SDSS J120414.37+351800.5 quasar optical photometry

These "nitrogen-rich" (N-rich) quasars are a long-standing puzzle because their interstellar medium implies stellar populations with abnormally high metallicities. It has recently been proposed that N-rich quasars may result from tidal disruption events (TDEs) of stars by supermassive black holes.

The rapid enhancement of nitrogen and the depletion of carbon due to the carbon-nitrogen-oxygen cycle in supersolar mass stars could naturally produce high N/C. However, the TDE hypothesis predicts that the N/C should change with time, which has never hitherto been observed. Here we report the discovery of the first N-rich quasar with rapid N/C variability that could be caused by a TDE. Two spectra separated by 1.7yrs (rest-frame) show that the NIII]{lambda}1750/CIII]{lambda}1909 intensity ratio decayed by ~86%+/-14% (1{sigma}).