LECTURE 4

In Lecture 4 we continue with the electromagnetic description of our Universe, moving to the higher temperatures characteristic of the optical and, above all, of the X- ray domain. Of course, the HUBBLE SPACE TELESCOPE has been the workhorse of space astronomy for 15 years, and has yielded high quality, high resolution results from planets to distant galaxies in a band from the near-UV to the optical to the near IR. Its usefulness to astronomy has probably been greater than that of any other telescope in the history of mankind, and a few examples will be given of the different types of work possible with Hubble. One important aspect of Hubble has been the optical identification and characterization of newly discovered X-ray sources. Astronomy with X-rays has been an extremely productive new window on the sky. In the 40 years since the discovery of the first X-ray source, X-ray astronomy has now observed hundreds of thousands of objects, emitting X-rays through a variety of mechanisms. These contain thermal and no-thermal mechanisms, and go from the Moon to planets and comets, to main-sequence stars of all spectral types in our Galaxy to emission from compact galactic objects, both isolated and in binary systems. It also includes detailed studies of nearby galaxies and their stellar content and population, as well as more and more distant galaxies and clusters of galaxies until the cosmological sources merge in the diffuse X-ray background. The incredible story of X-ray astronomy, or at least its most recent chapters, is well traced by the results of few recent telescopes. - ESA’s XMM/NEWTON and NASA’s CHANDRA are now in orbit (and have been for several years), to provide the most productive ever wealth of X-ray results. The two telescopes have different characteristics, but are of equal importance for the advancement of space astronomy. - the future of X-ray astronomy requires novel photon-gathering and detection techniques. CNES and ASI are planning to do a new step in this direction, planning to use the formation-flying technique in the SYMBOL-X mission (2013?) for high energy X-ray focussing. - a much greater grasp is planned for X-ray missions in the post-2015 era. These will also exploit variations of the formation flying techniques, coupled with innovative optics design. A totally new source physics should move within reach with these new generation X–ray telescopes. These are provisionally called XEUS for the ESA mission, and CONSTELLATION-X for NASA. (in all, 6 space telescopes in the X-ray domain will be reviewed)