Black holes are regions of space where gravity is so intense that nothing, not even light, can escape their grasp. They come in dramatically different sizes. Stellar mass black holes are the remnants of massive stars that have collapsed under their own gravity, typically weighing between three and a few dozen times the mass of our Sun and compressed into a region just kilometres across. Supermassive black holes, by contrast, are the giants lurking at the centres of galaxies, weighing millions to billions of solar masses. These beasts didn’t form from a single collapsing star but grew over billions of years through gas accretion and mergers with other black holes.
This image from Hubble’s Wide Field and Planetary Camera 2 (WFPC2) is likely the best of ancient and brilliant quasar 3C 273, which resides in a giant elliptical galaxy in the constellation of Virgo (Credit : Hubble ESA)
Many of the supermassive black holes are the driving force behind quasars, some of the most luminous objects in the universe. An international team using the GRAVITY+ instrument at the Very Large Telescope Interferometer (VLTI) in Chile managed to gather information on a quasar 12 billion light years away and what they found challenges our understanding of them.
The breakthrough was made possible by the new adaptive optics system recently installed at the VLTI. Developed by the Max Planck Institute for Extraterrestrial Physics (MPE) and the GRAVITY+ consortium, the upgrade significantly improves the correction of atmospheric blurring resulting in images with unprecedented detail. It’s somewhat like giving the telescope a pair of glasses to correct for turbulence in our atmosphere in real time.
GRAVITY is a second generation instrument for the VLT Interferometer and allows the measurement of the positions and motions of astronomical objects on scales far smaller than is currently possible. The picture shows the instrument under test at the Paranal Observatory in July 2015 before its recent upgrade (Credit : MPE/GRAVITY team)
The team led by Ric Davies from the MPE, targeted an extreme object, a quasar so luminous it was only discovered by Australian astronomers in 2024. Using GRAVITY+, the team managed to resolve the quasar’s “broad line region,” the swirling zone of gas orbiting the supermassive black hole at the galaxy’s centre. This gave them a direct view of how material moves under the black hole’s immense gravitational pull. By combining these observations with spectroscopic data from ERIS (Enhanced Resolution Imager and Spectrograph on VLT), analysing both H-beta and H-gamma emission lines, they built a new model of the movement of gas in this region.
Despite the quasar’s extreme luminosity, the black hole at its heart weighs in at “only” 800 million solar masses, a factor of ten lower than previous estimates made using traditional methods. The new result is reliable precisely because it’s based on the actual motion of gas rather than statistical analysis alone. Many studies using the James Webb Space Telescope rely on the original methods of analysis but it’s now believed they likely break down at such an early epoch of the history of the universe. If this finding proves typical rather than exceptional, it means astronomers may have been significantly overestimating black hole masses in the young universe.
Understanding how supermassive black holes achieved their enormous masses so early in the evolution of the universe has been a central question, and if they were generally less massive than we thought, it changes the picture of their growth and evolution. The research team plans to follow up with observations of more quasars at similar distances to determine whether this discrepancy represents a broader trend or whether they’ve simply caught an unusual object.
Source : A look deep into the early universe: First infrared interferometry of a quasar at redshift 4