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 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 Annihilationcross
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. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM) 45 Merging galaxy clusters are an exception
Bullet Cluster
46 X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al. Merger Scenario
S
N
Dark Dark Matter
Matter Gas + Gas Galaxies Key
47 Merger Scenario
S
Gravitational Attraction
N
Dark Dark Matter
Matter Gas + Gas Galaxies Key
48 Merger Scenario
S N
Dark Dark Matter
Matter Gas + Gas Galaxies Key
49 Merger Scenario
S N
Dark Dark Matter
Matter Gas + Gas Galaxies Key
50 Merger Scenario
N+S
Dark Dark Matter
Matter Gas + Gas Galaxies Key
51 Merger Scenario
Momentum
N S
Momentum
Dark Dark Matter
Matter Gas + Gas Galaxies Key
52 Merger Scenario
N C S
Dark Dark Matter
Matter Gas + Gas Galaxies Key
53 MUSKET BALL CLUSTER
54 Musket Ball Cluster
Hubble Space Galaxy Telescope Density Image: STScI Contours Subaru 8m zphot = 0.53±0.1 Telescope Image: Subaru Telescope, NAOJ
KPNO 4m Mayall Telescope Image: NOAO/AURA/NSF
Keck 10m Telescope Image: Laurie Hatch
55 Dawson et al. (2012a) Weak Gravitational Lensing Mass Map
Mass Map Hubble with Space Telescope Galaxy Density Image: STScI Contours (white) Subaru 8m Telescope Image: Subaru Telescope, NAOJ
HST
56 Dawson et al. (2012a) X-ray Gas Map
Chandra Space Telescope Credit: NASA/CXC/Berry
57 Dissociative Merger
N C S
Dark Dark Matter
Matter Gas + Gas Galaxies Key
58 4 ways to constrain sDM with dissociative mergers
• Gas and dark matter offset
≠ 0 ≠ 0
Dark Dark Matter
Matter Gas + Gas Galaxies Key
59 Significant DM-Gas Offset
enables sDM constraint Mass Map Weak lensing with peaks to X-ray Galaxy Density peak offset: Contours (white) and 1.4′ ± 0.3 X-ray contours (red) Following work of Markevitch et al. 2004 휎퐷푀 푐푚2 ≲ 7 푔 푚퐷푀
60 4 ways to constrain sDM with dissociative mergers
• Gas and dark matter offset ≠ 0 • Slowing of the subclusters
• M/L ratio of subclusters ≠ 0
Dark Dark Matter • Galaxies and dark matter Matter Gas + Gas Galaxies
offset Key
61 The Musket Ball mass & galaxy maps generally agree, but…
• Surface mass density 6.5 • S/N map
4.5 • Galaxy density • (white contours) 2.5
0.5
• Centroid errors; Surface Mass Density Density S/NMass Surface • 68%, 95% Confidence -1.5 • (black contours) -3.5
62 The Musket Ball shows an offset between galaxies and WL
6.5
4.5
Weak Lensing Centroid
2.5
0.5
19” Surface Mass Density Density S/NMass Surface -1.5 Galaxy Centroid
-3.5
63 We are improving the dark matter constraint by studying more systems
Galactic light Total mass X-rays Radio waves
500 kpc
Golovich+ 2017
Benson+ 2017
64 Dark Matter Activities
Carolyn Slivinski
65 ACTIVITIES
66 Energy Distribution of the Universe
Energy Distribution of the Universe
Dark Matter, 24%
Ordinary Dark Energy, Atomic Matter, 71.4% 4.6%
Based on http://chandra.harvard.edu/resources/flash/univ_pie.html
67 Paper Plate Activity – Find the Hidden Mass
Use a screwdriver to poke a hole in the center of 2 paper plates, then separate the plates. Arrange 6 quarters symmetrically across the center line of one paper plate.
Add a 7th quarter in a random location, then tape or glue the second paper plate on top.
Use the screwdriver to spin the plate. One side should tilt down. Try to find a location for an 8th quarter on the top plate which will balance the spinning plate (tape it down so it’s firmly attached!). Then measure and mark a location that is located opposite from that 8th quarter. The 7th quarter should be underneath that mark!
Check your results by holding the plates up to a strong light.
This activity is based on materials created by Sonoma State University. 68 “Gravitational lensing” – using an image
Abell 370
69 “Gravitational lensing” – using a light source
Credit: Phil Marshall 70 Wineglass stem Black Hole mass
Magnification Magnification Distortion Distortion
71 ASTC partnership
A Professional Development opportunity – How to Use NASA Resources; future funding resources available
• Seven webinars to be held in 2018, with these goals: • Increase knowledge of NASA Astrophysics-related concepts • Improve familiarity of NASA Astrophysics resources and ways to use them • Utilize real NASA data • Interact with NASA Subject Matter Experts • To participate in this webinar series, contact Wendy Hancock at [email protected] or Tim Rhue at [email protected] by December 31, 2017
As a follow-on to this webinar series, there will be an opportunity to apply for $2,500 mini-fund resources to be competitively awarded to selected institutions, in order to implement or facilitate programming, produce exhibits, etc., using Universe of Learning resources. 58 To ensure we meet the needs of the education community (you!), NASA’s UoL is committed to performing regular evaluations, to determine the effectiveness of Professional Learning opportunities like the Science Briefings. If you prefer not to participate in the evaluation process, you can opt out by contacting Kay Ferrari
This product is based upon work supported by NASA under award number NNX16AC65A to the Space Telescope Science Institute, working in partnership with Caltech/IPAC, Jet Propulsion Laboratory, Smithsonian Astrophysical Observatory, and Sonoma State University. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration.
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