A new study has cast doubt on the accuracy of the first-ever image of Sagittarius A*, the supermassive black hole at the center of the Milky Way, which was captured by the Event Horizon Telescope (EHT) in 2022.
This iconic “glowing doughnut” image, celebrated for offering humanity’s first glimpse of our galaxy’s central black hole, may not fully reflect Sagittarius A*’s true structure, according to researchers from Japan’s National Astronomical Observatory. Their findings suggest that certain imaging processes might have obscured important details, prompting a re-evaluation of this breakthrough image.
Re-examining Sagittarius A*’s True Shape
The research team, led by Assistant Professor Miyoshi Makoto, revisited the original EHT data using alternative analysis methods. Their findings revealed that Sagittarius A*’s accretion disk—the rotating disk of gas surrounding the black hole—might not be as circular as the image suggests. Instead, the disk appears to be “slightly elongated in the east-west direction,” with the eastern side brighter than the west. Makoto explained that this uneven brightness might be due to relativistic beaming, where light moving toward Earth appears intensified, while light moving away appears dimmer, creating an illusion of asymmetry.
These findings challenge the traditional “ring” interpretation and propose that the EHT image may have smoothed out details due to imaging artifacts. Because black holes are surrounded by highly dynamic environments with swirling gases moving at nearly the speed of light, capturing an accurate image is especially challenging, with data interpolation potentially altering the image’s representation.
The Complexities of Imaging a Black Hole
Imaging Sagittarius A* required a global network of telescopes that together formed a “virtual” Earth-sized telescope, collecting vast data sets through a process known as very long baseline interferometry (VLBI). This method combines signals from telescopes across continents to generate an image with unprecedented resolution, but it involves data interpolation, which can introduce artifacts. In the case of Sagittarius A*, the study suggests that this interpolation may have imposed a symmetrical ring shape on an otherwise asymmetric structure.
Makoto noted that “no telescope can capture an astronomical image perfectly,” stressing that while VLBI provides immense detail, it is also susceptible to assumptions that might oversimplify complex features in the final image. These challenges are compounded by Sagittarius A*’s rapidly spinning accretion disk, which rotates close to 60% of the speed of light. As a result, the turbulent environment around Sagittarius A* adds to the difficulty of capturing a precise image, particularly if rapid changes are not accounted for in the image processing.
Implications for Future Imaging of Black Holes
The study’s findings highlight the need for refined imaging techniques to capture accurate representations of black holes, especially with the complex and dynamic environment surrounding Sagittarius A*. Future observations from the EHT, potentially incorporating upgraded instruments and new data processing methods, could provide a more accurate look at Sagittarius A*. These advancements will also be crucial as the EHT prepares to observe other supermassive black holes in our galaxy and beyond.
As black hole imaging technology continues to evolve, scientists hope that revised imaging techniques will enable them to capture more detailed views of supermassive black holes and their accretion disks, enhancing our understanding of these elusive cosmic objects. The study underscores the importance of re-examining foundational data in light of new methodologies to ensure that scientific breakthroughs offer the most accurate insights possible.