded Local Universe…Slide this over the previous map!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXOverlaying maps, shows apparent Hubble LawYou are hereAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXBut, with a different alignment, expansion seems to “centered” elsewhere…Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWX… or “centered” somewhere else.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW24Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW25What the heck is an expanding universe?•On large scales, every point in space is getting further away from every other point in space.P.S. The “on large scales” bit is critical!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW26Remember that curved space stuff????•Space is malleable!•It curves & stretches!(…like the surface of a balloon..)Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW27Every galaxy is becoming more distant from every other galaxy!• Every point on the surface of an inflating balloon is becoming further away from every other point!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW28The surface of an expanding sphere (balloon) is a reasonable 2-D analog of what our 3-D space is doing…•There’s no
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