Slide 1Slide 2Normal and Active GalaxiesActive Galactic Nuclei (AGN)‏Evolution of Galaxies:AGN Energy SourceCosmic Distance ScaleSlide 8Cosmological Structure?No Structure on Largest Scales (Galaxies distributed fairly uniformly)‏Slide 11Slide 12Hubble Expansion AnalogyThe Fate of the UniverseSlide 15QuestionThe Big BangSlide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24The Drake EquationSlide 26Slide 27Slide 28Types of Galaxies Elliptical: Spiral:Irregular:Milky Way GalaxySupermassive Black Hole at center~ 1 Million Solar MassesSun - 2/3 of the way out on a spiral armNormal and Active GalaxiesHow do the luminosities of normal and active galaxies compare?What about their spectra?What resides at the center of most galaxies, including our own? Where is the Sun?Active Galactic Nuclei (AGN) Several hundreds of trillions of solar luminosities! Spectrum is not black body => luminosity not due to starlight alone! What is the power source?Evolution of Galaxies:Caused by merging and interactions betwe en Galaxies.AGN Energy SourceRapidly varying intensity => small sizeHigh luminosity and small size => supermassive black hole Billions of solar masses!Consumes entire stars!Cosmic Distance Scale “Standard Candles”Extremely bright events with well-known luminositiesEx. Type Ia (carbon-detonation) supernovaeWorks out to ~ 3 billion light years!Recall: Apparent Brightness = Luminosity/Distance^2Structures of GalaxiesOn intermediate scales, galaxies form identifiable structures. Groups Clusters SuperclustersThe “Local” SuperclusterCosmological Structure?How is matter distributed in the universe on the very largest scales?No Structure on Largest Scales (Galaxies distributed fairly uniformly) Surprising given observations of groups, clusters, and superclusters on smaller scalesCosmological Principle:Universe is homogeneous and isotropicHomogeneity => ?Isotropy => ?Olbers` ParadoxIf universe is homogeneous, isotropic, infinite in extent, and unchanging, then any line of sight from Earth shouldeventually run into a star.What observable effect would this have on the night sky?Why isn't this what we see?The universe is expanding=> Assumption that universe is unchanging is incorrect => Doesn’t matter whether universe is finite or infinite, we only see a finite part=> Light from objects greater than 14 billion light years away has not had time to reach us!Hubble Expansion Analogy1 Mpc 6 Mpc 12 Mpc2 Mpc 12 Mpc 24 Mpc Accuracy increases with distance. The farther out , the faster the expansion. Works for any chosen point of reference. Hubble's Law: v = H0 x distance1 pc ~ 3 Light YearsThe Fate of the UniverseWhat property determines the ultimate fate of the universe?What does the best available data tell us about how the expansion rate of the universe is changing?Affect of Density on the UniverseAs best we can tell, the expansion rate of the universe is increasing!QuestionWhat is it that is causing the expansion of the universe to accelerate?What is the biggest single contributor to the overall density of the universe?DARK ENERGYThe Big Bang Primordial explosion thought to be the creation of our universe – all matter and space, “beginning” of time. Hot and dense conditions => early universe was opaque to radiation! Primordial nucleosynthesis Source of Cosmic Microwave Background RadiationPrimordial Nucleosynthesis Creation of base level of helium (~25%) in the early universe Stopped because temperature and density became too low (due to expansion) for fusion to continueAlso, Hubble's Law and CMBREvidence for the Big BangThe Horizon ProblemCMBR - Leftover radiation from the Big BangHow is the CMBR distributed across the sky?Why is this a problem?The Flatness ProblemThe cosmic density appears to be fairly close to the critical valueNo obvious reason why universe should have exactly the critical density! What theory solves both the horizon and flatness problems?The Theory of InflationThe universe swelled in size by a factor of about 1050 in only 10-32 seconds!Solves both horizon and flatness problems! How?Extraterrestrial Life (as We Know It)“Life as we know it” is generally taken to mean carbon-based life that originated in a liquid-water environment. Requirements?Liquid water, protection from radiation, temperate climateWhat are some important characteristics of living organisms?Characteristics of a Living OrganismResponsiveness to environmentReproduction/replicationCapacity to evolveAbility to take in nourishment, grow, and healThe Miller-Urey experiment attempts to recreate the chemical conditions of the primitive Earth in the laboratory, and synthesize some of the building blocks of life.Supports the assumptions of mediocrity!The Drake EquationWhat is the Drake equation designed to estimate?Which terms have astronomers measured most accurately?The Drake Equationnumber of technological, intelligent civilizations in the Milky Wayrate at which new stars are formed (avg. over galactic lifetime)=xfraction of stars having planetary systemsxaverage number of habitable planets within those planetary systemsxfraction of those habitable planets on which life arisesxfraction of those life-bearing planets on which intelligence evolvesfraction of those planets with intelligent life that develop technological societyaverage lifetime of a technological civilizationxxEach term is less certain than the preceding one! Only in last ten years have we addressed the second term.SETI Search for ExtraTerrestrial Intelligence- Listens for radio signals from alien worlds Microwave Window - in radio part of EM spectrum - Minimal noise - Referred to as the “Water Hole”Good luck and have a great