A look deep into the early universe: First infrared interferometry of a quasar at redshift 4

New GRAVITY+ and ERIS observations uncover surprising black hole properties and powerful gas outflows in the early cosmos.

Using cutting-edge technology on the Very Large Telescope in Chile, the GRAVITY+ team managed to peer deep into the most luminous quasar known: a galaxy more than 12 billion light-years away. The astronomers were able to resolve its inner structure and more accurately determine the mass of its central black hole, which is much less than expected with the usual relations. In addition, they also found a prominent outflow, rather than most of gas rotating around the black hole. This shows that astronomers can now use GRAVITY+ to study active galaxies in the same epochs as JWST.

This pioneering observation, the first of its kind at such a high redshift, was made possible by the new Adaptive Optics (AO) systems recently installed at the Very Large Telescope Interferometer (VLTI). Developed by the Max Planck Institute for Extraterrestrial Physics (MPE) and the GRAVITY+ consortium, the AO upgrade significantly improves the correction of atmospheric blurring – adapting technology previously implemented in the ERIS instrument – to allow for deeper, more sensitive observations of the distant Universe.

The target of the observation is the most luminous known quasar (QSO) at redshift 4 – more than 12 billion light-years away and well before the era known as “cosmic noon.” The quasar studied here is an extreme object whose discovery was only reported by a team of Australian astronomers in 2024. Using the GRAVITY+ instrument, the team now resolved its “broad line region” (BLR) – the area of gas swirling around the supermassive black hole at the galaxy’s center – giving them a direct view into how material is moving under the black hole’s gravitational pull. Combining these data with a spectrum from the ERIS instrument, the team simultaneously analyzed the H-beta and H-gamma emission lines, yielding a robust and detailed kinematic model of the gas dynamics in this region.

A Lighter-than-Expected Black Hole

Despite the quasar’s extreme luminosity, the black hole at its heart was found to have a mass of “only” 800 million solar masses – a factor of ten lower than estimates made using traditional scaling relations.

“Our result is reliable because it’s based on the actual motion of the gas,” says Ric Davies, the lead scientist at MPE. “Many JWST studies make use of scaling laws that might not hold at these early times. If our findings are typical, it means black hole masses in the early Universe may have been systematically overestimated.”

The team plans to follow up with observations of more quasars at similar redshifts to determine whether this discrepancy is a broader trend.

A Powerful Outflow

In a second surprising result, the team found that 80% of the gas in the BLR is not rotating around the central black hole, but is being blown outwards at speeds of up to 10,000 km/s.  “This is the most prominent outflow we’ve seen, and rather than studying the gas on larger scales after it has interacted with the gas in the host galaxy, these data have enabled us to resolve its launching site,” explains Taro Shimizu, who led the observations and participated in the analysis. These outflows are thought to play a crucial role in regulating galaxy growth and black hole accretion, so resolving them at their launching point is a major step forward in understanding galaxy evolution.

These results were achieved in collaboration with the new Max Planck Partner Group in Beijing led by Jinyi Shangguan, and they demonstrate that infrared interferometry can now reach into the same epoch as JWST, offering complementary insights with far higher spatial resolution.