Supervisor: Stefan Meingast (Department of Astrophysics) in collaboration with João Alves (Department of Astrophysics)

Funding Situation: potentially via a VISESS PhD fellowship

Project outline: Star clusters are the building blocks of our Galaxy and to this day, they are thought to be the birthplace of most stars. Recent findings, building on groundbreaking new observations from the Gaia space mission, have raised serious doubts about this fundamental premise: Nearby young star clusters, such as the Pleiades, are found to comprise only the proverbial tip of the iceberg. Instead, these apparent clusters are each surrounded by vast stellar halos, stretching across hundreds of parsecs. Moreover, the immediate solar neighbourhood harbours young, massive stellar streams, previously undetectable due to their vast extent in the sky. The discovery of these cluster coronae and the stellar streams provokes several key questions the PhD student will focus on:

• Dissecting the six-dimensional phase space (positions and velocities): what is the true stellar inventory of the solar neighborhood? What is the extent of the coronae, how many stellar streams are there?
• Star formation vs. galactic dynamics: Nature or nurture? Are the clusters’ coronae and streams a consequence of dynamical evolution or are they an imprint of birth conditions?

To answer these questions and to potentially overthrow the decade-old paradigm whether truly most stars form in clusters, the PhD student will work with astrometric data provided by the Gaia mission, supplemented by kinematics from the ESO survey VISIONS (visions.univie.ac.at). The student will expand and develop sophisticated big data analysis methods and will be part of a vibrant research environment in the group of João Alves at the Department of Astrophysics.