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Dark Matter & Dark Energy Northeastern Illinois University Dark Matter & Dark Energy Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Winter-Spring 2020 c 2012-2020 G. Anderson Introduction to Astronomy – slide 1 / 90 Northeastern Illinois Outline University Overview Dark Matter What is Dark Matter? Structure Hubble’s Law Our Accelerating Universe Review c 2012-2020 G. Anderson Introduction to Astronomy – slide 2 / 90 Northeastern Illinois University Overview A Great Unknown Pie Chart Visible Matter in the Universe Coma Cluster Dark Matter What is Dark Matter? Structure Overview Hubble’s Law Our Accelerating Universe Review c 2012-2020 G. Anderson Introduction to Astronomy – slide 3 / 90 Northeastern Illinois A Great Unknown University Q What is the universe made of? A Mostly, we do not know! The vast majority of the universe can not be “seen”, it is composed of dark matter and dark energy. c 2012-2020 G. Anderson Introduction to Astronomy – slide 4 / 90 Northeastern Illinois What is the Universe made of? University Dark Matter 24% Ordinary Matter 4.6%: ∼ Outside Stars: 3.8% Stars: 0.6% Dark Energy 71.4% ∼ The mass of dark matter in galaxies, clusters of galaxies, and the universe is five to six times the mass of ordinary matter. c 2012-2020 G. Anderson Introduction to Astronomy – slide 5 / 90 Northeastern Illinois Visible Matter in the Universe University Visible matter: stars, gas, dust There is more mass in gas than in stars. On large scales, > 100 1000 Mpc, matter appears∼ − to be isotropic and homogeneous. c 2012-2020 G. Anderson Introduction to Astronomy – slide 6 / 90 Northeastern Illinois The Coma Cluster University Large cluster, over 1000 galaxies, 99 Mpc from Earth. Visible Light X-ray Image M (6 to 7)M gas ≈ stars c 2012-2020 G. Anderson Introduction to Astronomy – slide 7 / 90 Northeastern Illinois University Overview Dark Matter Dark Matter & Dark Energy Q: “Dark” Matter? Early Dark Matter Discoveries Citations Zwicky (1933) Evidence for Dark Matter Dark Matter Merry-Go-Round Planet Speeds Rotation Curves Milky Way Dark Matter Halo Andromeda Rubin 16.07 The Andromeda Galaxy (M31) Expectations vs. Observations Q: Rotation Curves? Other Spirals Q: Rotation without DM? Milky Way Q: c Dark2012-2020 Matter G. Anderson Introduction to Astronomy – slide 8 / 90 Distribution? Northeastern Illinois Dark Matter & Dark Energy University We know very little about 95% of the universe which is dark invisible. Dark matter is the invisible mass which surrounds galaxies and galactic clusters. The presence of dark matter is inferred by its gravitational effects on observable stars, gas, galaxies, .... Dark energy is the energy which is causing the expansion of the universe to accelerate. dark energy = cosmological constant = vacuum energy c 2012-2020 G. Anderson Introduction to Astronomy – slide 9 / 90 Northeastern Illinois Q: “Dark” Matter? University Why do we call dark matter ”dark”? A) It absorbes light B) It is dark in color. C) It emits little or no radiation of any wavelength. D) It blocks out the light of stars in a galaxy. c 2012-2020 G. Anderson Introduction to Astronomy – slide 10 / 90 Northeastern Illinois Q: “Dark” Matter? University Why do we call dark matter ”dark”? A) It absorbes light B) It is dark in color. C) It emits little or no radiation of any wavelength. D) It blocks out the light of stars in a galaxy. c 2012-2020 G. Anderson Introduction to Astronomy – slide 10 / 90 Northeastern Illinois Early Dark Matter Discoveries University 1933 Zwicky measures radial velocities of eight galaxies in the Coma cluster and concludes M M . dark ≫ luminous 1935 Smith confirms Zwickly’s results for the Virgo cluster 1939 Babcock (M31) & 1940 Oort (NGC 3115) find unexpectedly large amounts of “dark” matter in spiral galaxies. 1959 Kahn & Wolter concluded that most of the mass of the Local Group exists in some invisible form. 1970 Rubin and Ford measure rotation curve of M31 and find evidence for dark matter. 1975 Roberts & Whitehurst observed the 21 cm line in M31 extending the flat rotation curve to 30 kpc. c 2012-2020 G. Anderson Introduction to Astronomy – slide 11 / 90 Northeastern Illinois Citations Zwicky (1933) University Year No. Citations 1955-59 2 1960-64 6 1965-69 5 1970-74 2 1975-89 63 1990-99 71 c 2012-2020 G. Anderson Introduction to Astronomy – slide 12 / 90 Northeastern Illinois Evidence for Dark Matter University From individual galaxies • – Rotation curves of spiral galaxies – Broadening of spectral lines in elliptical galaxies Clusters of galaxies • – Velocities of galaxies – Temperature of hot gas – Gravitational lensing Structure formation • Temperature fluctuations in the CMB • Primordial nucleosynthesis • c 2012-2020 G. Anderson Introduction to Astronomy – slide 13 / 90 Northeastern Illinois Merry-Go-Round University Rotation Curve A plot of orbital speed versus orbital distance from the center of rotation. v Cbc bc bc bc B A B C bc speed Abc distance r v = ω r × c 2012-2020 G. Anderson Introduction to Astronomy – slide 14 / 90 Northeastern Illinois Orbital Speeds of Planets University 12 vp =2πr v =2π r =2π r ⇒ p r3/2 10 bc Mercury 8 bc Venus bc 2π GM 6 v = = ⊙ bc √r q r Mars (AU/years) v 4 Jupiterbc Saturn bc Uranus 2 bc Neptunebc 0 0 10r (AU) 20 30 c 2012-2020 G. Anderson Introduction to Astronomy – slide 15 / 90 Northeastern Illinois Rotation Curves University M(r) = mass inside radius r. b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b GM(r) b b b b b b b b b b b b b vb (r)= b b b b b b r b q b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b bb b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b r b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b uniformb b densityb b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b decreasingb density b b b b b b b 2 b b b b b b b rv b b b b b b b b b b M(r)= b G b b b b b b b b c 2012-2020 G.
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