Two articles – available here and here – published in “The Astrophysical Journal Letters” report different aspects of a study that led to the representation of the area around the supermassive black hole at the center of the galaxy M87 in polarized light. Scientists from the Event Horizon Telescope Collaboration used data collected in 2017 to obtain a new image that offers new information on the structure of the magnetic fields around the supermassive black hole. A third article published in the same journal reports the details of the observations conducted with the ALMA radio telescope during the 2017 observation campaign.
After the famous image of the area around the supermassive black hole of the galaxy M87 was published, the scientists from the Event Horizon Telescope Collaboration continued to work on the huge amount of data collected. However, precisely because these are studies at the frontier of astronomy, the task following the creation of the first image took a very long time. Examining the polarization of emissions around the supermassive black hole at the center of the galaxy M87 allows them to investigate in greater depth the processes taking place in that truly extreme environment. In order to obtain this new image, they had to develop further data analysis techniques and subsequently compare them with computer simulations created using current models of supermassive black holes.
Several radio telescopes were used to collect the amount of data used to study the supermassive black hole at the center of the galaxy M87, but the Atacama Large Millimeter/submillimeter Array (ALMA), inaugurated in March 2013, once again proved to be a crucial instrument. In this case, ALMA obtained polarimetric measurements which made it possible to measure the polarization of the emissions. They can show an electromagnetic field oscillating in a plane in linear polarization or in a rotating plane in circular polarization. The image (Courtesy EHT Collaboration) shows the area around the supermassive black hole of the galaxy M87 in polarized light.
The results offer new insights into the magnetic fields around the supermassive black hole. The detected characteristics suggest that the accretion of the disk of materials around it is chaotic and therefore similar to the results of computer simulations. They also offer new, more precise, estimates of the temperatures of the gas near the event horizon, which is in the form of plasma at temperatures on the order of 10 billion Kelvin. This plasma tends to be repelled by magnetic fields, which help keep it outside the event horizon. Despite the immense gravity of a supermassive black hole, only a portion of that plasma gets swallowed.
Over the years, different models have been created to describe the physical processes taking place in the area around a supermassive black hole. The creation of the famous photo of the area around the one of the galaxy M87 already made it possible to carry out some checks, and now that work has gone on thanks to the polarization data.
The images published in recent years show the results of an enormous work that offers scientific advances and a way for further development. In the future, it will be possible to conduct new observation campaigns with a network of radio telescopes that in the meantime received upgrades and with the addition of other instruments. The data processing techniques developed for the Event Horizon Telescope project can also be improved to uncover the secrets of extreme objects such as supermassive black holes.
