Dr Simona Murgia UC Irvine Dr Will Dawson Lawrence Livermore National Laboratory Carolyn Slivinski STScI Facilitator Dr Emma Marcucci STScI Science Briefing October 5 2017 ID: 657572
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What Lurks in the Dark?
An Exploration of Dark Matter
Dr. Simona
Murgia
(UC, Irvine)
Dr. Will Dawson (Lawrence Livermore National Laboratory)Carolyn Slivinski (STScI)Facilitator: Dr. Emma Marcucci (STScI)
Science Briefing
October
5
, 2017Slide2
Additional Resources
2
http://nasawavelength.org/list/1929
Dark Matter Day:
Primary WebsiteFeatured Activities:Jelly Bean UniverseFind the Missing Mass – paper plate activity“Gravitational lensing” with a wine glass
Basic Dark Matter Facts: Chandra Field GuideAsk an AstrophysicistBlog (archived)NASA’s Frontier Fields
Additional Activities:
Dark Matter Possibilities
What’s the Matter?Slide3
Searching for Dark Matter with
Gamma Rays
3
Simona Murgia
University of California, IrvineSlide4
Evidence for Dark Matter:
A Brief Overview
Evidence for dark matter is found at very different scalesGalaxies
Clusters of galaxiesUniverse
4Slide5
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!
Dark matter makes up for the missing mass
F. Zwicky, Astrophysical Journal, vol. 86, p.217 (1937)gasDMCluster
stars
Velocities ~ 1000 km/s
R ~
Mpcs
Distance ~100
Mpc
(1 pc = 3.26 light
yrs
)
Virial theorem: relates the velocity (dispersion,
σ
) of galaxies at some distance
r
from the cluster center to the enclosed mass
M
tot
(r)
Galaxy cluster:
~1-2% stars, ~5-15% gas
;
the rest is dark matter
5Slide6
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 approximately constant, i.e. stars and gas move faster then predicted!
Rotational speed
Distance from centerAndromeda galaxyand therefore:i.e. decreasing with r
6Based on Newtonian dynamics, the velocity (v) of stars and gas in the galaxy should decrease with the distance (r) from the center of the galaxy.Slide7
To reconcile theory with observations, postulate the existence of mass density
not steeply falling as luminous matter density!
Stellar bulge
Gas
Stellar diskDark matterCorbelli et al (2009)
Stars+gas: 1.4 ×1011M⊙ Total mass: 1.3×1012M⊙ ~10 times more dark matter than luminous matter
By adding this extended matter halo, we find good agreement with observations
e
.g
. Andromeda galaxy
therefore:
Assume additional mass:
and finally:
Dark matter makes up
for
the missing mass
Andromeda galaxy
Rotation Curves of Galaxies
7Slide8
Cosmic Microwave Background
Require additional matter to
start forming structure earlier
T = 2.725 K
ΔT ~ 200 μKVery small temperature fluctuations, too small to evolve into structure observed todayPlanck 2015Dodelson et al 2006Power spectrum of matter fluctuations
baryons onlysmaller scalesClumpiness
larger scales
Observed (SDSS)
8
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 Slide9
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
is neutralis stable (or it is very long-lived)
But not what it is...9Slide10
Dark Matter Candidates
Need new particles and new theories beyond the Standard Model of particle physics!
