Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Timeline of astronomy wikipedia , lookup
Wilkinson Microwave Anisotropy Probe wikipedia , lookup
Anthropic principle wikipedia , lookup
Dark energy wikipedia , lookup
Expansion of the universe wikipedia , lookup
Shape of the universe wikipedia , lookup
Non-standard cosmology wikipedia , lookup
Observable universe wikipedia , lookup
Lambda-CDM model wikipedia , lookup
A100H–Exploring the Universe: Dark Matter, Dark Energy Martin D. Weinberg UMass Astronomy [email protected] April 21, 2016 Read: Chap 23 04/21/16 – slide 1 Announcements ⊲ Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time Read: Chap 23 Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here! ⊲ ⊲ ⊲ Emphasizes Chapters 19–23 Some topics from entire course folded in . . . Same format: approximately 2/3 multiple choice, 1/3 short answer 04/21/16 – slide 2 Announcements ⊲ Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time Read: Chap 23 Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here! Today: Dark Matter & Dark Energy and the Big Bang ⊲ ⊲ What is the evidence for dark matter and dark energy? What does this imply about the future of the Universe? 04/21/16 – slide 2 Announcements ⊲ Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time Final Exam: Friday 29 Apr at 10:30 am–12:30 pm, here! Today: Dark Matter & Dark Energy and the Big Bang ⊲ ⊲ What is the evidence for dark matter and dark energy? What does this imply about the future of the Universe? Your questions? Read: Chap 23 04/21/16 – slide 2 What is dark matter? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Two Basic Options for Dark Matter 1. Ordinary Dark Matter (MACHOS) Massive Compact Halo Objects: dead or failed stars in halos of galaxies 2. Extraordinary Dark Matter (WIMPS) Weakly Interacting Massive Particles: neutrino-like particles Read: Chap 23 mysterious 04/21/16 – slide 3 What is dark matter? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Two Basic Options for Dark Matter 1. Ordinary Dark Matter (MACHOS) Massive Compact Halo Objects: dead or failed stars in halos of galaxies 2. Extraordinary Dark Matter (WIMPS) Weakly Interacting Massive Particles: neutrino-like particles mysterious Best bet! Read: Chap 23 04/21/16 – slide 3 Why believe in WIMPS? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Read: Chap 23 1. There is not enough ordinary matter 2. WIMPs could be left over from Big Bang 3. Models involving WIMPs explain how galaxy formation works 04/21/16 – slide 4 Why believe in WIMPS? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ 1. There is not enough ordinary matter 2. WIMPs could be left over from Big Bang 3. Models involving WIMPs explain how galaxy formation works Projected view of n-body simulation Read: Chap 23 04/21/16 – slide 4 Why believe in WIMPS? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ 1. There is not enough ordinary matter 2. WIMPs could be left over from Big Bang 3. Models involving WIMPs explain how galaxy formation works Projected view of n-body simulation Read: Chap 23 04/21/16 – slide 4 Why believe in WIMPS? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ 1. There is not enough ordinary matter 2. WIMPs could be left over from Big Bang 3. Models involving WIMPs explain how galaxy formation works “Pie diagrams” Read: Chap 23 04/21/16 – slide 4 Why believe in WIMPS? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time LSS data and simulations compared ⊲ Read: Chap 23 04/21/16 – slide 5 Why believe in WIMPS? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time LSS data and simulations compared ⊲ Read: Chap 23 04/21/16 – slide 5 Why believe in WIMPS? Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time LSS data and simulations compared ⊲ Read: Chap 23 04/21/16 – slide 5 Summary I Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time What is the evidence for dark matter in galaxies? ⊲ ⊲ Rotation curves of galaxies are flat, indicating that most of their matter lies outside their visible regions What is the evidence for dark matter in clusters of galaxies? ⊲ Masses measured from galaxy motions, temperature of hot gas, and gravitational lensing all indicate that the vast majority of matter in clusters is dark What is the evidence for dark matter on very large scales? ⊲ Read: Chap 23 The distribution of galaxies and clusters in the Universe are consistent with simulations only when dark matter is included 04/21/16 – slide 6 Dark-Matter Detection Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time If dark matter is made up of WIMPs, then millions, possibly billions, of WIMPs must pass through every square centimeter of the Earth each second! ⊲ Read: Chap 23 04/21/16 – slide 7 Dark-Matter Detection Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time If dark matter is made up of WIMPs, then millions, possibly billions, of WIMPs must