Past Events

Abstract:

The universe is a hierarchy of multi-component self-gravitating systems, from cosmic walls, superclusters, clusters, groups and galaxies to globulars, clouds, stars and sub-stellar objects. Gravity is a long-range force, and gravitational interaction is particularly important in large-scale systems. Self-gravitating objects are known to show a variety of peculiar behaviours. The presence of multiple components further adds complexities to their kinematics and dynamics. Clusters and larger cosmic objects have two fundamental components, dark matter and baryons. Dark matter dominates the inertia but does not participate in electromagnetic processes. The system energy budget is however determined by baryons, through radiative loss. The nature of dark matter is a mystery. We are still uncertain about the number of dark-matter species and whether dark matter is collisional or collisionless. The knowledge of these intrinsic dark-matter properties is essential for establishing the thermodynamics of dark matter and for modelling the global dynamics and structural evolution of the universe.

In this talk I will present my current work on galaxy clusters, and cosmic walls and voids on the framework of self-interacting dark matter and radiative gas. I will show how structures and dynamics of galaxy clusters are dependent on dark matter's internal degree-of-freedoms, and under what circumstances, instabilities could lead to local gasless dark collapses. I will also show how dark-matter solitons are excited in cosmic walls and voids, how their interactions facilitate gas condensation, and how non-linear interactions generate positive- and negative-amplitude solitons of different scales. The astrophysical implications of these phenomena will be discussed.

Coffee and tea will be served 20 minutes prior to the seminar.