None of the known elementary particles has the right properties to be
the dark matter
Image credit: G. Bertone10Slide11
Dark Matter Searches
COLLIDER SEARCHES
Large Hadron Collider
Dark Matter
Standard ModelDIRECT SEARCHES
CDMSXENON100
INDIRECT SEARCHES
PAMELA
Fermi-LAT
IceCube
Dark Matter
Dark Matter
Standard Model
Standard Model
Produce it in the lab
Find its annihilation
byproducts
Detect energy it deposits
11Slide12
Indirect Dark Matter Searches
Via
Lactea
II (Diemand et al. 2008)
+12DARK MATTER DISTRIBUTIONANNIHILATION PROCESSVery rich search strategy, multi-messenger and multi-wavelengthGamma rays are particularly good probes to learn about the particle nature of dark matter via its annihilations
Simulated Milky Way-like dark matter halo:very dense at its center, large number of substructures 12Slide13
Gamma rays from Dark Matter
Annihilation
Pieri et al, arXiv:0908.0195
Galactic centerDark matter substructures
13Slide14
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
Dark matter particle mass
Annihilation cross section
(how often annihilations occur)Detection!14Slide15
Dark matter particle mass
Annihilation cross section
(
how often annihilations occur)Indirect Detection Results - Gamma Ray
If a signal is not detected, we can rule out many possibilitiesRuled outAllowed15Slide16
Fermi MissionThe Large Area Telescope
Orbit: 565 km,
25.6o inclination, circular. The LAT observes the entire sky every ~3 hrs (2 orbits)
The Fermi Large Area Telescope (LAT) observes the gamma-ray sky in the 20 MeV to >300 GeV energy range with unprecedented sensitivity
Fermi LATFermi LAT is a pair conversion telescope: gamma ray converts to electron-positron pairs which are recorded by the instrument
16Slide17
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
17Slide18
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 inferredHowever, other more mundane gamma-ray sources such as pulsars could explain the excessImage credit: NASA/T. Linden, U. ChicagoC. Karwin et al, arXiv:1612.05687
Annihilation cross sectionDark matter particle mass18Slide19
Caveats
=
+
+
datasourcesgalactic interstellar emissionisotropic+
dark matter??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!
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!)
19Slide20
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
Dark Matter Substructures20Slide21
Dwarf Spheroidal Galaxies
Dark matter particle mass
Annihilation cross section
Ruled out
AllowedThe limits probe a dark matter explanation of the Galactic center excessSearch for a signal in 25 dwarf spheroidal galaxies. No significant emission is found
21Fermi LAT Collaboration, arXiv 1503.02641Slide22
Dwarf Spheroidal Galaxies
Fermi LAT Collaboration,
arXiv
1503.02641
The limits probe a dark matter explanation of the Galactic center excessDark matter particle massAnnihilation cross sectionDark matter interpretation of Galactic center excess
Search for a signal in 25 dwarf spheroidal galaxies. No significant emission is found
22Slide23
Summary/Outlook
Evidence for dark matter is overwhelmingMany experiments have been relentlessly searching for dark matter particle candidates
Gamma rays have been able to test and rule out many possibilitiesAn 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!
23Slide24
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, LLCSlide25
Galaxy ClusterMass ~ 1015 Solar Masses
Abell 1689
NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM)
25Slide26
Most people are familiar with
Credit: NASA CXC26Slide27
Astronomer’sPeriodic Table
Credit: NASA CXC27Slide28
A new component to clusters
28Slide29
Accelerating electronsemit photons
29Slide30
Chandra X-ray Map of the Cluster Plasma
Abell 1689
X-ray: NASA/CXC/MIT/E.-H Peng et al; Optical: NASA/STScI
30Slide31
Far more of the mass is in the X-ray emitting intracluster plasma
31Slide32
Cosmologist’sPeriodic Table
DarkMatter
32Slide33
Gravitational lensingbest tool for studying dark matter
Zwicky (1937)
33Slide34
Mass warps space-time andalters the path of light
34Slide35
Gravitational lensingdistorts galaxy images
35Slide36
36Slide37
37Slide38
38Slide39
39Slide40
Gravitational lensing of clustersnot observed until 1990
Tony Tyson40Slide41
Weighing clusters with weak gravitational lensing
Tyson et al. (1990)Abell
168941Slide42
The first gravitational lensingmass map
Tyson et al. (1990)Abell
168942Slide43
Thanks to Hubble a lot has improved in past 20 years
Abell 1689
NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM)
43Slide44
Much higher resolutionmass maps
Abell 1689
NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM)
44Slide45
Abell
1689X-ray: NASA/CXC/MIT/E.-H Peng et al; Optical: NASA/STScI
Abell
1689X-ray PlasmaDark Matter
NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM)45For some clusters the X-ray plasma and dark matter distributed similarly Slide46
Merging galaxy clusters are an exception
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.
