What is the origin and evolution of stars and planets?

The life cycle of stars is a fundamental topic in astrophysics which is expected to be one of the most active in the coming decades. The cycle of matter from the interstellar medium into stars and then back is the basic engine that drives the evolution of the baryons across the age of the Universe.

Planetary systems like our own will form during the early phases of stellar evolution and the intricate chemistry of the dense interstellar medium around newly formed stars may be a necessary process to produce the complex molecules that are the building blocks for life. Understanding the life cycle of stars is thus a fundamental step to find answers on the origins of our own Solar System and life on Earth as well as for other habitable planets and life elsewhere in the Universe.

The discovery of exoplanets just over a decade ago has opened a new and fascinating front in astrophysics, also for the philosophical implications of the existence of planetary systems outside our Solar System. All extrasolar planetary systems discovered so far are very different from our own, due to the limitations of the techniques used for planet detection. Nevertheless, the discovery of such unexpected configurations has provoked a profound revision of our views of the formation and evolution of planetary systems.

The detection of Earth-like planets and the first search for bio-markers as well as the direct study of planetary systems and analysis of the composition of planetary atmosphere also features prominently in the primary science case for the Extremely Large Telescopes.

Topics that will have to be addressed in the coming decades span a broad range of topics: The role of magnetic fields, gas dynamics including turbulence, multiple systems and clusters in star formation; the detailed shape and possible variations of the initial mass function for stars; the mysteries of the internal structure of stars; the chemical processes in the interstellar medium; the influence of stellar populations on galactic structure; the final stages of stellar evolution and the feedback to the interstellar medium; the evolution of circumstellar discs leading to the formation of planetary systems; the diversity of planetary systems and the search for Solar System analogues.

Key questions will be:

• How do stars form?
• Do we understand stellar structure and evolution?
• What is the life-cycle of the Interstellar Medium and Stars?
• How do planetary systems form and evolve?
• What is the diversity of planetary systems in the Galaxy?
• Is there evidence for Life on exoplanets?