ESA's XMM-Newton, the most sensitive X-ray telescope ever launched, has dramatically changed our view of the most extreme parts of the universe. Although XMM-Newton has travelled some 600 million kilometres, the X-ray telescope is still functioning superbly. With the help of this veteran space telescope astronomers have made crucial observations that have influenced every aspect of astronomy. For example, they have mapped clusters of galaxies, the largest structures in space, and they have investigated areas close to black holes in our galaxy and super-heavy black holes at the centres of other galaxies. As a result of this we now know far more about how super-heavy black holes evolve and how they determine the development of the largest galaxies in the universe. Thanks to XMM we also know far more about how exploding stars produce and scatter chemical elements.
Black holes blow bubbles
The reflection grating spectrometer (RGS) developed by SRON on-board XMM has played an important role in several scientific breakthroughs. For example, in solving the 'cooling flow problem'. Astronomers had long thought that the gas at the centre of a cluster of galaxies would be much colder than its surroundings due to cooling. They suspected that collisions of the hot gas particles would produce large quantities of X-rays that would convey a lot of energy into space. Consequently the gas would cool and contract slightly, resulting in cool gas flowing to the centre: a cooling flow. However using the measurements from the RGS, SRON astronomers demonstrated that the centre of the clusters do not contain a lot of cool gas after all. This being the case, there had to be a heat source somewhere. This ultimately turned out to be the black holes that blow enormous bubbles, thus heating up the gas.
Bumps in emission lines
A second breakthrough was the discovery of strange 'bumps' in the soft X-ray band of a number of active galaxies. Before astronmomers thought that these bumps were the result of absorption by gas clouds outside the centre of these galaxies. Thanks to the high spectral resolution of the reflection grating spectrometer it could now be demonstrated that these emission 'bumps' were caused by gas in the very core of the galaxies, near the central black hole. This has considerably enriched our view of the innermost parts of active Milky Way cores. For the first time SRON astronomers also saw 'fingerprints' of interstellar dust in the X-ray spectra. The fingerprint of these dust particles can reveal more about the composition and evolution of the particles.
Back in 2008, SRON astronomers also managed to identify part of the hidden 'normal' matter in the universe. Just five percent of the universe consists of matter that we are familiar with: protons and neutrons that together with electrons form the atoms from which stars, planets and life are built. Yet half of this matter was quite simply missing. With the help of observations from XMM it was possible to render the hidden 'normal' matter visible. It is distributed through the universe as a web of thread-like structures of rarefied gas and dark matter: the cosmic web.
XMM-Newton is still one of the most important space telescopes in use and one of the most successful space missions. Observations from the space telescope have led to the publication of more than 2000 scientific articles. The observation instruments are still in a good condition and scientists expect that more groundbreaking scientific discoveries will be made with the telescope. Nevertheless, SRON is already working on one of XMM's successors, ASTRO-H.The scientific results from the large X-ray telescopes XXM and Chandra, both of which have been in service for about 10 years, will take centre stage at a scientific congress to be held in Utrecht from 15 to 17 March 2010. The theme of the conference is: High-resolution X-ray spectroscopy: past, present and future.