Origin of anomalous orbital decay in XTE J1118+480

Determine the physical origin of the anomalously large orbital-period decay observed in the black-hole low-mass X-ray binary XTE J1118+480, including whether a dark-matter mini-spike can account for the discrepancy between the observed and standard-theory predictions.

Background

The paper discusses the measured orbital-period decay of the companion star in XTE J1118+480, which is approximately two orders of magnitude larger than the rate predicted by standard theory. Several explanations have been proposed, including mechanisms involving dark-matter mini-spikes around stellar-mass black holes, but the paper identifies the physical origin of the anomaly as unresolved. The authors subsequently investigate whether such mini-spikes could produce observable dark-matter annihilation signals, although their analysis does not resolve the orbital-decay problem itself.

References

However, the observed $\dot P$ is $\sim\mathcal{O}(102)$ larger than the standard theory prediction of $\dot P\simeq-0.02\,\rm ms\,yr{-1}$. While different solutions have been proposed for the anomaly, the mystery remain unsolved.

— Sub-TeV Singlino Dark Matter in light from Sagittarius A$^\ast$ and LUX-ZEPLIN Nuclear-Recoil Event  (2609.02994 - Chattopadhyay et al., 2 Sep 2026) in Introduction, paragraph discussing black-hole low-mass X-ray binaries