Dark Matter in Galaxy Clusters: Past, Present, and Future...
Transcript of Dark Matter in Galaxy Clusters: Past, Present, and Future...
![Page 1: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/1.jpg)
Uranus Mercury Dark matter Mergers
Dark Matter in Galaxy Clusters:Past, Present, and Future
David WittmanUniversity of California, Davis
National Astronomy Teaching Summit 2016
![Page 2: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/2.jpg)
Uranus Mercury Dark matter Mergers
Dark matter or modified gravity: case study #1
Discovered Uranus 1781
![Page 3: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/3.jpg)
Uranus Mercury Dark matter Mergers
Uranus’ orbit: poor fit to Newtonian model of solar system
Suggested causes of poor fit:
• Unseen matter: unseen planet perturbing Uranus
• Modified gravity: inverse-square law may fail at largedistances
Auxiliary assumptions
Unifying theory
Another option: reject discrepant data
![Page 4: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/4.jpg)
Uranus Mercury Dark matter Mergers
Uranus’ orbit: poor fit to Newtonian model of solar system
Suggested causes of poor fit:
• Unseen matter: unseen planet perturbing Uranus
• Modified gravity: inverse-square law may fail at largedistances
Auxiliary assumptions
Unifying theory
Another option: reject discrepant data
![Page 5: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/5.jpg)
Uranus Mercury Dark matter Mergers
Uranus’ orbit: poor fit to Newtonian model of solar system
Suggested causes of poor fit:
• Unseen matter: unseen planet perturbing Uranus
• Modified gravity: inverse-square law may fail at largedistances
Auxiliary assumptions
Unifying theory
Another option: reject discrepant data
![Page 6: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/6.jpg)
Uranus Mercury Dark matter Mergers
Uranus’ orbit: poor fit to Newtonian model of solar system
Suggested causes of poor fit:
• Unseen matter: unseen planet perturbing Uranus
• Modified gravity: inverse-square law may fail at largedistances
Auxiliary assumptions
Unifying theory
Another option: reject discrepant data
![Page 7: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/7.jpg)
Uranus Mercury Dark matter Mergers
Are these options equally likely?
Consider:
• inverse-square law explains an enormous array of other data
• clues from residual pattern
• simplicity of hypotheses (Occam’s razor): physics may be theonly class your students are exposed to this!
![Page 8: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/8.jpg)
Uranus Mercury Dark matter Mergers
Resolution: unseen massUrbain Le Verrier predicted position and massof unseen planet in 1846—it was discoveredafter one hour of searching near predictedposition.
![Page 9: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/9.jpg)
Uranus Mercury Dark matter Mergers
Case study #2: Mercury precesses too much
• “Normal” precession: 0.15◦/century
• “Anomalous” precession: 0.012◦/century
![Page 10: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/10.jpg)
Uranus Mercury Dark matter Mergers
Hypotheses
• Unseen matter: unseen planet (“Vulcan”) orbiting near Sun
• Modified gravity: steeper than inverse-square? Tinker withspeed?
Which seems more likely?
![Page 11: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/11.jpg)
Uranus Mercury Dark matter Mergers
Surprise resolution
By 1915 general relativity explained the anomalous precession.
![Page 12: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/12.jpg)
Uranus Mercury Dark matter Mergers
What if we found orbital mismatcheseverywhere in the universe?
![Page 13: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/13.jpg)
Uranus Mercury Dark matter Mergers
Zwicky (1935): Galaxy Cluster Dynamics
![Page 14: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/14.jpg)
Uranus Mercury Dark matter Mergers
“Dark Matter” Dynamics: Everywhere You Look
http://wittman.physics.ucdavis.edu/
Animations/RotationCurve/
• rotation curves ofspiral galaxies
• σv of ellipticalgalaxies
• X-rays from galaxyclusters
• galaxy mergers
• structure formation
• cosmic microwavebackground
![Page 15: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/15.jpg)
Uranus Mercury Dark matter Mergers
Gravitational lensing
Probes the mass distribution independent of dynamical state andwithout normal-matter tracers.
Credit: New York Times
![Page 16: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/16.jpg)
Uranus Mercury Dark matter Mergers
Gravitational lensing analogies
Credit: Melinda Keller, Oberlin College
![Page 17: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/17.jpg)
Uranus Mercury Dark matter Mergers
Gravitational lensing in action
NASA/HST
NASA/HST
![Page 18: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/18.jpg)
Uranus Mercury Dark matter Mergers
More lensing in action: see alsohttps://www.lsst.org/media/lens-simulations
NASA/HST
![Page 19: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/19.jpg)
Uranus Mercury Dark matter Mergers
More lensing in action: SN Refsdal
NASA/HST
![Page 20: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/20.jpg)
Uranus Mercury Dark matter Mergers
More lensing in action: SN Refsdal
NASA & ESA and P. Kelly (UC Berkeley)
![Page 21: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/21.jpg)
Uranus Mercury Dark matter Mergers
Dark matter or modified gravity?
