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Published byJulian Richard Modified over 9 years ago
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MAPping the Universe ►Introduction: the birth of a new cosmology ►The cosmic microwave background ►Measuring the CMB ►Results from WMAP ►The future of cosmology Susan Cartwright University of Sheffield
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The Birth of a New Cosmology ►Cosmology is the science of the whole universe its origin its structure and evolution ►Cosmological data must apply to the whole universe large distances faint sources large uncertainties “Cosmology in the 1950s was a science of 2½ facts.”Cosmology in the 1950s was a science of 2½ facts 1980s: maybe 8 facts, but all with factor ~2 uncertainty!
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Precision Cosmology ►Aim: determine cosmological parameters to a few percent H 0 : the expansion rate of the universe and how it changes over time k: its geometrygeometry Ω: its density Ω b : the density of ordinary matter Ω m : the density of all matter Ω Λ : the “dark energy” (or “cosmological constant”) t 0 : its age
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Steps towards precision abundances of light elements: measuring Ω b h 2 type Ia supernovae: measuring Ω Λ − Ω m
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More steps… ►HST Key Project on Extragalactic Distance Scale H 0 using variety of methods result: 72 ± 4 ± 7 km/s/Mpc 10% accuracy dominated by systematics need an independent technique: the Cosmic Microwave Background
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What is it? ►Look at the sky at wavelengths of a few mm (microwaves) very uniform faint glow spectrum is thermal, temperature ~3 K discovered accidentally by Penzias and Wilson in 1965 predicted years earlier by Gamow et al. as consequence of Big Bang
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Where did it come from? ►Early universe was hot, dense and ionised photons repeatedly interacted with protons and electrons: universe opaque result: thermal (blackbody) spectrum ►Universe expands and cools at ~3000 K neutral atoms form: universe transparent photons no longer interact with matter thermal spectrum cools as expansion continues
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What does it tell us? ►The Big Bang happened! no other way to generate a uniform thermal spectrum ►The universe was very uniform when it was emitted about 300000 years after the Big Bang ►So how did galaxies form then? well…it’s not exactly uniform
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Anisotropies ►Our rest frame ≠ CMB rest frame dipole anisotropy of ~0.1% ►Foreground sources most obviously our own Galaxy ►Density fluctuations in early universe anisotropies of ~10 -5 seeds of galaxy formation COBE data
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Generation of anisotropies ►Density fluctuations in early universe series of potential wells oscillations in and out of wells ►characteristic size = horizon radius present size of horizon radius depends on geometry of universe Pictures by Wayne Hu
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Measuring a map ►Need to quantify anisotropies express as sum of increasingly high-frequency components (similar to sythesiser) plot amplitudes of successive components
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CMB Power Spectrum
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Cosmological parameter dependence Movies from Martin White’s website Hubble parameter Cosmological constant Baryon density Spectral index
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Making a map COBE satellite: discovered the fluctuations BOOMERanG balloon: first of the new generation
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More Mappers the Cosmic Background Imager the Very Small Array
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WMAP the Wilkinson Microwave Anisotropy Probe orbiting the Sun/Earth L2 point better view, less background
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WMAP results ►Map covers whole sky resolution ~0.2° good power spectrum to 3 rd peak also measuring polarisation
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WMAP Cosmology ►h = 0.72 0.05 ►Ω b h 2 = 0.0226 0.0008 ►Ω m h 2 = 0.133 0.006 ►Ω tot h 2 = 1.02 0.02 ►Ω h 2 < 0.0076 (95%) ►n = 0.99 0.04 ►age of universe = 13.7 0.2 Gyr (WMAP only) (also uses 2dF and Ly α) first stars born 200 Myr after Big Bang
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Conclusion ►The Universe is dominated by dark energy why? how? what? ►About 85% of the matter in the universe is non- baryonic cold dark matter not atoms not neutrinos ►The Universe is about 14 billion years old, and will expand forever ►Cosmology is no longer a science of 2½ facts!
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