When astronomers first unveiled the image of Sagittarius A*, the supermassive black hole at the center of the Milky Way, it was hailed as a stunning triumph. It was a portrait of the ultimate darkness itself. Suspended in the image was a black void encircled by a glowing, doughnut-like ring of light, the product of superheated gas spiraling toward an inevitable descent into the black hole.
For a moment, it seemed as if we were staring straight into the eye of the heart of our galaxy. But now, a new study suggests this may have been an illusion all along — or at least, not entirely accurate.
Sagittarius A* from a new perspective
In a surprising turn, researchers from Japan’s National Astronomical Observatory (NAOJ) are arguing that Sagittarius A* may not look like the symmetrical “doughnut” depicted in 2022. Instead, they believe it’s more likely an elongated oval, glowing brighter on one side than the other. The team, led by astronomer Miyoshi Makoto, argues that the imaging techniques used by the Event Horizon Telescope (EHT) to construct the original picture may have inadvertently included some processing errors, creating a ring-like shape where none exists.
Makoto’s team combed through the same 2017 data that the EHT scientists used to build their version of Sagittarius A*. But instead of relying on the EHT’s specialized imaging software, they applied more traditional imaging methods, unveiling a structure that’s slightly longer than it is wide. The eastern side shines brighter than the western half, they say, likely because the black hole’s accretion disk is rotating at incredible speed, close to 60 percent the speed of light.
“Our image is slightly elongated in the east-west direction, and the eastern half is brighter than the western half,” Makoto said in a press statement.
He added: “Why, then, did the ring-like image emerge? Well, no telescope can capture an astronomical image perfectly. We hypothesize that the ring image resulted from errors during EHT’s imaging analysis and that part of it was an artifact, rather than the actual astronomical structure.”
A Cosmic Rorschach Test
Miyoshi et al.
This controversy adds a new chapter to the brief but intense history of black hole imaging. When the EHT collaboration released its first-ever image of a black hole in 2019, showing the giant at the core of the galaxy Messier 87, it felt like a momentous revelation. For decades, black holes had been confined to theory and mathematics. Astronomers knew they were real through indirect means that underscored the black holes’ immense gravitational pull.
But then, here it was: a black shadow surrounded by the glowing embers of a cosmic pyre. And when the team followed up with a 2022 image of Sagittarius A*, the black hole at the center of our own galaxy, it seemed like the universe was giving up one of its darkest secrets.
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However, imaging a black hole is anything but simple. Black holes cannot be seen directly; light does not escape them. Instead, astronomers look for the telltale ring of light created by an “accretion disk”. These are essentially whirlpools of superheated matter spiraling toward the black hole, emitting energy in the form of light before it crosses into the point of no return. The EHT created an image of this fiery outline using data from a network of eight telescopes around the world, gathering information across a vast range of Earth’s surface. But even with all those telescopes, there were still gaps in the data, which the EHT team filled using an algorithm that stitched the fragments together.
It’s this stitching, Makoto’s team argues, that may have smoothed out the true shape of the disk, giving it a rounded “doughnut” form instead of the more irregular shape they believe actually exists. Using a simpler imaging method, they suggest, leads to a truer shape — a brightening on one side, a slight stretch along the edges, and a subtle asymmetry. It’s a cosmic Rorschach test, and the answer depends on which algorithm is used. Perhaps even this new interpretation is not entirely accurate — but we’re getting there, it seems.
The Future of Black Hole Portraiture
This debate isn’t just about image quality. It’s about getting closer to understanding the forces that shape black holes, and by extension, the universe itself. Black holes are the endgame of gravity. These are places where matter is torn apart into its smallest subatomic components and eventually squeezed into the singularity. Black holes wield an influence so profound they alter the very fabric of space and time around them. An accurate image of Sagittarius A* would help astronomers better understand this unseen giant, lurking at the core of our galaxy, swallowing anything that comes too close.
The timing of Makoto’s findings is fortuitous. Since the release of the EHT’s 2022 image, technology has only improved. This August, the EHT team released a new imaging technique that sharpens the telescope’s resolution, making it possible to capture even clearer and more detailed images of cosmic phenomena. There are even discussions about a $300 million “Event Horizon Explorer,” a space-based telescope that could one day give us a crystal-clear look at black holes’ so-called “photon rings” — the last ring of light that narrowly escapes a black hole’s gravitational pull.
If anything, this debate shows that the universe is not so easily revealed. But as algorithms evolve and new tools come online, we may find that the black hole at the center of the Milky Way has far more to tell us than we ever imagined.
The new findings by Makoto et al were published in the Monthly Notices of the Royal Astronomical Society.