Chapter 16 Dark Matter Dark Energy and the Fate of the Universe Copyright 2009 Pearson Education Inc Havasupai Indians Copyright 2009 Pearson Education Inc Do you believe the blood should be returned A Yes B No Copyright 2009 Pearson Education Inc 16 3 Structure Formation Our goals for learning What is the role of dark matter in galaxy formation What are the largest structures in the universe Copyright 2009 Pearson Education Inc What is the role of dark matter in galaxy formation Copyright 2009 Pearson Education Inc Gravity of dark matter is what caused protogalactic clouds to contract early in time Copyright 2009 Pearson Education Inc WIMPs can t contract to the center because they don t radiate away their orbital energy Copyright 2009 Pearson Education Inc Dark matter is still pulling things together After correcting for Hubble s law we can see that galaxies are flowing toward the densest regions of space Copyright 2009 Pearson Education Inc What are the largest structures in the universe Copyright 2009 Pearson Education Inc Maps of galaxy positions reveal extremely large structures superclusters and voids Copyright 2009 Pearson Education Inc Time in billions of years 0 5 2 2 5 9 8 6 13 7 13 35 70 93 140 Size of expanding box in millions of light years Models show that the gravity of dark matter pulls mass into denser regions the universe grows lumpier with time Copyright 2009 Pearson Education Inc Models show that gravity of dark matter pulls mass into denser regions the universe grows lumpier with time Large Scale Structure of the Universe Copyright 2009 Pearson Education Inc Structures in galaxy maps look very similar to the ones found in models in which dark matter is WIMPs Copyright 2009 Pearson Education Inc What have we learned What is the role of dark matter in galaxy formation The gravity of dark matter seems to be what draws gas together into protogalactic clouds initiating the process of galaxy formation What are the largest structures in the universe Galaxies appear to be distributed in gigantic chains and sheets that surround great voids Copyright 2009 Pearson Education Inc 16 4 The Fate of the Universe Our goals for learning Will the universe continue expanding forever Is the expansion of the universe accelerating Copyright 2009 Pearson Education Inc Will the universe continue expanding forever Copyright 2009 Pearson Education Inc Does the universe have enough kinetic energy to escape its own gravitational pull Fate of a Launched Cannonball Copyright 2009 Pearson Education Inc Fate of universe depends on the amount of dark matter Lots of dark matter Copyright 2009 Pearson Education Inc Critical density of matter Not enough dark matter Amount of matter is 25 of the critical density suggesting fate is eternal expansion Not enough dark matter Copyright 2009 Pearson Education Inc But expansion appears to be speeding up Dark energy Copyright 2009 Pearson Education Inc Not enough dark matter old older oldest Estimated age depends on both dark matter and dark energy Copyright 2009 Pearson Education Inc Thought Question Suppose that the universe has more dark matter than we think there is today How would that change the age we estimate from the expansion rate A Estimated age would be older B Estimated age would be the same C Estimated age would be younger Copyright 2009 Pearson Education Inc Thought Question Suppose that the universe has more dark matter than we think there is today How would that change the age we estimate from the expansion rate A Estimated age would be older B Estimated age would be the same C Estimated age would be younger Copyright 2009 Pearson Education Inc Is the expansion of the universe accelerating Copyright 2009 Pearson Education Inc The brightness of distant white dwarf supernovae tells us how much the universe has expanded since they exploded Copyright 2009 Pearson Education Inc An accelerating universe is the best fit to supernova data Copyright 2009 Pearson Education Inc What have we learned Will the universe continue expanding forever Current measurements indicate that there is not enough dark matter to prevent the universe from expanding forever Is the expansion of the universe accelerating An accelerating universe is the best explanation for the distances we measure when using white dwarf supernovae as standard candles Copyright 2009 Pearson Education Inc
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