pass through every square centimeter of the Earth each second! ⊲ Two types of experiments designed to look for WIMPS 1. Direct detection experiments Look for the scattering of dark matter particles off atomic nuclei within a detector The Axion Dark Matter eXperiment (ADMX) searches for axions 2. Indirect detection Look for the products of WIMP annihilation Read: Chap 23 04/21/16 – slide 7 Direct detection Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Direct detection experiments operate deep underground to reduce the interference from cosmic rays. Typically use either cryogenic or noble liquid detector technologies. ⊲ ⊲ Read: Chap 23 Cryogenic detectors operating at temperatures below 100mK, detect the heat produced when a particle hits an atom in a crystal absorber such as germanium. Noble liquid detectors detect scintillation produced by a particle collision in liquid xenon or argon. 04/21/16 – slide 8 Direct detection Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Read: Chap 23 SLAC argon detector 04/21/16 – slide 9 Direct detection Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Two of the Italian DAMA (for DArk MAtter) collaboration experiments detected an annual modulation in the event rate that they claim is due to dark matter. As the Earth orbits the Sun, the velocity of the detector relative to the dark matter halo will vary by a small amount. This claim is so far unconfirmed and unreconciled with negative results of other experiments. Read: Chap 23 04/21/16 – slide 10 Indirect detection Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ If WIMPs are their own antiparticle, two WIMPs could annihilate to produce: ⊲ ⊲ gamma rays particle-antiparticle pairs If the WIMP is unstable, WIMPs could decay into particles These processes could be detected indirectly through ⊲ ⊲ an excess of gamma rays anti-protons or positrons emanating from high density regions Fermi Gamma-ray Space Telescope is currently being used to look for indirect signals Read: Chap 23 04/21/16 – slide 11 Indirect detection Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ WIMPs passing through the Sun or Earth may scatter off atoms and lose energy! ⊲ ⊲ ⊲ ⊲ Read: Chap 23 WIMPs may accumulate at the center of these bodies, increasing the chance of collision/annihilation Could observe distinctive signal in the form of high-energy neutrinos Such a signal would be strong indirect proof of WIMP dark matter Neutrino telescopes are searching for this signal 04/21/16 – slide 12 Summary I Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time Does dark matter really exist? ⊲ ⊲ Read: Chap 23 Either dark matter exists or our understanding of our gravity must be revised What might dark matter be made of? ⊲ There does not seem to be enough normal (baryonic) matter to account for all the dark matter, so most astronomers suspect that dark matter is made of (non-baryonic) particles that have not yet been discovered 04/21/16 – slide 13 The Fate of the Universe Will the Universe continue expanding forever? Does the Universe have enough kinetic energy to escape its own gravitational pull? ⊲ ⊲ ⊲ Application of General Relativity to the entire Universe Solve for motion in 4-dimensional space-time Trade off between energy of expansion and self-gravity of all the mass and energy! Read: Chap 23 04/21/16 – slide 14 The Fate of the Universe Will the Universe continue expanding forever? Does the Universe have enough kinetic energy to escape its own gravitational pull? ⊲ ⊲ ⊲ ⊲ Application of General Relativity to the entire Universe Solve for motion in 4-dimensional space-time Trade off between energy of expansion and self-gravity of all the mass and energy! Einstein’s equations Rµν 1 8πG − R gµν + Λ gµν = 4 Tµν , 2 c Cosmological constant Read: Chap 23 04/21/16 – slide 14 The Fate of the Universe Will the Universe continue expanding forever? Does the Universe have enough kinetic energy to escape its own gravitational pull? Fate of Universe depends on the amount of dark matter 2-d sketch of possible solutions Read: Chap 23 04/21/16 – slide 14 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Closed Universe: there is enough matter in the Universe that gravity will eventually overcome the expansion of space ⊲ ⊲ ⊲ ⊲ This geometry has positive curvature Parallel lines converge Matched Einstein’s original model without a cosmological constant What is the cosmological constant? ◦ ◦ Read: Chap 23 Value of the energy density of the vacuum Introduced to “hold back gravity” and achieve a static universe 04/21/16 – slide 15 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Closed Universe: there is enough matter in the Universe that gravity will eventually overcome the expansion of space Open Universe: there isn’t enough matter to stop expansion, so the Universe will continue to expand forever at the same rate ⊲ ⊲ Read: Chap 23 This