Millisecond Pulsars and Black Holes in Globular Clusters

Abstract

Over a hundred millisecond radio pulsars (MSPs) have been observed in globular clusters (GCs), motivating theoretical studies of the formation and evolution of these sources through stellar evolution coupled to stellar dynamics. Here we study MSPs in GCs using realistic $N$-body simulations with our Cluster Monte Carlo code. We show that neutron stars (NSs) formed in electron-capture supernovae (including both accretion-induced and merger-induced collapse of white dwarfs) can be spun up through mass transfer to form MSPs. Both NS formation and spin-up through accretion are greatly enhanced through dynamical interaction processes. We find that our models for average GCs at the present day with masses $\approx 2\times 10^5{M}_{\odot }$ can produce up to $10-20$ MSPs, while a very massive GC model with mass $\approx 10^6{M}_{\odot }$ can produce close to $100$. We show that the number of MSPs is anti-correlated with the total number of stellar-mass black holes (BHs) retained in the host cluster. The radial distributions are also affected: MSPs are more concentrated towards the center in a host cluster with a smaller number of retained BHs. As a result, the number of MSPs in a GC could be used to place constraints on its BH population. Some intrinsic properties of MSP systems in our models (such as the magnetic fields and spin periods) are in good overall agreement with observations, while others (such as the distribution of binary companion types) less so, and we discuss the possible reasons for such discrepancies. Interestingly, our models also demonstrate the possibility of dynamically forming NS--NS and NS--BH binaries in GCs, although the predicted numbers are very small.

14 pages, 6 figures, Accepted for publication in ApJ

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• Discovery of the optical afterglow and host galaxy of short GRB181123B at $z=1.754$: Implications for Delay Time Distributions
• Demographics of neutron stars in young massive and open clusters
• Globular cluster formation histories, masses and radii inferred from gravitational waves
• Impact of natal kicks on merger rates and spin-orbit misalignments of black hole -- neutron star mergers
• Demographics of triple systems in dense star clusters
• Evidence of non-luminous matter in the center of M62
• Missing for 20 years: MeerKAT re-detects the elusive binary pulsar M30B
• Radio detection of an elusive millisecond pulsar in the Globular Cluster NGC 6397
• Coherent Search for Binary Pulsars across all Five Keplerian Parameters in Radio Observations using the template-bank algorithm
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• 4FGL J1120.0-2204: A Unique Gamma-ray Bright Neutron Star Binary with an Extremely Low Mass Proto-White Dwarf
• Timing of Pulsars in the Globular Cluster Omega Centauri
• Millisecond Pulsars in Dense Star Clusters: Evolution, Scaling Relations, and the Galactic-Center Gamma-ray Excess
• Wideband Monitoring Observations of PSR J1803-3002A in the Globular Cluster NGC 6522
• How the dynamical properties of globular clusters impact their $\gamma$-ray and X-ray emission
• Influences of dynamical disruptions on the evolution of pulsars in globular clusters
• Reevaluating the Origin of Detectable Cataclysmic Variables in Globular Clusters: Testing the Importance of Dynamics