David Helfand

 
David Helfand, Quest University Canada and Columbia University
X-ray Views on the Physics of the Universe

Over the past sixty years, our ability to transcend the atmospheric filter that limits our view of the Universe has allowed us to open dozens of octaves of the electromagnetic spectrum for astronomical observations. I will begin with a musical analogy for this phenomenon and then focus in the 0.1-100 keV portion of the spectrum. From the first V-2 rockets that detected the Sun's X-rays on photographic film to the sub-arcsecond imaging of the Chandra Observatory, the last six decades have seen a greater improvement in both angular resolution and sensitivity in the X-ray band than did the 400 years between Galileo's telescope and Hubble. Physical principles from optics, atomic and molecular physics, photon counting, and kinematics are illustrated in this history. The objects we observe in the high energy universe provide an even richer source of the manifestations of physics on cosmic scales: magnetic reconnection that heats the solar corona, the fluid dynamics of accretion disks, the general relativistic phenomena seen in neutron stars and black holes, the nuclear physics of stellar evolution, the hydrodynamics of supernova explosions, the thermal physics of hot gases from the interstellar to the intergalactic medium, and the striking illustration of dark matter in colliding galaxy clusters may all be used to explicate physics, much of which cannot be reproduced on a laboratory scale.