The supermassive black hole, Sagittarius A* (Sgr A*), sitting at the center of the Milky Way, may not be as active as some other galaxies’ black holes, but it is definitely an enigmatic and savage creature. Recent observations by astrophysicists Gustavo Magallanes-Guijón and Sergio Mendoza from the National Autonomous University of Mexico have revealed a truly intriguing behavior of Sgr A* – it pulsates. Like clockwork, every 76 minutes, the gamma-ray flux emitted by the black hole fluctuates, indicating a periodic motion of an unknown object around it. These findings, currently awaiting peer review, are documented on the preprint server arXiv.
Black holes themselves do not emit detectable radiation. They are essentially pitch-black voids, invisible to our telescopes. However, the space surrounding them tells a different story. In the extremely gravitational environment near the event horizon of a black hole, interesting phenomena can occur. Sagittarius A* emits light across various wavelengths, and the intensity of this light changes significantly over time. In some of these wavelengths, astronomers have observed a peculiar pattern. For instance, radio waves showed fluctuations with a period of about 70 minutes, as reported in a 2022 paper. Additionally, a 2017 study revealed a periodicity of 149 minutes in the black hole’s X-ray emissions, which is twice that of the radio waves. Now, the gamma-ray fluctuations exhibit a similar periodicity to the radio and X-ray emissions.
Exploring the Gamma-ray Data
In 2021, the connection between gamma radiation and Sgr A* was finally established with confidence. Capitalizing on this breakthrough, Magallanes-Guijón and Mendoza decided to examine the gamma-ray data more closely. They sourced publicly available data from the Fermi Gamma-ray Space Telescope, spanning from June to December 2022, and subjected it to thorough analysis. Their efforts paid off as they identified a clear periodic pattern. According to their results, Sgr A* emits a flare of gamma radiation every 76.32 minutes. Gamma radiation represents the most energetic range of light in the Universe. The striking similarity between the periodicity of these gamma-ray flares and the radio and X-ray flares strongly suggests an underlying common cause.
Since black holes emit no radiation themselves, regular and repeated periodicities often indicate the presence of an object in orbit around them. The 2022 paper mentioned earlier proposes that this object is likely a blob of hot gas held together by a powerful magnetic field. As particles within the gas experience synchrotron acceleration, they emit radiation, creating the observed flares. With an orbital distance similar to that of Mercury around the Sun, this gas blob orbits Sgr A* at astonishing speeds, roughly 30% of the speed of light. Magallanes-Guijón and Mendoza’s findings strongly support this interpretation, as they are consistent with the radio data and indicate that the gas blob emits radiation across multiple wavelengths.
Unraveling the Mysteries
However, many questions remain unanswered. Black holes pose significant challenges when it comes to studying them, and Sgr A* is no exception. Further observations across various wavelengths are needed to gain a better understanding of the intricate workings of this celestial object. By shedding more light (pun intended) on the dark heart of our Milky Way, we may unlock the secrets hidden within the supermassive black hole.
The surprising discovery of the pulsating behavior of Sgr A*, the supermassive black hole residing at the center of our galaxy, has provided scientists with valuable insights. Observations of its gamma-ray emissions at regular intervals suggest the presence of an object orbiting this black hole. While much uncertainty remains, continued research and observations hold the promise of unraveling the mysteries surrounding this captivating phenomenon.