John R. Peterson

Assoc. Professor of Physics

Purdue University






S2007, S2008, & S2009:  Physics 360, Quantum Mechanics

F2007, F2008, F2009, S2013, S2014, & S2015:  Physics 172, Modern Mechanics

S2010, S2011, S2012, S2022, S2023:  Physics & Astronomy 562, High Energy Astrophysics

F2010, F2011, & F2012:  Physics & Astronomy 561, Galaxies & Large Scale Structure

F2013, F2014, F2015, F2016, F2020, F2021, F2022, F2023:  Astronomy 370, Cosmology

S2016 & S2017:  Physics & Astronomy 563, Particle Astrophysics

F2017, F2018, F2019:  Physics & Astronomy 567:  Observational Techniques in Astronomy

S2019, S2020, S2021:  Physics & Astronomy 560:  Stellar Evolution




Research Fields:  X-ray & Optical Astrophysics, Particle Astrophysics, & Cosmology

Research Subjects:  Clusters of Galaxies, Galaxies, Dark Energy, & Dark Matter


Description: clustergallery



My group focuses on research in astrophysics and cosmology using data from X-ray and optical telescopes.  Some work we have done on the X-ray spectra of clusters of galaxies (above left) demonstrates a discrepancy in a model how the gas in clusters of galaxies cools.  The X-ray spectrum contains a number of atomic emission lines, which act as a thermostat for gas of specific temperatures.  The light blue model is the standard model for complete cooling, but is clearly inconsistent with the observed data (dark blue).  Instead a model where the colder plasma is missing (red) matches the data well.  The interpretation of this is still unclear, since it would seem to indicate an enormous heating source inside the largest structures in the Universe.

By simply counting the number of clusters of galaxies in the Universe and measuring where they are, we have an extremely sensitive indicator of how much dark matter and dark energy there is in the Universe.  The above right image shows a collection of new clusters of galaxies we have found by using the most sensitive X-ray telescopes.  The number and location of the clusters of galaxies in the Universe follows a theory for how fast matter can form structures as the Universe begins to expand.  Thus, this can be used to measure properties of dark matter and dark energy.

Galaxies can be studied in optical images (below) to map the distribution of matter in the Universe.  In addition, gravitational forces that alter the path of light before it reaches us can distort the shapes of distant galaxies.  This is a relatively new technique that can map the dark matter in the Universe.  Furthermore, the recessional velocity of the galaxies can be estimated by using the galaxy colors.  This enables us to map out this dark matter map crudely in cosmic time, since faster moving galaxies are correlated with larger cosmic distances.  It is thought that the evolution of the dark matter map is sensitive to the properties of dark energy.  Thus, detailed measurements of galaxies can help us to unravel the mystery of both dark matter and dark energy.

These dark matter & dark energy measurements, however, are relatively subtle and require careful study of measurement systematics.  Because of that we created a Photon Simulator that uses ab initio physics calculations to simulate light through the atmosphere and then through a telescope and camera system.   All possible distortions of the images of galaxy light through atmosphere+telescope+camera system can then be studied in detailed.  Much more detail about these simulations including movies of aspects of the simulator can be found at the PhoSim website.




Current Group Members:


Post Doctoral Researchers and Research Associates:


                  Glenn Sembroski (Research Associate 2015-)



         Graduate Students:


              Anirban Dutta (Graduate Student 2018-)



Undergraduate Students:



Past Group Members:


         Caleb Remocaldo (2018-2020, Purdue undergraduate)

Colin Burke (2015-2018, Purdue undergraduate, now a graduate student in astronomy at U Illinois)

Kira Graves (2017-2018, Purdue undergraduate)

Mackenzie Geckler (2018, Purdue undergraduate)  

         En-Hsin Peng (2011-2015 Postdoc; Research Associate 2015-2017)

         Jun Cheng (2015-2017, Purdue graduate student, PhD 2017)

Matt Wiesner (2015-2016 Postdoc; Assistant Professor at Benedictine University)

         Mingbin Leng (2013-2014, Purdue undergraduate; now a graduate student in physics at Brown Univ.)

         Amanda Winans (2012, REU student from Missouri State)

         Mary Ann Hodge (2011, REU student from Murray State; now a graduate student in physics at Purdue Univ.)

         Nathan Todd (2009-2011, Purdue undergraduate; now a graduate student in physics at Washington Univ.)

         Mark Hannel (2010-2011, Purdue undergraduate; now a graduate student in physics at NYU)

         Satya Nagarajan (2010-2011, Purdue undergraduate; now a graduate student in physics at Ohio State)

         Zarah Ahmad (2010 REU student from South Eastern Missouri State)

         Mallory Young (2009, REU student from Hendrix Univ.; now a graduate student in seismology at Australian National University)

         Emily Grace (2008-2010 Purdue undergraduate; now a graduate student in physics at Princeton)

         Alexandra Lupu (2007, REU student from Cornell Univ.)

Kari Frank (2007-2013, Purdue graduate student, PhD 2013, research associate at Penn State)

Justin Bankert (2006-2010 Purdue undergraduate; graduate student in physics at Johns Hopkins)

         Alan Meert (2006-2009 Purdue undergraduate; graduate student in physics at U. Penn)

Suzanne Lorenz (2006-2012, Graduate Student, PhD 2012, now lecturer at U Alaska)


Major Software Projects:


X-ray Monte Carlo (XMC):  Detailed X-ray Monte Carlo Simulation Code

                  Photon Simulator (PhoSim):  Detailed Ab Initio Photon Optical/IR Monte Carlo Simulation Code




XMM-Newton Observatory (

Chandra X-ray Observatory (

LSST (Large Synoptic Survey Telescope) (

Suzaku (

Sloan (

Hubble (

Subaru (

JWST (James Webb Space Telescope) (

Dark Energy Survey (DES) (




Biographical Information:




PhD, Physics, Columbia University, 2003

M Phil, Physics, Columbia University, 2000

MA, Physics, Columbia University, 1999

BA Honors, Physics, University of Chicago, 1997


Professional History:


         2012-          Associate Professor of Physics, Purdue University

         2006-2012   Assistant Professor of Physics, Purdue University

         2003-2006  Postdoctoral Research Associate, Stanford University and SLAC

         1997-2003   Graduate Research Assistant, Columbia University

         1994-1997   Undergraduate Research Assistant, University of Chicago and Fermilab