Very hot gases, with temperatures in the range of a million to one hundred million degrees, emit X-rays. These gases are found around stars, quasars, galaxies and clusters of galaxies, in the most exotic and violent phenomena in the Universe. The XMM-Newton observatory will search for and measure the energy from all these types of objects and more. The results will provide a wealth of information about the evolution of the Universe, the extreme physics around black holes in quasars and binary star systems, and the interaction between light and matter at a fundamental level.
Space is the ultimate physics laboratory.
This information is used to determine the nature of the X-ray emitting gas under investigation. For example, it tells astronomers about the temperature of the gas, how it's moving, what elements are present in the gas and how much there is of each element. They are the central engines of the earliest galaxies, approximately the size of our Solar System but emitting so much energy that they outshine the 100 billion or so stars in the surrounding galaxy. Some is thrown out in a jet at velocities close to the speed of light into the most distant reaches of the galaxies, for distances of hundreds of thousands of light years. The MSSL Astrophysics Group's Beginners Guide to AGN has more information about quasars, including details about the structure of the disc, black hole and surrounding gases.