Understanding Black Holes

It is important to clarify that black holes themselves are invisible, as they do not emit light. When we talk about "seeing" a black hole, we refer to capturing the glowing ring of light surrounding its event horizon. Beyond this point, light is trapped and cannot escape into space. The luminous ring highlights the black hole's "shadow," which represents the most extreme phenomena known in the universe.

The intense plasma encircling the black hole can reach temperatures of up to 10 billion Kelvin (18 billion degrees Fahrenheit) and orbits a compact region roughly the size of Mercury's orbit around our sun. The surrounding matter is highly dynamic, changing as frequently as every five minutes during observations. In contrast to the larger M87 black hole, which has a mass of approximately 6.5 billion suns, Sagittarius A* is significantly smaller—less than one-thousandth of M87's mass—allowing it to change much more rapidly.

The Structure of Sagittarius A*

In their efforts to create this new image, researchers needed to discern which aspects of the black hole were stable and which were more variable. The aim was to uncover the underlying structure of Sagittarius A*.

The findings demonstrated that despite the significant differences in size and mass between the two black holes, they appear remarkably similar when viewed through a telescope. Interestingly, the data for both Sagittarius A* and M87* was collected simultaneously in 2017. However, the smaller size of Sagittarius A* posed challenges that delayed the formation of its image, as the plasma surrounding our galaxy’s center can distort the data.

As Chi-kwan Chan, an EHT scientist, noted, “The gas near the black holes travels at speeds nearly that of light. While it takes days or weeks to orbit the larger M87*, Sagittarius A* completes its orbit in just minutes, leading to rapid changes in brightness and patterns.”

The Data Journey

Though astronomers had previously noted stars orbiting Sagittarius A*, direct visual evidence of the black hole had yet to be obtained. The collaboration between M87* and Sagittarius A* resulted in 5 petabytes of data, which had to be distributed between two institutions—the Haystack Observatory and the Max Planck Institute for Radio Astronomy—for calibration. Various algorithms were employed to generate thousands of images from the raw data, with the average of these images forming the official representation of Sagittarius A*.

Each image contributes to our understanding of these extraordinary celestial objects, reinforcing predictions stemming from Einstein’s theory of relativity, which posits that black holes are the remnants of colossal, dying stars. The EHT aims to expand its network of telescopes in the coming years, enabling further imaging of black holes. Currently, the images we have are somewhat blurry and only capture the brightest regions; future advancements may allow us to see more subtle features that remain elusive for now.