New measurements by GRAVITY+ challenge long-held estimates of the Universe’s brightest quasar
Peering back to the early universe often requires scientists to rely on indirect methods and assumptions. A recent study, however, leveraged the GRAVITY+ instrument on the European Southern Observatory’s Very Large Telescope Interferometer (ESO VLT) to map the Broad Line Region (BLR) of J0529, the brightest known quasar. The result is a mass estimate dramatically smaller than prior calculations—about one-tenth of the original figure.
How did researchers measure a black hole’s mass in a distant quasar?
Traditionally, astronomers estimate a black hole’s mass by inferring the velocity of gas orbiting the black hole from the width of emission lines in the quasar’s spectrum. Faster orbital speeds imply a more massive central object, with mass proportional to the square of the velocity and to a characteristic radius. In the case of J0529, discovered in 2024 and located roughly 12.5 billion light-years away (when the universe was about 1.5 billion years old), the initial method yielded a colossal estimate: around 10 billion solar masses.
The breakthrough with GRAVITY+ and what changed
GRAVITY+ combines light from all four 8-meter VLT telescopes into a single, more powerful “virtual” telescope. This interferometric capability enables astronomers to resolve the BLR—the clouds of gas orbiting the black hole—with unprecedented clarity. In the J0529 observations, scientists could actually observe a high-velocity gas outflow, a jet-like stream moving at about 10,000 km/s, emanating from the quasar’s core.
The key insight: those fast-moving gases were not all in bound, circular orbits around the black hole. A significant portion of the broad emission line width was produced by these outflows, not by the gravitationally bound motion used in the classic mass calculation. If one misattributes the line broadening to orbital speed alone, the inferred mass can be substantially overestimated.
Revised mass and its implications
By spatially isolating and subtracting the contribution of the outflows from the spectral data, the team recalculated J0529’s mass. The updated figure is about 800 million solar masses—roughly 10% of the prior estimate. While still enormous, this revised mass reshapes our understanding of how such behemoths formed so early in cosmic history and challenges models that demanded even more rapid growth to reach the observed sizes.
Why this matters for black hole growth theories
The J0529 findings touch on the broader debate about supermassive black holes in the early universe. The presence of bright quasars at these early times has prompted questions about efficient growth mechanisms. The revised mass supports growth scenarios that may involve more moderate, sustained accretion, or episodic, “super-Eddington” phases that briefly exceed theoretical luminosity limits yet do not necessarily translate into perpetual, runaway mass increases.
Super-Eddington accretion and its role in jet formation
Observations suggest J0529’s powerful outflows are linked to a process called super-Eddington accretion, where a black hole accretes gas at rates that temporarily eclipse the Eddington limit. While such accretion can boost luminosity, it can also drive material away via powerful jets, potentially regulating the black hole’s long-term mass growth and impacting its host galaxy’s star formation.
Looking ahead: better instruments, better answers
As astronomical instruments grow more capable, we can expect further refinements to black hole mass measurements in the distant universe. The new results for J0529 underscore the importance of directly observing the BLR and accounting for non-orbital gas dynamics when interpreting spectral lines. This ongoing cycle—where improved technology both questions old assumptions and invites new theories—drives progress in our understanding of the cosmos.
