Incredible First View Of The Magnetic Fields Around Our Galaxy’s Supermassive Black Hole

The team that gave us the first-ever image of a black hole has released a new image of Sagittarius A*, the supermassive black hole at the center of the Milky Way, this time seen in polarised light for the first time. The image has captured the magnetic field structures spiraling around the black hole, similar to those seen around M87*, suggesting "strong, twisted, and organized" magnetic fields might be common among black holes.

The Event Horizon Telescope is a collaboration that uses radio telescopes around the world to form a combined array the size of Earth, large enough to image a black hole. If your eye had the same resolution, you could see a donut on the surface of the Moon. It's given us the first image of our own Sagittarius A* (Sgr A*) and the much larger and more powerful black hole at the center of the massive elliptical galaxy Messier 87. In 2021 it captured M87*'s magnetic fields, the first ever for a black hole, using polarized light.

Now the team has used the polarization of light to image the magnetic fields of Sgr A* for the first time. Light is made by oscillating electromagnetic waves and if it is oscillating in a preferred direction we call it polarized. This is how 3D glasses work – the two lenses have different polarization that let in only part of the light so our brains can create a 3D picture in our head. Polarized light helps reduce glare from bright light sources, which allowed the team to have a sharper view of the edge of the black hole and to map the magnetic field lines present there.

“For the first time, we have obtained polarimetric images at the event horizon scale of the black hole at our Galaxy's center, Sgr A*," Professor Mariafelicia De Laurentis, EHT Deputy Project Scientist and professor at the University of Naples Federico II.

"Thanks to the polarization of light, these images reveal a surprisingly detailed and orderly magnetic structure around the black hole. It is important that these images are offered in polarized light because it allows us to "see" and understand the geometry of the magnetic field around the black hole, a crucial aspect that cannot be captured with non-polarized light alone."

The plasma around a supermassive black hole moves along the magnetic field lines as plasma is made of charged particles. The whirling of these particles creates a polarization pattern on the light that is perpendicular to the magnetic field. Measuring the polarization tells us exactly how the magnetic field is wrapping around the supermassive black hole.

“Polarization matters in the study of black holes because it provides us with information about the geometry and dynamics of the magnetic fields surrounding the black hole," Professor De Laurentis explained. "These fields play a key role in accretion processes and jet emissions, directly influencing the observation of black holes and our understanding of the physics governing these extreme objects.”

Accretion and jet emissions are not things our friendly neighborhood supermassive black hole tends to partake in much. As black holes go, Sagittarius A* is fairly quiet and calm, which is a good thing because even at 26,000 light-years away, an active supermassive black hole can have an impact. These objects can shape the destiny of a whole galaxy.

But for M87*, those magnetic fields are key to the release of powerful jets. The supermassive black hole has been observed releasing jets of particles moving at almost the speed of light extending for about 5,000 light-years from M87*. Seeing the same magnetic structures that power far-reaching events in M87 in our own supermassive black hole suggests these are underlying mechanisms shared by all black holes.

“These magnetic fields are pivotal in controlling the accretion of matter into black holes and the ejection of energetic jets, which are among the most spectacular phenomena in the universe," Professor De Laurentis told IFLScience. "Understanding these fields allows us to probe the extreme conditions near black holes, testing theories of gravity and magnetohydrodynamics in regimes where the effects of Einstein's general relativity play a crucial role.”

This image of Sagittarius A* is another step forward in better understanding black holes and how they affect their host galaxies, as well as a fantastic test bed for theoretical models of black hole activities.

“These observations represent a technical milestone, showcasing the capabilities of current astronomical instruments and methodologies. They set a precedent for future observational campaigns and theoretical studies, pushing the boundaries of our understanding of the universe,” Professor De Laurentis.

The next-generation Event Horizon Telescope will be even better.

The studies are published in two papers in The Astrophysical Journal Letters.