Gravitational waves from equatorially eccentric extreme mass ratio inspirals around swirling Kerr black holes

Abstract: We have studied the gravitational wave generated by extreme mass ratio inspirals (EMRIs) along eccentric orbits on equatorial plane within the frame of the swirling-Kerr black hole spacetime. The swirling-Kerr black hole has an extra swirling parameter, which characterizes the rotation of universe background. Our findings indicate that this swirling parameter leads to a delay phase shift in the gravitational waveforms. The impact of the swirling parameter on EMRI gravitational waves is suppressed by the black hole's spin parameter. As a result, extracting information about the swirling parameter from gravitational waves in a static black hole spacetime is much easier than in the case of a rapidly rotating black hole. Our analysis also shows that a high black hole spin leads to a greater overlap of gravitational waveforms for different swirling parameters. We further investigate the potential issue of waveform confusion caused by the orbital eccentricity and semi-latus rectum parameters. As the swirling parameter increases, the relative variation in eccentricity also increases, while the variation in the semi-latus rectum decreases rapidly. The trends in these changes with the swirling parameter resemble those observed with the MOG (Modified Gravity) parameter, though with different rates of change. These results provide deeper insights into the properties of EMRI gravitational waves and the swirling of the universe background.