The Event Horizon Telescope (EHT) collaboration released the first image of Sagittarius A*, the supermassive black hole at the center of the Milky Way, on May 12, 2022. The image shows a bright, lumpy ring of light surrounding a dark shadow, confirming that Einstein’s Theory of General Relativity governs the physics of our own galaxy’s core.
Why was imaging Sagittarius A* more difficult than M87*?
Astronomers expected the nearest supermassive black hole to be the easiest subject to photograph. However, the scale and speed of Sagittarius A* created significant technical hurdles that were not present when the EHT imaged M87* in 2019.
M87* is approximately 6.5 billion solar masses, making it vastly larger than Sagittarius A*, which is roughly 4 million solar masses. This size difference directly impacts how quickly the surrounding environment changes. According to EHT scientist Chi-kwan Chan, gas orbits the larger M87* in days or weeks, whereas in the smaller Sagittarius A*, an orbit can be completed in mere minutes.
The innermost orbit of Sagittarius A* takes about 30 minutes, compared to roughly 30 days for M87*. This rapid movement means the source flickers and rearranges itself while the telescopes are actively observing it. MIT Haystack’s Vincent Fish described the challenge as a data problem where the subject is “jumping all over the place,” comparing the difficulty to trying to photograph a fidgeting child in low light.
The light captured in the Sagittarius A* image is ancient. The photons left the galactic center tens of thousands of years ago, and the raw data used to create the image was recorded in April 2017.
How did the data confirm Einstein’s theories?
The resulting image features a bright emission ring with a measured diameter of approximately 51.8 microarcseconds. This measurement aligns closely with the size predicted by general relativity based on the known mass-to-distance ratio of the black hole.
EHT Project Scientist Geoffrey Bower stated the team was “stunned” by how well the ring size matched predictions from Einstein’s Theory of General Relativity. This confirmation is strengthened by the fact that two black holes of vastly different scales—M87* and Sagittarius A*—both fit the same mathematical framework.
Sera Markoff, co-chair of the EHT Science Council, noted that this consistency suggests General Relativity governs these objects up close. She explained that any observed differences in the appearance of black holes likely stem from the surrounding material rather than a failure of the theory itself. While an independent reanalysis by Miyoshi and colleagues questioned aspects of the ring, the EHT collaboration maintains that the ring with a central depression is the most accurate model for the data.
Comparison of Key Black Hole Data
| Feature | Sagittarius A* | M87* |
|---|---|---|
| Mass (Solar Masses) | ~4 million | ~6.5 billion |
| Approx. Orbit Time | ~30 minutes | ~30 days |
| Location | Milky Way Center | Messier 87 |
What are the future trends in black hole observation?
The ability to resolve Sagittarius A* changes the trajectory of galactic research. Because the black hole’s appearance shifts on timescales of minutes, researchers are moving away from static images toward dynamic observation.
The next major milestone involves creating “movies” of black holes. Instead of a single still frame, scientists aim to track the movement of plasma as it orbits the event horizon. EHT scientist Keiichi Asada stated that this capability will allow the team to go much further in testing how gravity behaves in extreme environments.
This shift from snapshots to video will provide a real-time look at the most violent environments in the universe. As Harvard-Smithsonian’s Michael Johnson noted in 2019, there is “almost no wiggle room” for Sagittarius A*, making it a high-precision laboratory for testing the limits of physics.
To follow the latest updates on black hole imaging, monitor the official Event Horizon Telescope Collaboration releases, as they provide the rawest scientific data before it is interpreted by mainstream media.
Frequently Asked Questions
How far away is Sagittarius A*?
Sagittarius A* is located approximately 27,000 light-years away from Earth at the center of the Milky Way galaxy.
What is the “shadow” in the black hole image?
The dark patch in the center of the ring is the shadow cast by the black hole, representing the area where light is captured by the event horizon.
How was the image created?
The image was produced by linking eight radio observatories across the planet to create an Earth-sized virtual telescope, a process known as Very Long Baseline Interferometry (VLBI).
What do you think is the most exciting part of seeing our galaxy’s center? Let us know in the comments below, or subscribe to our newsletter for more deep dives into space exploration.
