The giant black hole at the heart of our galaxy is flickering – why it matters

At the heart of our galaxy lies a monstrous black hole called Sagittarius A*. Almost all galaxies have such supermassive black holes at their centers, and our particular black hole had its moment of fame in May 2022, when the Event Horizon Telescope project managed to snap a picture of it as part of an international collaboration. This image doesn’t actually show the black hole itself, which is invisible because it absorbs light. Instead, the image shows the gas around the black hole collapsing around the black hole’s event horizon and getting hot, releasing energy that can be seen by telescopes.

However, the glow of the gas around this black hole is not constant. In fact, it flickers, and scientists are studying that flickering to learn more about the structure of the black hole. As detailed in a paper published in the Astrophysical Journal Letters, researchers used this flicker to create the most accurate model of Sagittarius A* yet (via Institute of Advanced Studies). They were able to figure out how gas moves around and into the black hole and found that much of the material ingested comes from a considerable distance rather than eating up the nearby gas swirling around the black hole. “Black holes are the gatekeepers of their own secrets,” said lead researcher Lena Murchikova. “To better understand these mysterious objects, we rely on direct observation and high-resolution modeling.”

Working with the flicker

The current paper brings together the expertise of three experts who have worked to explore different aspects of Sagittarius A*. By combining large-scale observations of how nearby stars are affected by the black hole’s gravity with more detailed models of what happens to the gas near the black hole, they were able to see that the traditional understanding of black holes was incorrect. “For a long time we thought that we could largely ignore where the gas around the black hole came from,” says Murchikova. “Typical models envision an artificial ring of gas, roughly shaped like a doughnut, located some distance from the black hole. We found that such models produce flicker patterns that are inconsistent with observations.”

To explain the flare they saw, the experts had to assume that the gas falling into the black hole came from nearby stars, and not just the gas that orbited nearby. The stars near the center of the galaxy emit this gas, which is then drawn towards the black hole and finally past the event horizon. “By examining the flickering, we can see changes in the amount of light the black hole emits second by second and take thousands of measurements over the course of a single night,” said co-author Chris White. “But that doesn’t tell us how the gas is arranged in space like a large format image would. By combining these two types of observations, it is possible to mitigate the limitations of both and thus obtain the most authentic picture possible.” The giant black hole at the heart of our galaxy is flickering – why it matters


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