Ringdown at the Bottom of the Band: The Fundamental Mode of the GW190521 Remnant and Its Measurable Cycles

GW190521 produced the heaviest remnant in the second catalogue, about one hundred and forty-two solar masses, and heaviness moves the ringdown downward in frequency toward the seismic wall of the instruments. This paper computes where the fundamental mode of that remnant actually sits, how many cycles of it the detectors can plausibly follow before it decays, and how the measurable information content compares with a mid-mass event of similar intrinsic loudness. For the 142 solar mass remnant (258 solar masses in the detector frame at its published distance) with spin 0.72, the dimensionless frequency is 0.5437 and the quality factor is 3.378. The physical ringdown frequency is 68.0 Hz, only 0.273 of the 249.1 Hz computed for a sixty-two solar mass remnant at the same machinery, and the period of one oscillation is 14.71 ms. The damping time is 15.82 ms, so the mode completes 1.08 cycles per e-folding and stays above one tenth of its starting amplitude for 36.4 ms. The mode sits at 68.0 Hz with 1.08 cycles per e-folding, roughly 0.27 of the frequency of a mid-mass remnant, which quantifies why heavy remnants are detected loudly but measured poorly in their ringdown. This study is computed from stated assumptions and published catalogue values; it is simulated, not measured.