Dark Matter Carolyn Slivinski (Stsci)

Science Briefing October 5, 2017 What Lurks in the Dark? Dr. Simona Murgia (UC, Irvine) Dr. Will Dawson (Lawrence Livermore National Laboratory) An Exploration of Dark Matter Carolyn Slivinski (STScI) Facilitator: Dr. Emma Marcucci (STScI) Additional Resources http://nasawavelength.org/list/1929 Dark Matter Day: Primary Website Featured Activities: Jelly Bean Universe Find the Missing Mass – paper plate activity “Gravitational lensing” with a wine glass Basic Dark Matter Facts: Chandra Field Guide Ask an Astrophysicist Blog (archived) NASA’s Frontier Fields Additional Activities: Dark Matter Possibilities What’s the Matter? 2 Searching for Dark Matter with Gamma Rays Simona Murgia University of California, Irvine 3 Evidence for Dark Matter: A Brief Overview Evidence for dark matter is found at very different scales ‣ Galaxies ‣ Clusters of galaxies ‣ Universe 4 Galaxy Clusters The existence of dark matter was postulated by Fritz Zwicky in the 1930’s to explain the dynamics of galaxies in the Coma galaxy cluster Zwicky inferred the total mass of the cluster by measuring the velocities of its galaxies, based on Newtonian gravity. But the luminous mass (the galaxies in the cluster) was far smaller! F. Zwicky, Astrophysical Journal, vol. 86, p.217 (1937) Dark matter makes up for the missing mass Cluster DM Virial theorem: relates the velocity (dispersion, σ) of galaxies at some distance r from the cluster center to the enclosed mass Mtot(r) Velocities ~ 1000 km/s R ~ Mpcs Galaxy cluster: Distance ~100 Mpc ~1-2% stars, ~5-15% gas; the rest is dark matter (1 pc = 3.26 light yrs) 5 Rotation Curves of Galaxies Departures from the predictions of Newtonian gravity became apparent also at galactic scales with the measurement of rotation curves of galaxies (Rubin et al, 1970) However observed velocities stay Andromeda galaxy approximately constant, i.e. stars and gas move faster then predicted! Based on Newtonian dynamics, the velocity (v) of stars and gas in the galaxy should speed Rotational decrease with the distance (r) from the Distance from center center of the galaxy. and therefore: i.e. decreasing with r 6 Rotation Curves of Galaxies To reconcile theory with observations, postulate the existence of mass density not steeply falling as luminous matter density! By adding this extended matter halo, we find good agreement with observations Assume additional mass: therefore: and finally: Dark matter makes up e.g. Andromeda galaxy ➡ ~10 times more 11 Stars+gas: 1.4 ×10 M⊙ dark matter than for the missing mass 12 Total mass: 1.3×10 M⊙ luminous matter Corbelli et al (2009) Andromeda galaxy Dark matter Stellar disk Stellar bulge Gas 7 Cosmic Microwave Background Relic of a time in the early Universe when matter and radiation decoupled (protons and electron form neutral hydrogen and become transparent to photons, ~100,000s years after Big Bang) Universe was isotropic and homogeneous at large scales Very small temperature fluctuations, too small to evolve into structure observed today Require additional matter to T = 2.725 K start forming structure earlier ΔT ~ 200 μK Power spectrum of matter fluctuations Planck 2015 Observed (SDSS) baryons only Clumpiness et al et 2006 8 larger scales smaller scales Dodelson Dark Matter What data tell us about dark matter: ‣ makes up almost all of the matter in the Universe (present day Universe mostly made out of dark energy, dark matter, and small contribution from ordinary matter) ‣ interacts very weakly, and at least gravitationally, with ordinary matter ‣ is cold, i.e. non-relativistic 68% ‣ is neutral ‣ is stable (or it is very long-lived) 5% DARK ENERGY ➡But not what it is... DARK MATTER ORDINARY MATTER 27% 9 Dark Matter Candidates None of the known elementary particles has the right properties to be the dark matter Need new particles and new theories beyond the Standard Model of particle physics! Image credit: G. Bertone 10 Dark Matter Searches INDIRECT SEARCHES COLLIDER SEARCHES DIRECT SEARCHES Find its annihilation Detect energy it deposits byproducts Produce it in the lab Fermi-LAT CDMS Large Hadron Collider PAMELA 11 IceCube Indirect Dark Matter Searches Very rich search strategy, multi-messenger and multi-wavelength Gamma rays are particularly good probes to learn about the particle nature of dark matter via its annihilations DARK MATTER DISTRIBUTION ANNIHILATION PROCESS Simulated Milky Way-like dark matter halo: very dense at its center, large number of substructures + Via Lactea II (Diemand et al. 2008) 1 2 12 Gamma rays from Dark Matter Annihilation Dark matter substructures Galactic center Pieri et al, arXiv:0908.0195 13 Indirect Detection Results - Gamma Ray If a signal is detected, we can learn about the mass of the dark matter particle, how often it annihilates, how it is distributed in space, and constrain underlying theories Detection! Annihilation cross section section cross Annihilation