Recent investigations into one of the first black holes ever imaged, known as M87*, have unveiled intriguing changes in its environment. These unexpected alterations, particularly in its magnetic fields, are becoming evident through polarized light observations. Polarized light consists of light waves that are oriented in a specific direction, whether vertically or horizontally. This new data is crucial for astronomers who are keen to understand the role of magnetic fields in the dynamics of black holes like M87*.
According to one of the study's co-authors, future research may include a sequence of images captured as frequently as once or twice a week, which could better illustrate the rapid changes occurring in M87*. Currently, with only three images available from the Event Horizon Telescope (EHT) collaboration, researchers are just beginning to delve into the complex mysteries surrounding this black hole.
The three images of M87* were taken in 2017, 2018, and 2021 by the EHT collaboration, a global network of radio telescopes. Recently, the EHT has expanded its network with two new observatories in Arizona and France. Located at the center of the galaxy Messier 87 (M87), M87* is approximately 55 million light-years from Earth and boasts a mass exceeding six billion times that of the sun.
With the new polarization data, scientists can gain insights into the structure and strength of the magnetic fields surrounding M87*. Theoretical models suggest that these magnetic fields exist within a plasma disk (superheated gas) orbiting the black hole. These fields can form magnetic towers filled with immense energy, which propel matter along jets moving at nearly the speed of light. Although these jets originate from a small area near the black hole, they significantly impact the galaxy's star formation and energy distribution, influencing overall galaxy evolution.
Sebastiano von Fellenberg, a scientist who was with Germany's Max Planck Institute for Radio Astronomy (MPIfR) during this research, highlighted two main findings. Firstly, the polarization exhibited considerable variability, while the total intensity images of M87* remained stable. This consistency in total intensity is expected, as it relates to the gravitational potential of the black hole, which should not fluctuate in a short time frame.
One of the most surprising discoveries was a polarization measurement observed in 2021, referred to as angle β₂. This measurement showed such a dramatic shift compared to previous readings from 2017 and 2018 that it no longer aligned with the electromagnetic-energy flux from those earlier years. Essentially, the polarization pattern flipped direction across the three images: it spiraled one way in 2017, stabilized in 2018, and then reversed in 2021.
Scientists are now working to understand this unexpected change. The discrepancy can only be explained if no additional polarization changes were caused by electrons or matter along the line of sight, a phenomenon known as external Faraday rotation. This leads researchers to consider four potential explanations: a change in the underlying magnetic field structure, a variation in the degree of Faraday rotation, evolving contributions from different emission regions (such as the disk or jet), or a combination of these factors.
As astronomers continue to study M87*, the insights gleaned from these observations may ultimately enhance our understanding of black holes and their surrounding environments, paving the way for future discoveries in the field of astrophysics.
