Candidate tidal disruption event spotted in quasar 700 million years after Big Bang

Researchers say they may have caught a star being torn apart by a black hole in one of the earliest known quasars, offering a rare time-domain glimpse of how black holes were being fed about 700 million years after the Big Bang.

In a new arXiv preprint posted in late September, astronomer S. Fujimoto and colleagues report evidence for a tidal disruption event candidate in GNz7q, a previously known dust-reddened quasar in the GOODS-North field at redshift 7.1899, or 7.19. If that interpretation holds up, it would be the highest-redshift tidal disruption event candidate reported so far. The paper has not yet been peer reviewed. The team reconstructed the flare from more than two decades of imaging with Hubble, Spitzer and JWST.

GNz7q is not a newly found object. It was first reported in 2022 as a high-redshift dusty quasar candidate and has since been studied with JWST. Prior work cited in the new paper describes it as a compact, dusty starburst galaxy forming stars at about 330 times the sun’s mass each year and powered by a black hole of roughly 30 million solar masses.

What stands out in the new analysis is not simply that the source varied, but how it varied. After a rapid rise, the object faded smoothly by about 1.1 magnitudes in the rest-frame ultraviolet over roughly two years in its own rest frame, the authors report. The variability was also wavelength-dependent across 1 to 5 microns, a pattern they say is difficult to square with the ordinary flickering seen in active galactic nuclei, or AGN, the bright centers powered by feeding black holes.

According to the preprint, GNz7q sits above the 99.9th percentile of the Sloan Digital Sky Survey quasar variability distribution. The authors say they tested whether normal stochastic quasar variability could reproduce the multi-band light curve and found a probability of less than 10^-5. In the paper’s words, “We report a long-lived nuclear transient in GNz7q, a red quasar at z = 7.19.”

The team also argues against a superluminous supernova, saying the event lasts too long and radiates too much energy to match typical examples of those stellar explosions. Their preferred explanation is a thermal flare with a decline that follows t^-5/3, a decay law commonly associated with tidal disruption events, in which debris from a shredded star falls back toward the black hole and powers a bright flare.

Under that model, the event reached a peak bolometric luminosity of about 3 × 10^45 ergs per second and radiated a total of about 1.5 × 10^53 ergs. That would make it among the most energetic tidal disruption events known, the authors say. Using standard efficiency assumptions, they estimate the flare could have involved the disruption of a star of roughly a few solar masses, though that is model-dependent rather than a direct measurement.

The paper points to two additional clues from JWST. In NIRSpec observations taken in 2025 and 2026, the researchers report an extremely broad, redshifted Balmer-line component with a full width at half maximum of about 11,900 kilometers per second and a velocity offset of about positive 2,500 kilometers per second. They interpret that as consistent with a transient broad-line region produced by the flare, rather than the more settled gas motions usually seen around a quasar. JWST mid-infrared photometry, meanwhile, shows delayed emission that the team interprets as a dust echo — light from the flare absorbed and re-radiated by surrounding dust — with dust at about 1,485 kelvins and an effective radius of about 0.46 parsecs.

A tidal disruption event happens when a star passes close enough to a massive black hole to be torn apart by gravity. Most spectroscopically confirmed examples reported so far have been at much lower redshift, generally below about 1.2. That makes a candidate at 7.19 unusually important, because it would offer a rare look at black-hole fueling in the early universe. But for now, that interpretation remains a claim in a preprint, one likely to draw close scrutiny before it can be treated as settled.