space-time has negative curvature (saddle-shaped) Parallel lines diverge 04/21/16 – slide 15 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Closed Universe: there is enough matter in the Universe that gravity will eventually overcome the expansion of space Open Universe: there isn’t enough matter to stop expansion, so the Universe will continue to expand forever at the same rate Flat Universe: the expansion of the Universe and the density of matter perfectly balance out, so the Universe’s expansion slows down over time but never quite stops completely ⊲ ⊲ Read: Chap 23 This space has no overall curvature Parallel lines stay parallel 04/21/16 – slide 15 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Read: Chap 23 04/21/16 – slide 16 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Read: Chap 23 Fate of Universe depends on the amount of dark matter 04/21/16 – slide 17 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Read: Chap 23 Amount of dark matter is ≈ 25% of the critical density suggesting fate is eternal expansion 04/21/16 – slide 18 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Estimated age depends on both dark matter and dark energy Read: Chap 23 04/21/16 – slide 19 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time But expansion appears to be speeding up! ⊲ Dark energy?? Read: Chap 23 04/21/16 – slide 20 The Fate of the Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time But expansion appears to be speeding up! ⊲ Dark energy?? [We invoke the existence of some unknown physics . . . ] Read: Chap 23 04/21/16 – slide 20 Accelerating Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Accelerating Universe is best fit to supernova data Read: Chap 23 04/21/16 – slide 21 Accelerating Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Accelerating Universe is best fit to supernova data Read: Chap 23 04/21/16 – slide 21 Accelerating Universe Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time Nobel Prize 2011 ⊲ Read: Chap 23 04/21/16 – slide 22 Summary II Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time Will the Universe continue expanding forever? ⊲ Is the expansion of the Universe accelerating? ⊲ Read: Chap 23 Current measurements indicate that there is not enough dark matter to prevent the Universe from expanding forever ⊲ An accelerating Universe is the best explanation for the distances we measure when using white dwarf supernovae as standard candles 04/21/16 – slide 23 Summary II Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time Will the Universe continue expanding forever? ⊲ Is the expansion of the Universe accelerating? ⊲ ⊲ ⊲ Read: Chap 23 Current measurements indicate that there is not enough dark matter to prevent the Universe from expanding forever An accelerating Universe is the best explanation for the distances we measure when using white dwarf supernovae as standard candles This implies that one could travel forever in a chosen direction! 04/21/16 – slide 23 Extrapolate the expansion back in time Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting . . . What happens? ⊲ Read: Chap 23 04/21/16 – slide 24 Extrapolate the expansion back in time Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting . . . What happens? The density increases. The temperature increases. ⊲ Read: Chap 23 04/21/16 – slide 24 Extrapolate the expansion back in time Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ Read: Chap 23 The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting . . . What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star 04/21/16 – slide 24 Extrapolate the expansion back in time Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting . . . What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Read: Chap 23 04/21/16 – slide 24 Extrapolate the expansion back in time Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting . . . What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Still later, the temperatures get so high that the baryons break up into constituent sub-particles (quarks). Read: Chap 23 04/21/16 – slide 24 Extrapolate the expansion back in time Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting . . . What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Still later, the temperatures get so high that the baryons break up into constituent sub-particles (quarks). ???? Read: Chap 23 04/21/16 – slide 24 Extrapolate the expansion back in time Announcements What is DM? Why WIMPS? Summary I Dark-Matter Detection The Fate of the Universe Accelerating Universe Accelerating Universe Summary II Back in time ⊲ The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting . . . What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Still later, the temperatures get so high that the baryons break up into constituent sub-particles (quarks). ???? Realm of the Early Universe Read: Chap 23 04/21/16 – slide 24