17 - Open issues in small-and large-scale structure formation

Summary

Introduction

This conference has brought together researchers studying structure formation in astrophysics, at scales ranging from planet and star formation through galaxy formation to cosmic structure formation. Aside from gravity, these fields require knowledge about many further physical processes and phenomena, such as turbulent gas dynamics, magnetic fields, non-equilibrium chemistry and the interaction of radiation with matter. The different communities also all rely on numerical simulations and the same modern, general-purpose, ground-based and space-borne telescopes.

In this proceedings contribution, we attempt to identify some of the major challenges for the future. We furthermore debate whether the physical processes relevant for each field exhibit sufficient overlap to warrant concerted cross-disciplinary efforts or whether the features that define and distinguish these fields prevail and make successful cross-fertilization less likely.

Planet formation

With the first discovery of a planet around another star in 1995, we have begun to place our solar system in the context of other planetary systems. More than 250 extrasolar planets have been identified, most with characteristics vastly different from our own solar system. Planets around stars such as our Sun may be the rule, rather than the exception, but the observed properties exhibit an enormous spread (see Udry & Santos 2007).

In the core instability model, planet formation begins with the coagulation of dust in protoplanetary disks, forming larger aggregates of solid material through a sequence of collisions and agglomeration.