• dark matter is (can be?) an extravagant hypothesis
• but modified gravity struggles to fit so many differentenvironments, e.g. cluster centers vs galaxy outskirts
=⇒ dark matter overwhelmingly favored
Can we prove DM more directly by isolating it from normal matter?
![Page 22: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/22.jpg)
Uranus Mercury Dark matter Mergers
Anatomy of a Merger
Predict where the mass will be found!
Figure credit: Will Dawson
![Page 23: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/23.jpg)
Uranus Mercury Dark matter Mergers
Anatomy of a Merger
Predict where the mass will be found!
Figure credit: Will Dawson
![Page 24: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/24.jpg)
Uranus Mercury Dark matter Mergers
Anatomy of a Merger
Predict where the mass will be found!
Figure credit: Will Dawson
![Page 25: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/25.jpg)
Uranus Mercury Dark matter Mergers
Anatomy of a Merger
Predict where the mass will be found!
Figure credit: Will Dawson
![Page 26: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/26.jpg)
Uranus Mercury Dark matter Mergers
Bullet ClusterClowe et al (2006): “A direct empirical proof of the existence of dark matter”
gas (from X-rays); mass (from grav. lensing)
![Page 27: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/27.jpg)
Uranus Mercury Dark matter Mergers
So what is dark matter? Not protons or neutrons
Big Bang nucleosynthesis argument:
proton
neutron
![Page 28: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/28.jpg)
Uranus Mercury Dark matter Mergers
So what is dark matter? Not protons or neutrons
Big Bang nucleosynthesis argument:
proton
neutron
more protons/neutrons =⇒ less leftover deuterium and more 4He
![Page 29: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/29.jpg)
Uranus Mercury Dark matter Mergers
Big Bang nucleosynthesis: models vs data
observed abundances⇓
too fewprotons/neutrons
⇓DM is something else!
Source: Charbonnel 2002,Nature 415, 27
Also note: CMB
![Page 30: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/30.jpg)
Uranus Mercury Dark matter Mergers
So what is dark matter?
We know what it’s not:
• not made of protons or neutrons
• does not interact with light
=⇒ new particle or particles w/these properties:
• stable (ish)
• “cold” (nonrelativistic)
• collective density ∼ 2× 10−27 kg/m3
• does not interact with SM particles (except perhaps weakly)
Lots of models to test: WIMPs, axions, hidden-sector models....
![Page 31: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/31.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
![Page 32: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/32.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
![Page 33: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/33.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
![Page 34: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/34.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
![Page 35: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/35.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
![Page 36: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/36.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
![Page 37: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/37.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
![Page 38: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/38.jpg)
Uranus Mercury Dark matter Mergers
Unified picture of (most) dark matter searches
Figure credit: Annika Peter, arXiv:1201.3942
But this figure is incomplete...
![Page 39: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/39.jpg)
Uranus Mercury Dark matter Mergers
The drag force awakens
Self-interacting dark matter (SIDM) would transfer momentum ina collision:
Offset in Bullet is consistent with zero =⇒ σSIDM . 2 barn/GeV(Randall+08)
![Page 40: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/40.jpg)
Uranus Mercury Dark matter Mergers
Wait, 2 barns per GeV??
• ∼ 1020 times larger than upper limits on DM interacting withnormal matter
• Incredibly, we don’t yet know whether DM particles interactwith each other at this level
• Some “hidden sector” particle models predict this, and somegalaxy data suggest it
• Only astrophysics can constrain these models!
Can we use clusters as natural colliders to learn more about theDM particle?
![Page 41: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/41.jpg)
Uranus Mercury Dark matter Mergers
Merging cluster collaboration: find/analyze more Bullets!
Figure credits: Will Dawson
![Page 42: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/42.jpg)
Uranus Mercury Dark matter Mergers
Two recent MCC discoveries
ZwCl 0008: a low-mass Bullet
1 Mpc
MACS J1149: a stripped binary merger
1 Mpc
![Page 43: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/43.jpg)
Uranus Mercury Dark matter Mergers
Merging clusters can probe the type of interaction
(1) Frequent interactions w/small momentum transfer—long rangeforce like E&M
(2) infrequent interactions with large momentum transfer—likehard sphere scattering
(3) no interaction
![Page 44: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/44.jpg)
Uranus Mercury Dark matter Mergers
Merging clusters can probe the type of interaction
(1) Frequent interactions w/small momentum transfer—long rangeforce like E&M
(2) infrequent interactions with large momentum transfer—likehard sphere scattering
(3) no interaction
![Page 45: Dark Matter in Galaxy Clusters: Past, Present, and Future ...scalettar.physics.ucdavis.edu/frs/wittmantalk.pdf · Dark Matter in Galaxy Clusters: Past, Present, and Future [scale=0.7]MergingClusterGallerylong.png](https://reader034.fdocuments.net/reader034/viewer/2022050404/5f81ed3c43023263881e8226/html5/thumbnails/45.jpg)
Uranus Mercury Dark matter Mergers
Summary
• the Bullet cluster was the first picture of dark matter withoutits usual camouflage
• nature provides many more!
• these “Large Dark Matter Colliders” will test particle modelsrobustly
Astronomy and physics work together beautifully to reveal unseenaspects of nature.