Astronomers measured the magnetic fields of two supermassive black holes at the center of active galaxies and found that their strengths do not power the coronae.
Measuring A Supermassive Black Hole's Magnetic Field
The researchers used the data from the ALMA radio observatory in northern Chile to measure the strength of the magnetic fields around the two supermassive black holes in the active galactic nuclei IC 4329A, which is 200 million light-years away, and NGC 985, which is 580 million light-years away. This is the first time that anyone has measured magnetic fields around black holes, according to the researchers.
The team began measuring the magnetic fields using the ALMA radio observatory and then compared their data with observations from the VLA observatory in the United States and the ATCA observatory in Australia. Although the radio telescopes measured slightly different frequency bands, the researchers were able to confirm that there was an excess of radio emission from the synchrotron radiation.
"The surprise is that although we confirmed the emission of radio synchrotron radiation from the corona in both objects, it turns out that the magnetic field we measured is much too weak to be able to drive the intense heating of the coronae around these black holes," explained Yoshiyuki Inoue, lead author of the study.
From the data they have collected, the researchers deduced that the coronae were the size of about 40 Schwarzschild radii from the central black holes and had the strength around 10 gauss.
Black Holes Remain A Mystery
Now that scientists from RIKEN, a research institute, and the Japan Aerospace Exploration Agency (JAXA) found that the magnetic fields of supermassive black holes do not necessarily power their coronae, the questions regarding the exact mechanism behind the phenomenon remain.
The scientists said that they will continue probing the environment around supermassive black holes to understand the cosmic event. Inoue shared that his team will next look for signs of powerful gamma rays that accompany radio emissions.
Their findings were published in The Astrophysical Journal.