arXiv subjects

Lotem Unger

Publications and source records attributed to Lotem Unger.

2 recordsLinked to original sources

arXiv2026

Stellar black hole binaries from two common envelope evolution phases in triple stellar systems

We propose a triple-star evolutionary channel involving two common envelope evolution (CEE) phases to form close binary black hole (BBH) systems with an average positive effective inspiral spin $\chi_{\rm eff}$ and a tail of systems having $\chi_{\rm eff}<0$, as observed by gravitational wave detectors. $\chi_{\rm eff}$ is the mass-weighted spin of the two merging BHs, and a positive (negative) value indicates an effective spin along (opposite) the orbital angular momentum. The first BH progenitor engulfs a low-mass star during the post-main-sequence evolution. The tertiary star spirals in and spins up the core, which forms the first BH at the first core-collapse supernova (CCSN) explosion. Its spin is along the orbital angular momentum of the inner binary, which can be highly inclined to the outer binary angular momentum. The secondary star later engulfs the BH in a second CEE phase and explodes as a CCSN to form the second BH with a spin that is more aligned with the orbital angular momentum of the two BHs. We use empirically calibrated initial distributions of triple-star systems consisting of two massive stars and impose a hierarchical stability criterion. We compare the predicted ratio of merging BBHs to CCSN explosion rates and find it is up to a factor of 2 larger than the observed rate. This channel can significantly contribute to the population of observed merging BBHs and can explain their qualitative spin distribution.

astro-ph.HE↗

arXiv2024

Circumbinary disks in post common envelope binary systems with compact objects

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.

astro-ph.SR↗