Abstract
In this paper, the merger rate of black holes in a cluster of primordial black holes (PBHs) is investigated. The clusters have characteristics close to those of typical globular star clusters. A cluster that has a wide mass spectrum ranging from 10−2 to 10M⊙ (Solar mass) and contains a massive central black hole of the mass M•=103M⊙ is considered. It is shown that in the process of the evolution of cluster, the merger rate changed significantly, and by now, the PBH clusters have passed the stage of active merging of the black holes inside them.
Highlights
In the calculations described in this paper, it is shown that during cluster evolution, mergers mainly occur with a central black hole; the merger rate is low
It is known that a physically valid density profile in the presence of a central black hole (CBH) must be steeper than r −1/2 [34]
The results do not depend on the profile shape because the expansion phase starts very quickly after ∼ 100 Myr [8,9], the time when the core collapse occurs in the model without a CBH for this cluster
Summary
The second type describes cluster formation via gravitational collapse of domain walls appearing in the early Universe as a result of the evolution of scalar fields in the inflationary epoch; see review [7] and references therein. The considered PBHs clusters might have black holes with a wide range of masses and a massive black hole at the center. This paper continues the previous investigation and explores the merger rate of black holes during the evolution of such clusters. In the calculations described in this paper, it is shown that during cluster evolution, mergers mainly occur with a central black hole; the merger rate is low
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