The first photo of our galaxy's black hole isn't one photo—it's thousands of images averaged together, because Sgr A* changes minute to minute.
The 2022 image of Sagittarius A* is not a single snapshot but the average of thousands of separately reconstructed images, each one a valid fit to data the Event Horizon Telescope collected in April 2017.
When the Event Horizon Telescope released the first picture of the black hole at the center of our galaxy on May 12, 2022, it looked like a photograph: a bright orange ring around a dark center. But it isn't a photograph in any ordinary sense. As Caltech explained in its announcement that day, the main image "was produced by averaging together thousands of images created using different computational methods—all of which accurately fit the EHT data." What you are looking at is a composite—a consensus drawn from thousands of separate reconstructions of the same night's observations.
The reason comes down to speed. The EHT gathered its Sagittarius A*, or Sgr A*, data across several nights in April 2017, with the team focusing its analysis on the observations of April 7. But Sgr A* is a small black hole by cosmic standards, roughly four million times the mass of the Sun, and gas orbiting close to it whips around in minutes. In the collaboration's own words, published in *The Astrophysical Journal Letters* (paper IV, ApJL 930, L15), the source violates the "static-source assumption" that ordinary imaging relies on—it changes on timescales as short as minutes over the course of an observing night.
Why one snapshot wouldn't work
Standard radio imaging assumes the thing you're photographing holds still while you collect a full night of data. That assumption held for M87*, the first black hole the EHT imaged in 2019. M87* is a monster—thousands of times more massive than Sgr A*—and its gas orbits so slowly that it stayed essentially frozen across an entire night. Sgr A* does the opposite.
Katie Bouman, one of the EHT imaging leads at Caltech, put the scale of the problem plainly to *Quanta Magazine*: the material swirling around Sgr A* moved so fast that the black hole's appearance could change from minute to minute, with activity running about a thousand times faster than on M87*. As AAS Nova noted in its summary of the results, the brightness of Sgr A* varied within a single day—forcing the team to develop new algorithms built to tolerate that rapid variation rather than assume it away.
How the average was built
Faced with a target that refuses to sit still, the collaboration didn't try to freeze a single instant. Instead, it ran the 2017 data through several independent imaging pipelines, each using different computational assumptions and each generating many candidate images. Every one of those thousands of reconstructions had to be consistent with what the telescopes actually recorded. The published ring is the average of that ensemble, sorted into representative clusters and blended so that no single method's quirks dominate the final picture.
It is worth being precise about what was averaged. These were reconstructed images fitting the real observations—not the separate library of GRMHD computer simulations the team used elsewhere to test physical models of the accretion flow and estimate the black hole's mass. The picture is a distillation of the measurements, not a rendering of a model.
The vivid part is that the "true" appearance of Sgr A* on the night of April 7, 2017, may have flickered through dozens of configurations while the telescopes stared. The ring you see is closer to a long-exposure portrait of a fidgeting subject than a crisp instant.
And that is the seam still open to argument. Averaging tames the variability, but it also blurs it—any given moment that night might have looked meaningfully different from the smooth ring the world now recognizes. How much real structure the averaging washes out, and whether faster instruments or movie-making techniques could someday resolve Sgr A* changing in real time, remains an active question. The 2022 image is a stunning first look, but it is a first look at a black hole that never once held its pose.