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A pulsar in a binary with a compact object in the mass gap between neutron stars and black holes

Published 18 Jan 2024 in astro-ph.HE, gr-qc, and nucl-th | (2401.09872v1)

Abstract: Among the compact objects observed in gravitational wave merger events a few have masses in the gap between the most massive neutron stars (NSs) and least massive black holes (BHs) known. Their nature and the formation of their merging binaries are not well understood. We report on pulsar timing observations using the Karoo Array Telescope (MeerKAT) of PSR J0514-4002E, an eccentric binary millisecond pulsar in the globular cluster NGC 1851 with a total binary mass of $3.887 \pm 0.004$ solar masses. The companion to the pulsar is a compact object and its mass (between $2.09$ and $2.71$ solar masses, 95% confidence interval) is in the mass gap, so it either is a very massive NS or a low-mass BH. We propose the companion was formed by a merger between two earlier NSs.

Citations (35)

Summary

  • The paper details the discovery of a binary pulsar system with a companion mass (2.09–2.71 solar masses) residing in the mass gap between neutron stars and black holes.
  • The methodology employs high-precision pulsar timing using MeerKAT and GBT data to analyze orbital dynamics, relativistic effects, and Shapiro delay observations.
  • The implications of the findings challenge traditional stellar evolution theories and refine gravitational wave models by offering insights into binary formation and merger scenarios.

Overview and Analysis of the PSR J0514-4002E Binary System Study

In their work, Ewan D. Barr and colleagues detail the observation and analysis of PSR J0514-4002E, a binary millisecond pulsar residing in globular cluster NGC 1851. This particular system is of significant astrophysical interest due to the estimated mass of the compact object companion, which falls into the so-called "mass gap." This gap is typically situated between the known masses of the heaviest neutron stars and the lightest black holes. This study offers vital insights into the characteristics, formation, and potential evolutionary history of such binary systems.

Summary of Observations and Methodology

Utilizing the Karoo Array Telescope (MeerKAT) and corroborated by archival data from the Green Bank Telescope (GBT), the authors have characterized the system with high precision. Their analysis covers the orbital dynamics, the spin parameters of the pulsar, and interaction effects captured through Shapiro delay observations. The orbital period of PSR J0514-4002E, which is approximately 7.44 days, and its eccentricity value of 0.71, make the binary system particularly dynamic and suitable for detailed computational analyses.

The study's methodologies involve complex pulsar timing techniques that consider both the relativistic and astrometric effects that can impact such measurements. A significant part of the analysis focuses on detecting and interpreting the periastron advance rate and constraining the potential contribution from relativistic effects to the timing model.

Implications of the Companion's Mass

Of notable interest is the companion's mass, estimated between 2.09 and 2.71 solar masses with 95% confidence, placing it directly within the mass gap. This positioning raises questions about whether the companion is a massive neutron star or a low-mass black hole. The absence of detectable radio emissions from the companion leads to inconclusive evidence regarding its exact nature.

The mass of the companion, alongside the characteristics derived from the binary system's interactions, proposes scenarios concerning its formation history. One such scenario is a past merger between two neutron stars, which would align with predicted mass ranges for such remnants post-merger.

Theoretical and Practical Implications

The implication of a mass gap object has considerable significance in the broader context of astrophysical phenomena. It challenges our current understanding of stellar evolution, neutron star physics, and black hole formation. From a theoretical perspective, it pushes the boundaries on the models predicting star collapse and binary merger outcomes. Practically, understanding such systems aids in refining gravitational wave predictions and interpreting signals observed from events in which neutron stars and black holes coalesce.

Additionally, the study leverages the combination of MeerKAT and GBT observations to refine the measurement of pulsar parameters. Such methodological advancements underscore the importance of exploiting diverse data sources to enhance the precision of astronomical measurements prominently affecting the field of radio astronomy.

Speculation on Future Developments

As instrumentation progresses, future observational campaigns can be expected to provide additional data, potentially confirming the companion's classification as either a neutron star or a black hole. Such analyses could be augmented by further gravitational wave detection efforts like those by LIGO/Virgo, especially if similar systems are identified.

In conclusion, this study exemplifies the intricate balance between observational data and theoretical modeling required in contemporary astrophysics. The positioning of PSR J0514-4002E's companion in the mass gap advances interdisciplinary discourse between observational discoveries and theoretical modeling to describe stellar and binary system evolution accurately.

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