Reading between the lines to model the galaxy's center black hole—a flash from the shadows.


It's not always as it seems. An incandescent bulb produces light that appears continuous but really flickers 120 times per second. This fluttering is blurred and the appearance of steady light is just an illusion since the brain only interprets an average of the information it receives.

Black holes are opaque to light, yet the intense glow of fast circling gas has its own distinctive flicker.

Black holes are opaque to light, yet the intense glow of fast circling gas has its own distinctive flicker. Lena Murchikova, a William D. Loughlin Member at 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 faint flickering to create the most precise model of Sagittarius A* (Sgr A*), the black hole at the center of our own galaxy. This model provides information on the black hole's structure and motion.

For the first time, scientists have portrayed the whole process of how gas moves through the Milky Way's center, from being blasted off by stars to collapsing into the black hole, in a single model. The researchers came to the conclusion that the most plausible scenario for black hole feeding at the galactic center includes directly infalling gas from great distances rather than a sluggish siphoning off of orbiting material over an extended period of time by reading between the lines (or flickering light).

Murchikova said, "Black holes are the custodians of their own secrets. We rely on direct observation and high-resolution simulation to better comprehend these enigmatic things.

Karl Schwarzschild predicted the existence of black holes almost 100 years ago, based on Albert Einstein's new theory of gravity, but scientists have only recently begun to observe and study them.

A approach to examine black hole flickering on the timeframe of a few seconds, rather than a few minutes, was introduced by Murchikova in an article published in Astrophysical Journal Letters in October 2021. This development made it possible to quantify Sgr Acharacteristics *'s based on its flickering more precisely. 

White has been researching the specifics of what transpires to the gas close to black holes (where the strong effects of general relativity are significant) and how this impacts the light that is arriving to us. Some of his discoveries were summarized in an article published in the Astrophysical Journal earlier this year.

Ressler has worked for years to create the most accurate models of the gas surrounding Sgr A*. This has been accomplished by carefully monitoring the material that surrounding stars lose as it falls into the black hole and by directly inserting measurements of those stars into the simulations. 

His most recent efforts resulted in a publication published in the Astrophysical Journal Letters in 2020. The last step was to compare the observed flickering pattern of Sgr A* with the predictions made by the various numerical models developed by Murchikova, White, and Ressler.

Murchikova said, "The outcome turned out to be really intriguing. "For a very long time, we believed that we could essentially ignore the origin of the gas around the black hole.

We discovered that these models generate flickering patterns that are not compatible with the observations.

More realistically, the gas ingested by black holes is first released by stars close to the galactic center in Ressler's stellar wind model. This gas reproduces the proper pattern of flickering as it enters the black hole. "The model wasn't created with the goal of explaining this specific phenomena. Success was by no means a given, Ressler said. So, after years of effort, it was quite exciting to see the model thrive so significantly.

The quantity of light released by the black hole may alter second by second when flickering is studied, according to White, who made hundreds of observations in a single night. "But unlike a large-scale picture, this does not reveal the spatial arrangement of the gas. The constraints of each observation type can be lessened by combining them, resulting in the most accurate image."