Gas, dust and stars: the life cycle of galaxies

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The Universe is in constant evolution. Stars form out of clouds of gas. They live by burning hydrogen into helium, and later into carbon and oxygen. The nuclear burning takes place in the centre of the stars, but the products are brought to the surface and change the composition of the star. At the end of its life, the star will expel half or more of its mass in a catastrophic wind. The material blown off from these evolved stars forms fantastic and beautiful structures (e.g. Planetary Nebulae), we don't fully understand the physics that generates the structures but suspect that binary systems and magnetic fields are a factor. The wind expels the newly formed elements into space where they enrich clouds of gas. Thus, the next generation of stars will benefit from these new elements. At the same time, some elements condense as small particles, forming dust grains. These grains are also added to the clouds. When new stars form from this cloud, some of this dust will start the formation of planets. We are studying this cycle of evolution of stars, dust and gas. We study the input of new dust into the interstellar medium, looking at a variety of objects, with special emphasis on conditions of low metallicity, as existed in the early Universe. We study how stars form, especially stars more massive than the Sun. We look at the properties of dust over a complete galaxy (the Large Magelanic Cloud is the main target). We also study the chemistry of interstellar and circumstellar gas. We are also trying to understand how the presence of binary systems can affect the physics of the mass-loss process. The solar system is itself the result of this Universe of evolution. Dust left over from its formation is still present, incorporated in large grains or even comets and meteorites. Space craft are now collecting this dust. One of the goals of our research is to find the progeny of the proto-solar dust, among the outflows of other stars.