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 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 ‣ ‣ Clusters of galaxies ‣ Universe

4 Clusters

The existence of dark matter was postulated by Fritz Zwicky in the 1930’s to explain the dynamics of galaxies in the Coma 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% , ~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 : 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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