Bullets and Wine Glasses: The Exciting Encounters of

Galaxy ClustersJohn ZuHone

NASA/Goddard Space Flight Center

The Big Bang

• Universe out “of nothing”

• ~13.8 billion years ago

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)

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

Redshift

Einstein Was Convinced

Einstein

Hubble

Walter AdamsSaurabh W. Jha (Rutgers)

v = H0d

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

Cosmic Background Radiation

Seeds of structure formation

Planck Satellite, 2013

The Formation of Structure

Andrey Kravtsov (U. Chicago)

Galaxy Clusters• Fascinating objects!

• Big: ~1014

M⊙, ~106 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

Chandra (NASA) XMM-Newton (ESA)

ASTRO-H (JAXA) Athena (ESA)

Galaxies in Visible LightAbell 1689

Virgo Cluster

X-Rays Reveal Cluster Gas

Perseus Abell 520 “El Gordo”

http://chandra.harvard.edu

“But what about that ‘dark matter’ stuff? You said you can’t even see

it! How do you know it’s there?”

Dark Matter

Fritz Zwicky

Abell 2744

Virial Theorem:

kinetic energypotential energy

cluster mass

cluster radius

Newton’s gravitational

constant

average galaxy speed

10x more matter than

we can see!!

Gravitational Lensing

Again, implies 10x more mass than we can see

Tools of the Trade: High-Performance Computing

Hardware Software

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

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

A Key Trick: Adaptive Mesh Refinement

The Formation of a Cluster

The Bullet Cluster

Dark Matter

Hot Gas

Galaxies

Maxim Markevitch (NASA) and Doug Clowe (Ohio U.)

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

The Bullet Cluster

BulletShock

Turbulence

Bullet ClusterTemperatureX-ray Emission

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

Dark Matter

Hot Gas

The “Smoking Gun” for Dark Matter

Sloshing

Sloshing

Sloshing

Dark Matter

Gas

Sloshing

Sloshing

Temperature Magnetic Field

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)

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!

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.

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!)

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…

Website: http://www.jzuhone.com Twitter: @astrojaz

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