Jelle Kaastra Jelle Kaastra studied astrophysics at Utrecht University. He obtained his Ph.D. in astronomy in 1985 with a thesis on Solar flares. After that he joined the Netherlands Institute for Space Research SRON, first in Leiden, and from 1994 in Utrecht, where he currently is employed as a senior scientist. He is an expert on high-resolution X-ray spectroscopy and currently works on a variety of topics in this field, including clusters of galaxies.