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Curated by RSF Research Staff

New insights in the dynamic of black hole magnetic field

In 2015, for the first time, astronomers confirmed the existence of an intense magnetic field surrounding the event horizon of a supermassive black hole. This much-anticipated discovery fitted an important piece into the understanding of the way black holes affect the space around them. This discovery was of great importance because these magnetic fields are thought to power supermassive black holes. Also, it put decades of theoretical work on solid observational ground.

Black holes are far more complex than the common representation as huge galactic vacuum cleaners that suck in anything that gets too close. In reality, they are more like cosmic engines. They act like a convertor pumping matter and releasing intense radiation which can be blasted out across thousands of light-years in strong galaxy-shaping jets. And all this energy seems to be driven by the magnetic fields. So, understanding them is critical and nobody has been able to resolve magnetic fields near the event horizon until recently. A lot of mysteries remain and the galactic center appears to be a very dynamic place with magnetic fields dancing all over the place.

Event horizon, accretion disk and gamma ray jets of a black hole. The accretion disk can be seen, because the spinning particles are accelerated to tremendous speeds by the huge gravity of the black hole, releasing heat and powerful x-rays and gamma rays out into the universe as they smash into each other.

In 2017, another step was achieved in the understanding of the magnetic field around black holes while observing the accretion disk coronae around galactic black holes. It seemed these accretion disks are playing a role in systems showing relativistic jet outflows. Theoretical models predicted that the magnetic field was powering these jet outflows, and spectral models showed that the jet base was identical to the corona. Based on this theory, an international team led by Yigit Dallilar from University of Florida has measured the transient source V404 Cygni in search of a precise measurement of the magnetic field in the corona. Some very interesting data were captured using simultaneous infrared, optical, x-ray, and radio observations during the rapid synchrotron cooling of the 2015 outburst.

To observe it was something that happens once or twice in one's career. This discovery puts us one step closer to understanding how the universe works.

Thanks to these observations they were able to calculate a value of 461 ± 12 gauss for the magnetic field. However, this result was much lower than previous estimates by multiple order of magnitude which was providing answers but also new questions. These new data will help to update the current models of accretion physics in black holes and neutron star binary systems.

Our surprisingly low measurements will force new constraints on theoretical models that previously focused on strong magnetic fields accelerating and directing the jet flows. We weren't expecting this, so it changes much of what we thought we knew.

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