  We present a physical model and spin-state analysis of the potentially
hazardous asteroid (23187) 2000 PN9. As part of a long-term campaign to make
direct detections of the YORP effect, we collected optical lightcurves of the
asteroid between 2006 and 2020. These observations were combined with planetary
radar data to develop a detailed shape model which was used to search for YORP
acceleration. We report that 2000 PN9 is a relatively large top-shaped body
with a sidereal rotation period of 2.53216$\pm$0.00015 h. Although we find no
evidence for rotational acceleration, YORP torques smaller than
$\sim$10$^{-8}$$\,\rm rad/day^{2}$ cannot be ruled out. It is likely that 2000
PN9 is a YORP-evolved object, and may be an example of YORP equilibrium or self
limitation.