Bullet Cluster46Slide47
Merger Scenario
Key
Dark Matter
Gas
Dark Matter+ GasGalaxiesSN
47Slide48
Merger Scenario
Key
Dark Matter
Gas
Dark Matter+ GasGalaxiesSN
Gravitational Attraction
48Slide49
Merger Scenario
Key
Dark Matter
Gas
Dark Matter+ GasGalaxiesSN
49Slide50
Merger Scenario
Key
Dark Matter
Gas
Dark Matter+ GasGalaxiesSN
50Slide51
Merger Scenario
Key
Dark Matter
Gas
Dark Matter+ GasGalaxiesN+S51Slide52
Merger Scenario
Key
Dark Matter
Gas
Dark Matter+ GasGalaxies
N
S
Momentum
Momentum
52Slide53
Merger Scenario
Key
Dark Matter
Gas
Dark Matter+ GasGalaxies
NS
C
53Slide54
Musket Ball Cluster54Slide55
Musket Ball Cluster
Galaxy Density
Contourszphot
= 0.53±0.1Dawson et al. (2012a)
55Slide56
Weak Gravitational Lensing
Mass Map
HSTDawson et al. (2012a)
Mass Mapwith
Galaxy Density Contours (white)56Slide57
X-ray
Gas Map
57Slide58
Dissociative Merger
Key
Dark Matter
Gas
Dark Matter+ GasGalaxies
N
S
C
58Slide59
4 ways to constrain
sDM with dissociative mergers
Key
Dark Matter
GasDark Matter+ GasGalaxies
Gas and dark matter offset
59Slide60
Significant DM-Gas Offsetenables sDM constraint
Weak lensing peaks to X-ray peak offset:
Following work of Markevitch et al. 2004
Mass MapwithGalaxy Density Contours (white)andX-ray contours (red)
60Slide61
4 ways to constrain sDM with dissociative mergers
Key
Dark Matter
Gas
Dark Matter+ GasGalaxiesGas and dark matter offsetSlowing of the subclustersM/L ratio of subclustersGalaxies and dark matter offset
61Slide62
4.5
2.5
0.5
-
1.5-3.56.5Surface Mass Density S/NThe Musket Ball mass & galaxy maps generally agree, but…Surface mass density S/N mapGalaxy density(white contours)Centroid errors;68%, 95% Confidence (black contours)62Slide63
4.5
2.5
0.5
-
1.5-3.56.5Surface Mass Density S/NThe Musket Ball shows an offset between galaxies and WL
19”Weak Lensing CentroidGalaxy Centroid
63Slide64
We are improving the dark matter constraint by studying more systems
Galactic light
Total mass
X-raysRadio waves
Golovich+ 2017Benson+ 201764Slide65
Dark Matter Activities
65
Carolyn
SlivinskiSlide66
66
Jelly
Bean
Universe Paper
Plate Activity Wine Glass demonstrationACTIVITIESSlide67
67
Energy Distribution of the Universe
Based on
http://
chandra.harvard.edu/resources/flash/univ_pie.htmlSlide68
68
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 7
th 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.Slide69
69
“Gravitational lensing” – using an image
Abell 370Slide70
70
Credit: Phil Marshall
“Gravitational lensing”
– using a light sourceSlide71
71
Wineglass stem
Black Hole
massMagnificationDistortion
MagnificationDistortionSlide72
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 conceptsImprove familiarity of NASA Astrophysics resources and ways to use themUtilize real NASA dataInteract with NASA Subject Matter Experts
To participate in this webinar series, contact Wendy Hancock at whancock@astc.org or Tim Rhue at trhue@stsci.edu by December 31, 2017As 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.
58Slide73
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 <kay.a.ferrari@jpl.nasa.gov>.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.73