Magnetic fields at the edge of a black hole

Magnetic fields at the edge of a black hole
editorial staff
/ Press release from the Max Planck Institute for Radio Astronomy
March 25, 2021

The research team of the Event Horizon Telescope
(EHT) yesterday presented new observations of the region immediately around the supermassive black hole of the galaxy Messier 87. They could help explain how the galaxy can create a high-energy jet from its core. The decisive factor was the measurement of the polarized radio radiation from the area.

Polarization in the center of the galaxy M 87: The polarization “field lines” are plotted over an image of the total intensity (the image of the “shadow of a black hole” from April 2019). In order to highlight the regions with stronger polarization, the length and opacity of the lines were scaled with the polarized intensity. Enlarge image Polarization in the center of the galaxy M87.

image: EHT-CollaborationDuran / MPIfR [Groansicht]

On April 10, 2019, the very first image of a black hole was published, showing a light, ring-shaped structure with a dark central region – the shadow of the black hole. Since then, the scientists of the Event-Horizon.Telescope-Collaboration have further analyzed their data, which was collected by telescopes around the globe in 2017, and discovered that a significant proportion of the radio radiation is caused by the supermassive black hole in the heart of the 55 million light-years away galaxy M 87 is polarized.

“The polarization of light carries information that enables us to better understand the physics behind the picture we presented in April 2019,” explains Monika Mościbrodzka, coordinator of the EHT working group on polarimetry and assistant professor at Radboud University in the Netherlands. Electromagnetic radiation is polarized when it passes through certain filters, such as the lenses of polarized sunglasses, or when it is radiated into hot regions of space that are magnetized. Just as polarized sunglasses help us see better by reducing reflections and glare on bright surfaces, astronomers can sharpen their vision of the area around the black hole by examining how the light emitted from there is polarized.

In particular, the polarization allows the team to map the course of the magnetic field lines on the inner edge of the black hole. “This is the key to understanding the powerful jet that emanates from this region,” says Alan Roy, project scientist for VLBI (Very Large Baseline Interferometry) at the MPIfR-APEX telescope (Atacama Pathfinder Experiment) in northern Chile. The bright ray of energy and matter that emerges from the core of M87 and extends at least 100,000 light years from its center is one of the most mysterious and energetic constituents of this galaxy. Most of the matter that is near the edge of a black hole falls into it. However, some of the surrounding particles escape shortly before being captured and are blown far out into space in the form of a jet.

With the help of different model assumptions, the astronomers are trying to better understand how matter behaves near the black hole. But they still do not know exactly how a jet larger than the entire galaxy is launched from a very compact region in the center – comparable to the extent of the solar system. With the new EHT image of the black hole and its shadow in polarized light, the astronomers have for the first time succeeded in obtaining a key image of the launch mechanism in the order of magnitude in which the jet is formed.

In order to observe the very compact launch region of the jet in the heart of the M87 galaxy, the EHT collaboration combined eight telescopes all over the world, including APEX in Chile and the 30-meter IRAM telescope in Pico Veleta, Spain, to create a virtual one Telescope from Erdgre. The data were merged and processed on two special high-performance computers, so-called correlators, one of which is located at the Max Planck Institute for Radio Astronomy in Bonn. The impressive resolution of just 20 micro-arcseconds achieved with the EHT is equivalent to that required to measure the length of a credit card on the lunar surface.

This allowed the team to directly observe the shadow of the black hole and the surrounding ring of radiation, with the new image of the polarized radiation clearly showing that the ring is magnetized.

“The EHT is a fantastic facility for testing the laws of physics in a region of extreme gravity. It gives us a unique opportunity to tackle phenomena that we have never investigated before. Our future EHT observations will provide more information on the mystery Reveal the area of ​​space near the event horizons of supermassive black holes, “says J. Anton Zensus, founding chairman of the EHT collaboration and director at the Max Planck Institute in Bonn.

The results are presented in two separate articles in the journal
Astrophysical Journal Letters
published by the EHT collaboration project, which involves more than 300 researchers from various organizations and universities worldwide.


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