Month: October 2020

by Polychronis Koliogiannis

Neutron stars are the way for the Universe to manifest its densest objects with an internal structure. Their study requires the knowledge of the equation of state of the fluid in the interior of the star. While isolated neutron stars place constraints on the cold, catalysed matter, many dynamical phenomena depend sensitively on the equation of state of hot dense nuclear matter. The formation of proto-neutron stars, neutron stars mergers, as well as the aftermath remnant, depend on the equation of state at finite temperature, entropy per baryon, and a varying range of proton fraction. In this framework, we construct thermodynamically consistent equations of state to accurately describe thermal effects. Additionally, we study the thermal and rotation with the Kepler frequency effect on some of the most important quantities in neutron stars, including the mass and radius, the frequency, the Kerr parameter, the moment of inertia, etc. The extended study on these quantities and data from late observations of neutron stars, both isolated and in matter of merging, could provide useful insight and robust constraints on the equation of state of nuclear matter.

by Laura Sagunski

Longstanding anomalies in astrophysical observations on small scales suggest that dark matter might not be collisionless, as is commonly assumed, but could have sizable self-interactions. For the first time, we have probed the hypothesis of self-interacting dark matter (SIDM) at intermediate scales between galaxies and galaxy clusters. To model the SIDM halo density profiles, we have employed an observation-driven approach, the so-called Jeans model. So far, the limit on the self-interaction cross section from the Bullet Cluster is often cited as the strongest constraint on dark matter self-interactions. We show, however, that the halo density proles of relaxed systems like groups and clusters lead to much stronger bounds on the self-interaction cross section.

by Prof. Dr. Andreas Bauswein (Zoom Meeting ID:886 0167 6852   Password: 680019)

We describe generally the collapse behavior of neutron star mergers, which is quantitatively expressed by the threshold binary mass for prompt black formation. We discuss general dependencies of the threshold mass and sketch applications for instance for the equation of state constraints. Moreover, we describe the impact of the hadron-quark phase transition on the collapse behavior and postmerger gravitational wave emission.