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.
Conclusion:
Based on pulsar timing observations using the Karoo Array Telescope (MeerKAT), PSR J0514-4002E, an eccentric binary millisecond pulsar in the globular cluster NGC 1851, has a companion with a mass in the gap between neutron stars and black holes. The mass of the companion is estimated to be between 2.09 and 2.71 solar masses, suggesting it could be either a very massive neutron star or a low-mass black hole. The formation of this merging binary and the nature of the companion are not well understood.
Roadmap:
Challenges:
- Understanding the nature of the companion: The mass of the companion falls within the mass gap, which poses challenges in determining whether it is a neutron star or a black hole. Further research and theoretical modeling are required to better understand its properties and characteristics.
- Formation of merging binaries: The formation of merging binaries, especially those with objects in the mass gap, is not well understood. Exploring the mechanisms and processes involved in the formation of these binaries will be crucial in unraveling the mysteries surrounding compact objects.
Opportunities:
- Advancement in pulsar timing observations: Continued advancements in telescopes and observational techniques, such as MeerKAT, provide opportunities to study and analyze more binary millisecond pulsars. By observing similar systems, researchers can gather more data to refine their understanding of compact objects and their formation.
- Theoretical modeling and simulations: The discovery of PSR J0514-4002E and its companion opens up opportunities for theoretical physicists and astrophysicists to develop models and simulations that can explain the formation and evolution of compact objects in the universe. These models can help test various hypotheses and provide insights into the nature of these enigmatic objects.