Public talk given to undergraduates at Eastern Illinois University in February 2014.

1. Bullets and Wine Glasses:
The Exciting Encounters of
Galaxy Clusters
John ZuHone
NASA/Goddard Space Flight Center

2. The Big Bang
• Universe out
“of nothing”
• ~13.8 billion
years ago

3. General Relativity
• Albert Einstein, 1916
• Matter and energy cause
“dents” and “warps” in
the space and time of the
universe, which causes
gravity
• Einstein found that when
he applied his equations
to the entire universe, it
implied the universe had a
beginning (which he didn’t
like)

4. The Expanding
Universe
• Expansion of the universe
• In the late 1920’s Edwin
Hubble measured the
distances to galaxies
• The further away a
galaxy was, the faster it
was moving away
• This implies universal
expansion

5. Redshift

6. Einstein Was Convinced
Einstein
Hubble
Walter Adams
Saurabh W. Jha
(Rutgers)
v = H0d

7. Cosmic Background
Radiation
• Another key evidence:
• If there was a Big Bang, it
should have been very hot and
very dense in the beginning
• This means that the radiation
from that hot period should
still be here
• Today, this radiation is in the
form of microwaves
• Discovered by Penzias and
Wilson in 1965

8. Cosmic Background
Radiation
Seeds of
structure
formation
Planck Satellite, 2013

9. The Formation of Structure
Andrey Kravtsov (U. Chicago)

10. Galaxy Clusters
• Fascinating objects!
• Big: ~10
14
M⊙, ~10
6
ly
• Galaxies: star formation,
supernovae, active galactic
nuclei
• Intracluster medium:
diffuse (<1 atom per cubic
centimeter),
hot (hundreds of millions of
degrees), magnetized plasma
• Dark Matter: makes up the
majority of the mass, only
interacting by gravity

11. Chandra (NASA) XMM-Newton (ESA)
ASTRO-H (JAXA)
Athena (ESA)

12. Galaxies in Visible Light
Abell 1689
Virgo Cluster

13. X-Rays Reveal Cluster Gas
Perseus Abell 520 “El Gordo”
http://chandra.harvard.edu

14. “But what about that ‘dark matter’
stuff? You said you can’t even see
it! How do you know it’s there?”

15. Dark Matter
Fritz Zwicky
Abell 2744
Virial
Theorem:
kinetic energy
potential energy
cluster mass
cluster radius
Newton’s
gravitational
constant
average galaxy speed
10x more
matter than
we can see!!

16. Gravitational Lensing
Again, implies 10x more
mass than we can see

17. Tools of the Trade: High-
Performance Computing
Hardware Software

18. Massive Computing
Hardware
• Thousands, tens of
thousands, hundreds of
thousands of processors
• NASA, NSF, DOE, etc…
• On a somewhat smaller
scale, private companies
are providing similar
access to consumers
(Amazon, Google,
Microsoft, etc.) Blue Gene/P at
Argonne National Laboratory
in Chicago

19. Sophisticated Physics
Software
• Computer simulations of gas
and particle physics
• Hundreds of millions of cells,
billions of particles
• Calculations spread out
across the processors in a
(mostly) balanced fashion

20. A Key Trick: Adaptive Mesh
Refinement

21. The Formation of a Cluster

22. The Bullet Cluster
Dark Matter
Hot Gas
Galaxies
Maxim Markevitch (NASA) and Doug Clowe (Ohio U.)

23. Shock Fronts/Waves
• A wave in a gas that is faster
than the speed of sound in
that gas
• Behind the shock wave, the
gas is denser, and hotter

24. The Bullet Cluster
Bullet
Shock
Turbulence

25. Bullet Cluster
TemperatureX-ray Emission

26. How Much Energy?
• Kinetic energy of a bullet shot from a 9 mm pistol:
• about 500 Joules
• or burning a 100-Watt light bulb for about 5 seconds
• Kinetic energy of the gas “bullet” in the Bullet Cluster:
• about 4 × 1063 Joules
• or about 1061 9 mm bullets
• or about 1050 atomic bombs

27. Dark Matter

28. Hot Gas

29. The “Smoking Gun” for Dark
Matter

30. Sloshing

31. Sloshing

32. Sloshing
Dark Matter
Gas

33. Sloshing

34. Sloshing
Temperature Magnetic Field

35. Sloshing
Sloshing stirs up the
cluster gas, accelerating
high-energy electrons
which spiral around the
magnetic field and radiate
in radio waves
Simona Giacintucci (U. Maryland)

36. Important!
• Why do these analogies work as well as they
do?
• Because the laws of physics are the same
everywhere in the universe.
• The scales and the materials may be different,
but the basic physics is the same!

37. My Own Trajectory
• Undergraduate: University of Illinois at Urbana-Champaign
• Physics major
• Research at U. Illinois, U. Chicago
• Graduate: University of Chicago
• Astronomy and Astrophysics Program
• Computational Science Graduate Fellowship
• Postdoctoral Research
• Harvard University
• NASA
This took: persistence,
support from friends and
family, connections, and
a little bit of luck.

38. Thinking About a Career?
• Some bits of advice…
• Learn to program: C, C++, Fortran, Python, etc.
• Do undergraduate research. You can apply at
many places!
• Find something that interests you. Read about
it. Ask people about it. (Find reputable scientists
on social media and ask them questions!)

39. Thinking About a Career?
• Some bits of advice…
• Don’t give up. It will be hard. It will take lots of time.
But, if you love it, it’s worth it.
• Have a life outside of science. Have friends that
aren’t scientists.
• Be open to career paths outside the norm of
academia: software/hardware support, science
journalism, science consultant for businesses, etc…

40. Website: http://www.jzuhone.com
Twitter: @astrojaz
Google Plus: +JohnZuhone