Granular mass perturbations on the pulsar - supermassive black hole system
Abstract
Discovery and timing observations of a radio pulsar orbiting around Sagittarius A*, the supermassive black hole (SMBH) in our Galactic Centre (GC), will provide unprecedented opportunities of studying the SMBH spacetime, testing gravity theories, and probing the astrophysical environment in the GC. However, unknown mass distributions might cause timing residuals that are much larger than the timing precision. With extensive numerical simulations, for the first time we find that the perturbations caused by a granular cusp of stellar-mass black holes in the GC lead to post-fit timing residuals of 10-100 s--contrary to traditional wisdom--even for a pulsar in a tight orbit with an orbital period Pb=0.5 yr. Such a large timing residual can lead to significant measurement bias or even prevent construction of a phase-connected timing solution for the full orbit. We revisit the idea of extracting SMBH parameters only with data around periastron where the perturbation is small. Under the realistic phase-disconnected assumption, we point out that it is vital to consider the frame-dragging effect in the light propagation, which breaks parameter degeneracy and leads to an order of magnitude improvement for the measurement precision of the SMBH spin.
Versions
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BibTeX
@misc{hu2026granular,
title = {{Granular mass perturbations on the pulsar - supermassive black hole system}},
author = {Zexin Hu and Lijing Shao},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.04762},
eprint = {2606.04762},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.04762},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Granular mass perturbations on the pulsar - supermassive black hole system
AU - Zexin Hu
AU - Lijing Shao
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2606.04762
UR - https://arxiv.org/abs/2606.04762
AB - Discovery and timing observations of a radio pulsar orbiting around Sagittarius A*, the supermassive black hole (SMBH) in our Galactic Centre (GC), will provide unprecedented opportunities of studying the SMBH spacetime, testing gravity theories, and probing the astrophysical environment in the GC. However, unknown mass distributions might cause timing residuals that are much larger than the timing precision. With extensive numerical simulations, for the first time we find that the perturbations caused by a granular cusp of stellar-mass black holes in the GC lead to post-fit timing residuals of 10-100 s--contrary to traditional wisdom--even for a pulsar in a tight orbit with an orbital period P_b=0.5 yr. Such a large timing residual can lead to significant measurement bias or even prevent construction of a phase-connected timing solution for the full orbit. We revisit the idea of extracting SMBH parameters only with data around periastron where the perturbation is small. Under the realistic phase-disconnected assumption, we point out that it is vital to consider the frame-dragging effect in the light propagation, which breaks parameter degeneracy and leads to an order of magnitude improvement for the measurement precision of the SMBH spin.
ER -