Laboratory Astrophysics: An Indispensable Tool for Unraveling the Secrets of the Universe; Solar Wind Charge Exchange X-Ray Emission in the Solar System as a Case Study

Speaker: Dr. Rami Ali, Visiting Professor at American University of Sharjah, UAE

Abstract 

Since the discovery of a dazzlingly bright X-ray emission from Comet Hyakutake in 1996 by the German Satellite ROSAT, X-ray emissions from over 30 comets haven been detected by NASA’s Chandra and ESA’s XMM-Newton space-based orbiting X-ray observatories.  Charge exchange between highly charged solar wind ions and cometary neutrals is the primary mechanism behind these emissions. In solar wind charge exchange (SWCX), electrons are captured from cometary neutrals by the solar wind ions into excited states, which may emit X-rays while decaying. Observations have also shown that SWCX contributes to X-ray emission from planetary atmospheres, and to the soft X-ray background of the heliosphere via interactions with the neutral interstellar medium (ISM), and suggested that charge exchange could be a significant contributor to X-ray emission in supernova remnants and starburst galaxies.

While SWCX proved to be a powerful new tool for space physics studies, the 2019 first issue of The Astronomy and Astrophysics Reviews labeled it an astrophysical nuisance, being present in every X-ray observation of an astrophysical object. It is a serious impediment to the study of the diffuse hot ISM, and its modeling, in order to remove it from astrophysical observations, has proven to be more difficult than originally anticipated. The problem is interdisciplinary and requires the collective efforts of the astrophysics, heliophysics, space and planetary physics, theoretical atomic physics, and laboratory astrophysics communities.

This seminar will illustrate the crucial role played by laboratory astrophysics in uncovering and improving our understanding of the salient features underlying SWCX interactions, and in providing vital atomic data for benchmarking atomic theories and emission models. Highly differential studies simulating SWCX interactions by means of simultaneous cold-target recoil ion momentum (COLTRIMS) and X-ray spectroscopic techniques will be presented. This powerful reaction microscope allowed the scrutiny of SWCX at an unprecedented level of detail, and provided unequivocal evidence for the significance of multiple-electron capture to cometary and planetary X-ray emissions. Obtained state-selective X-ray spectra continue to critically test theories at the quantum level.

About the Speaker

Professor Rami Ali is currently a visiting professor at the Department of Physics of American University of Sharjah. He earned his PhD in experimental atomic physics from Kansas State University, USA, in 1993. He was a postdoctoral fellow at Argonne National Laboratory, USA, and has 23 years of undergraduate and graduate teaching experience at American University of Sharjah; University of Nevada, Reno; Hashemite University, Jordan; and the University of Jordan, where he also served 10 years as its International Affairs Unit Director, becoming an expert on internationalization of higher education. His research concerns interactions of ionizing radiation with matter, particularly the interactions of low energy highly charged ions with atoms and molecules of relevance to astrophysical and fusion plasmas.

For more information, contact nabdulmaati@aus.edu.