how often annihilations occur) annihilations often how ( Dark matter particle mass 14 Indirect Detection Results - Gamma Ray If a signal is not detected, we can rule out many possibilities Ruled out Allowed Annihilation cross section section cross Annihilation how often annihilations occur) annihilations often how ( Dark matter particle mass 15 Fermi Mission The Large Area Telescope The Fermi Large Area Telescope (LAT) observes the gamma-ray sky in the 20 MeV to >300 GeV energy range with unprecedented sensitivity Orbit: 565 km, 25.6o inclination, circular. The LAT observes the entire sky every ~3 hrs (2 orbits) Fermi LAT Fermi LAT is a pair conversion telescope: gamma ray converts to electron-positron pairs which are recorded by the instrument 16 The Fermi LAT Gamma-Ray Sky Fermi LAT data 4 years, E > 1 GeV A potential dark matter signal must be disentangled from other more conventional (and brighter!) processes that produce gamma rays 17 A Dark Matter Signal from the Galactic Center? An excess in the Fermi LAT GC data consistent with dark matter annihilation was first claimed in 2009 (Goodenough and Hooper, arXiv:0910.2998.) More recent analyses are consistent with these results Properties of the dark matter particle and underlying particle physics model can be inferred However, other more mundane gamma-ray sources such as pulsars could explain the excess Image credit: NASA/T. Linden, U. Chicago C. Karwin et al, arXiv:1612.05687 Annihilation cross section cross Annihilation Dark matter particle mass 18 Caveats The determination of the Galactic center excess heavily relies on modeling of the gamma- ray emission from other processes (the excess is a small fraction of the total emission observed toward the Galactic center!) ➡Modeling of the gamma-ray sky is complex, and improvements are crucial to confirm the properties of the excess and to conclusively determine whether it originates from dark matter or something else! = + + data sources galactic interstellar isotropic emission + 19 dark matter?? Dark Matter Substructures Optically observed dwarf spheroidal galaxies: largest dark matter substructures predicted by simulations Excellent targets for gamma-ray dark matter searches ‣ Very rich in dark matter ‣ Expected to be free from other gamma ray sources, and therefore a potential signal is more easily interpreted compared to the Galactic center 20 Dwarf Spheroidal Galaxies Search for a signal in 25 dwarf spheroidal galaxies. No significant emission is found The limits probe a dark matter explanation of the Galactic center excess Fermi LAT Collaboration, arXiv 1503.02641 Ruled out Allowed Annihilation cross section cross Annihilation 21 Dark matter particle mass Dwarf Spheroidal Galaxies Search for a signal in 25 dwarf spheroidal galaxies. No significant emission is found The limits probe a dark matter explanation of the Galactic center excess Fermi LAT Collaboration, arXiv 1503.02641 Dark matter interpretation of Galactic center excess Annihilation cross section Annihilation cross 22 Dark matter particle mass Summary/Outlook Evidence for dark matter is overwhelming Many experiments have been relentlessly searching for dark matter particle candidates Gamma rays have been able to test and rule out many possibilities An intriguing excess originating from the Galactic center has been found; however, more work and improved understanding of the gamma-ray sky are necessary to determine its nature, dark matter or otherwise Thank you! 23 Will Dawson Lawrence Livermore National Lab LLNL-PRES-739383 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC Galaxy Cluster Mass ~ 1015 Solar Masses Abell 1689 25 NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM) Most people are familiar with 26 Credit: NASA CXC Astronomer’s Periodic Table 27 Credit: NASA CXC A new component to clusters 28 Accelerating electrons emit photons 29 Chandra X-ray Map of the Cluster Plasma Abell 1689 30 X-ray: NASA/CXC/MIT/E.-H Peng et al; Optical: NASA/STScI Far more of the mass is in the X-ray emitting intracluster plasma 31 Cosmologist’s Periodic Table Dark Matter 32 Gravitational lensing best tool for studying dark matter 33 Zwicky (1937) Mass warps space-time and alters the path of light 34 Gravitational lensing distorts galaxy images 35 36 37 38 39 Gravitational lensing of clusters not observed until 1990 Tony Tyson 40 Weighing clusters with weak gravitational lensing Abell 1689 41 Tyson et al. (1990) The first gravitational lensing mass map Abell 1689 42 Tyson et al. (1990) Thanks to Hubble a lot has improved in past 20 years Abell 1689 43 NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM) Much higher resolution mass maps Abell 1689 44 NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM) For some clusters the X-ray plasma and dark matter distributed similarly X-ray Plasma Dark Matter Abell 1689 Abell 1689 X-ray: NASA/CXC/MIT/E.-H Peng et al; Optical: NASA/STScI NASA, ESA, E.

Load more