Astronomers map magnetic fields from a black hole


The black hole inside the galaxy Messier 87 (M87) did not just serve as a model for the first photo of a singularity: it helped reveal how magnetic fields act near the event horizon – the region from which nothing can escape the immense gravitational forces .

Natural light or that radiated by a lamp goes in all directions when it is emitted – that is why it illuminates around you, vibrating in infinite planes and in all directions. As the light advances, the two planes in which it forms (the electric and the magnetic) revolve around the axis of propagation. In polarized light, in turn, the electric and magnetic vibration planes do not rotate, and it only propagates in one plane.

To make natural light polarized, on Earth we use special lenses; in space, this happens when it is emitted in regions of high temperatures, where there are strong magnetic fields – as in the event horizon of a black hole. “The polarization of light carries information that allows us to better understand the physics behind the image we saw in April 2019,” said astrophysicist Iván Martí-Vidal.

Magnetic field

A mystery that has always intrigued astrophysicists is how a part of the matter that gives in to the gigantic gravitational forces of a singularity escapes moments before being swallowed, being launched into space in jets of energy that reach thousands of light years away (in the case of M87, five thousand light years beyond the galaxy).

From the image captured by the 11 telescopes that make up the Event Horizon Telescope (EHT) and its shadow in polarized light, it was possible for astronomers to understand the process by which the M87’s magnetic field pushes matter out – by doing so , the flow of matter and energy would be ejected thousands of light years beyond the black hole.

“The observations suggest that the magnetic fields at the edge of the black hole are strong enough to push hot gas and help it withstand the pull of gravity,” astrophysicist Jason Dexter told

As the charged gas particles revolve around the singularity, they strengthen the magnetic field – but the researchers realized that not all of it rotates with the gas that spirals towards the event horizon.

Against the tide

“We don’t see the same polarization map that we would expect if the magnetic fields were just surrounding the black hole, being dragged along with the gas. The field is strong because it can resist being swallowed up,” explained the astrophysicist.

Mapping the magnetic fields was not a very easy task: of all the light emitted by the black hole, only a small part is polarized.

“Digging up those relatively weaker signals and accounting for bigger errors was a huge effort,” said Dexter. According to the astrophysicist, the same observations can be made in the center of our own galaxy, where the black hole Sagittarius A * roars: “Learning more about the physical properties behind the image of the black hole in the galaxy Messier 87 is just the beginning.”


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