The Event Horizon Telescope’s “Image” of Sagittarius A*

In my novel Infernum, the crew of the Avenger are handed a one-way mission to the center of our galaxy. While we don’t have the technology to make such a trip today, we’ve taken a stab at gazing into the supermassive black hole, dubbed Sagittarius A* (Sgr A*), that lives there. The Event Horizon Telescope’s “image” of Sgr A* was hailed as a monumental achievement in astrophysics. But was it truly an image in the traditional sense? Many assume it’s an actual photograph of the black hole. The process of transforming radio wave data into a visual representation is far from straightforward. Recent re-analyses by Japanese scientists have added further skepticism, reinforcing that what we see may be as much interpretation as observation.

Here’s a breakdown of how the Event Horizon Telescope (EHT)’s so-called “image” was generated and why it’s not as straightforward as it seems.

Unlike a conventional camera, which captures light in the visible spectrum, the EHT gathers data in the form of radio waves. These waves hold essential frequency and amplitude values, but they don’t create a picture directly. Each of the EHT’s telescopes captures these radio signals as they arrive from Sgr A*, recording slight differences in arrival times to calculate the phase and amplitude of the waves. This information encodes how different parts of the black hole region emit radio waves at varying intensities.

But at this stage, we’re still not dealing with an “image.” What we have is a complex dataset, rich in spatial frequency information, but lacking the spatial structure we typically associate with a picture.

To move from frequency data to spatial information, the EHT team uses a Fourier Transform. This mathematical operation translates the collected frequency information into a “brightness map,” which reveals where radio waves are emitted most intensely within the region surrounding Sgr A*.

The process is similar to creating a heat map, where radio wave intensity maps to brightness. However, what we end up with isn’t an accurate portrayal of the black hole’s appearance; it’s a mathematical model of brightness variations within the region.

Even after the Fourier Transform, there are substantial gaps in the data. The Event Horizon telescopes can only cover so much of the sky, meaning that parts of the “image” remain uncertain or incomplete. The EHT team addresses this with interpolation, a statistical method to estimate missing data points based on the information they do have. They also apply regularization techniques to make the final image conform to what we expect a black hole’s surroundings to look like. For instance, maximum entropy regularization keeps the image smooth and free of unrealistic artifacts.

These processes, while grounded in statistical rigor, are inherently interpretive. They also rely on assumptions about the physical properties of black holes and the areas surrounding them, taking on faith that we have a full understanding of how they behave.

Once we have a refined brightness map, it’s still just that—a map of intensity without any color. To make it more accessible, the EHT team applies a color gradient to the grayscale map. This palette, typically a fiery yellow-orange-red gradient, does not represent real colors of the black hole. Instead, it uses color to highlight areas with higher radio wave intensity, which helps human observers interpret the image.

So, the final “picture” is not a true image, but rather a false-color composite. It’s visually compelling, but entirely symbolic in its color choices.

The end result that we see—the image released by the EHT—is a layered construct:

• The radio wave intensity data produces a brightness map.

• Statistical interpolation and regularization fill in data gaps, ensuring the image is smooth.

• A false-color gradient adds a visually intuitive, though arbitrary, color scheme.

This multi-step synthesis raises questions about the authenticity of what we’re seeing. Is it truly an image of a black hole, or is it an interpretation dressed up to look like one?

Adding to the skepticism, a team from the National Astronomical Observatory of Japan (NAOJ) recently reanalyzed the EHT data and came up with a different interpretation. Their version of the image presents an elongated shape with one side brighter than the other, likely due to the accretion disk rotating at a significant fraction of the speed of light.

The NAOJ scientists argue that the original EHT image could be flawed, not necessarily due to error, but because of the inherent uncertainties and assumptions built into the image reconstruction process. This alternate analysis suggests that we may be seeing more of the EHT team’s interpretation than an objective view of Sgr A* itself.

The EHT’s “image” of Sgr A* is undoubtedly a scientific feat, but it’s also a reminder of the interpretive nature of astrophysical data. When we look at this “picture” of a black hole, we are not gazing upon reality. Rather, it’s a complex blend of radio wave data, mathematical transformations, and artistic interpretation. The process is rigorous and grounded in science, yet it leaves ample room for alternate interpretations, as the NAOJ team’s findings show.

While the Event Horizon Telescope’s “image” has advanced our understanding of black holes, it also highlights the limitations of our observational tools. We’re still piecing together a puzzle that relies on physical and mathematical inferences and assumptions about phenomena we can’t directly observe. As technology advances, we may one day see a more definitive “picture” of Sgr A*. For now, we have a scientifically informed but inherently uncertain representation.

Jayson Adams is a technology entrepreneur, artist, and the award-winning and best-selling author of two science fiction thrillers, Ares and Infernum. You can see more at www.jaysonadams.com.