A tidal disruption event in a quasar at redshift 7.19

The study reports a long-lived nuclear transient in GNz7q, a red quasar at z=7.19 powered by a black hole of roughly 3×10^7 solar masses and hosted by a compact, dusty starburst galaxy. The transient was identified using more than two decades of imaging from HST, Spitzer, and JWST, providing a rare time-domain view of a high-redshift quasar system.

After a rapid rise, the source faded smoothly by Δm ≈ 1.1 mag in the rest-frame ultraviolet over about 2 rest-frame years. Its coherent, wavelength-dependent evolution across 1–5 μm places GNz7q above the 99.9th percentile of the SDSS quasar variability distribution and is not seen at z ≳ 5. The duration and energetics disfavor superluminous supernovae, while stochastic quasar variability can reproduce the multi-band evolution with probability ≲10^-5.

A panchromatic model combining a thermal continuum with a t^-5/3 decline reproduces the light curves. It yields a peak bolometric luminosity of approximately 3×10^45 erg/s and a radiated energy of approximately 1.5×10^53 erg, implying the tidal disruption of a star of a few solar masses and placing the event among the most energetic TDEs known.

Independent JWST/NIRSpec spectroscopy shows a redshifted, extremely broad Balmer-line component consistent with a transient, non-virialized broad-line region. JWST/MIRI photometry additionally reveals delayed mid-infrared emission from ~1500 K dust at a sub-parsec radius, consistent with a dust echo of the flare. The relatively low black-hole mass and dense star-forming nucleus of GNz7q are conditions under which TDEs are expected to be most efficient.

These observations provide a time-domain view of episodic black-hole fueling and its dusty nuclear environment 700 million years after the Big Bang. Wide-field near-infrared surveys with Roman and Euclid, complemented by LSST at lower redshifts, may uncover such transients in large numbers.