Circumbinary disks in post common envelope binary systems with compact objects

TL;DR

This study uses population synthesis modeling to investigate the formation of circumbinary disks after common envelope evolution in massive binary systems, revealing their impact on binary evolution and gravitational wave event rates.

Contribution

It introduces a parameterized model for CBD formation post-CEE and analyzes its effects on the evolution and merger rates of double compact object binaries.

Findings

CBD formation is most common in BH-BH and NS-NS binaries expected to merge within Hubble time.

Interaction with CBD can reduce DCO merger rates, affecting gravitational wave predictions.

CBD interactions may lead to luminous transients instead of gravitational wave sources.

Abstract

We conduct a population synthesis study using the binary population synthesis code compas to explore the formation of circumbinary disks (CBDs) following the common envelope evolution (CEE) phase of a giant star and a neutron star (NS) or black hole (BH). We focus on massive binary systems that evolve into double compact object (DCO) binaries after the exposed core of the giant collapses to form a second NS or BH. A CBD around the binary system of the giant's core and the compact object alters the orbital evolution of the binary. We parameterize the conditions for CBD formation in post-CEE binaries and present characteristics of DCO progenitors that are likely or unlikely to form CBDs. We find that CBD formation is most common in BH-BH binaries and NS-NS binaries that are expected to merge within Hubble time. Furthermore, we find that the interaction of the CBD with the core - NS/BH system at the termination of the CEE reduces the expected rate of DCO mergers, regardless of whether these binaries tighten or expand due to this interaction. If the binary system loses angular momentum to the CBD, it may produce a luminous transient due to a merger between the NS/BH and the core of the giant rather than gravitational wave sources. Thus, accounting for post-CEE CBD formation and its interaction with the binary system in population synthesis studies is significant for obtaining reliable predictions of the gravitational wave event rates expected by current detectors.