Reads between the lines to model the central black hole of our galaxy

Apparently can amount. The light from an incandescent bulb works constantly, but it flashes 120 times per second. Because the brain perceives only an average of the information it receives, this flicker is blurred and the perception of constant illumination is only an illusion.

Although light can not escape a black hole, the bright glow from fast-circulating gas (remember the pictures of the black hole of M87 and Sgr A *) has its own unique flicker. In a recent article, published in Astrophysical Journal Letters, Lena Murchikova, William D. Loughlin Member of the Institute for Advanced Study; Chris White of Princeton University; and Sean Ressler of the University of California, Santa Barbara were able to use this subtle flicker to build the most accurate model to date of our own galaxy’s central black hole – Sagittarius A * (Sgr A *) – providing insight into properties such as its structure and movement.

For the first time, researchers in a single model have shown the whole story of how gas moves through the center of the Milky Way – from being blown up by stars to falling into the black hole. Reading between the proverbial lines (or flickering lights), the team concluded that the most likely image of a black hole feeding in the galactic center involves gas falling directly from great distances, rather than sucking it off. slowly orbiting material over a long period of time. time.

“Black holes are guardians of their own secrets,” Murchikova said. “To better understand these mysterious objects, we rely on direct observation and high-resolution modeling.”

Although the existence of black holes was predicted about 100 years ago by Karl Schwarzschild, based on Albert Einstein’s new theory of gravity, scientists are only now beginning to study them with observations.

In October 2021, Murchikova published an article in Astrophysical Journal Letters, which introduces a method to study black hole flicker on a time scale of seconds instead of minutes. This progress enabled a more precise quantification of the properties of Sgr A * as a function of its scintillation.

White worked on the details of what happens to gas near black holes (where the strong effects of general relativity are important) and how it affects the light that reaches us. ONE Astrophysical journal the publication earlier this year summarizes some of his findings.

Ressler has spent years trying to build the most realistic simulations to date of the gas around Sgr A *. He did this by incorporating observations of nearby stars directly into the simulations and carefully tracing the material they release as it falls into the black hole. His recent work has resulted in one Astrophysical journal paper in 2020.

Murchikova, White, and Ressler then teamed up to compare the observed flicker pattern for Sgr A * with those predicted by their respective numerical models.

“The result turned out to be very interesting,” Murchikova explained. “For a long time, we thought we could pretty much ignore where the gas around the black hole came from. Typical models imagine a ring of man-made gas, roughly donut-shaped, at a great distance from the black hole. We found that such patterns produce flicker patterns that do not agree with observations. »

Ressler’s stellar wind model takes a more realistic approach, where gas consumed by black holes is initially expelled by stars near the galactic center. When this gas falls into the black hole, it repeats the correct pattern of flicker. “The model was not built for the purpose of explaining this particular phenomenon. Success was by no means a guarantee, ”commented Ressler. “So it was very encouraging to see the model succeed so spectacularly after many years of work.”

“When we study flicker, we can see changes in the amount of light emitted by the black hole second by second, taking thousands of measurements over a single night,” White explained. “However, it does not tell us how the gas is arranged in space, as a large-scale image would. By combining these two types of observations, it is possible to soften the boundaries of each one and thus achieve the most authentic image. »

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