Planet and star formation
The idea of stars forming from the collapse of clouds of gas and dust, and of planets forming in disks around these nascent stars, can be traced back to Immanuel Kant in the mid-18th century.
But a closer look reveals that the formation process is anything but simple.
How does interstellar matter condense into these collapse-prone clouds in the first place? Which roles are played by external pressure, magnetic fields, and turbulence, respectively? How do protoplanetary disks form?
How does yet-to-become-planetary-matter clump from microscopic scales to large bodies whose motion is dominated by gravity? What is the role of planets migrating from one part of the disk to another?
Over the last decade or so, progress in observational techniques has allowed astronomers to find answers to at least some of the open questions.
New high-resolution images (see image top right) have begun to show protoplanetary disks of gas and dust in unprecedented detail.
The Herschel Space Telescope (active 2009-2013) and the submillimeter/millimeter telescope ALMA (completed in 2013) have allowed researchers to trace interstellar dust and gas as closely as never before.
This has allowed e.g. for detailed reconstructions of the structure of the dark clouds in which new stars can form (see image left), as well as the identification of the earliest known examples for regions of slightly higher density that have only just begun their collapse.
To understand the underlying physical mechanisms, we run computer simulations, taking into account key factor such as gravity, hydrodynamics effects including turbulence, and magnetic fields. The protoplanetary disk surrounding a young star is a complex, three-dimensional situation, and detailed simulations are only possible using high-powered supercomputers - and they only give reliable physical results when they stay in contact with the ever more detailed observational data.
Scientists used to have no more than one example for a planetary system - our own. Now, with more than a thousand known exoplanets, the data set is much larger. MPIA researchers compare the predictions of planet formation models (e.g. how many Jupiter-like planet of a given mass should there be?) known as "population synthesis" with exoplanet data.