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Astronomers Capture Magnetic Fields Around Massive Black Hole

New images of magnetic fields and polarization around a black hole 55 million light years away confirm theories about the astronomical wonders.

(CN) — The outer edges of the black hole in the center of the Messier 87 galaxy include magnetic fields never before detected, until now, according to new research published Wednesday.  

The Event Horizon Telescope (EHT) collaboration that is responsible for the first image of a black hole, discovered in 2019, has released an image depicting in polarized light how the massive object in the center of M87 galaxy looks, detailing for the first time ever magnetic fields previously unknown.

This is the first time astronomers have been able to measure polarization, a signature of magnetic fields, this close to the edge of a black hole.  Their research was published Wednesday in several papers in the Astrophysical Journal.

These observations are significant in explaining how enormous energetic jets are launched from the massive core of the M87 galaxy, located 55 million light years away.

“One exciting part of this result, for me, is that it strongly favors a type of model for the gas flowing into the black hole that is called a MAD model - this is an acronym for ‘magnetically arrested disk,’” said Charles Gammie, Donald Biggar Willett Professor of Physics at the University of Illinois.

“In MAD models, the black hole pulls in as much magnetic field as it possibly can, until the field is just on the verge of breaking out and pushing back the inflowing gas,” Gammie added. “A competing class of models is called SANE - standard and normal evolution - and they are weakly magnetized. They don't look like what we see in the data.”

The Event Horizon Telescope (EHT) collaboration, who produced the first ever image of a black hole released in 2019, has today a new view of the massive object at the centre of the Messier 87 (M87) galaxy: how it looks in polarised light. This is the first time astronomers have been able to measure polarisation, a signature of magnetic fields, this close to the edge of a black hole.  This image shows the polarised view of the black hole in M87. The lines mark the orientation of polarisation, which is related to the magnetic field around the shadow of the black hole.

To get the image of the black hole, the collaboration linked eight telescopes around the world to create a virtual Earth-sized telescope, known as the EHT. The resolution obtained from the EHT, the researchers say, is roughly equivalent to what would be needed to measure the length of a credit card on the surface of the moon.

“This breakthrough could not have happened without worldwide collaboration--to make many telescopes around the world function as if they were one,” said study author Angelo Ricarte, an Institute for Theory and Computation Fellow at Harvard & Smithsonian's Center for Astrophysics.

Another author of the research, George Wong, Ph.D. student in physics at the University of Illinois Urbana–Champaign, said in an email that he is “incredibly happy that we are finally publishing this result, after much work from all members of the collaboration.”

“Not much is known about the conditions near the M87 black hole and having extra information about the strength and structure of the magnetic fields will help us to constrain our models and better understand the connection between M87's famous jet and the black hole,” Wong wrote.

Wong added that “as a theorist, it's very exciting to be able to compare our models to reality.”

“A lot of what I worked on, with collaborators at my institution and around the world, involved generating over 100,000 numerically simulated images to compare against the observed data,” he said. “We found that the best matches were so-called ‘MAD’ models, where the strength of the magnetic field near the event horizon becomes large enough that it can balance out the inward force of gravity from the black hole.”

In line with the MAD model, Wong went on to say that his team is “starting to find observational evidence that supports the theory that we can get energy out of a black hole!”

He continued: “I think this kind of question – ‘can we see energy being extracted from a black hole?’ – will drive a large part of future observational black hole science.” 

The jets of energy and matter that shoot out from M87’s core to extend at least 5,000 light-years from its center are among the galaxy’s most enigmatic and powerful features, researchers say.

The black hole is larger than the Earth’s solar system. Most matter near the edge falls in. But some particles, moments before capture, are instead blown far out into space as bright and powerful jets.

Astronomers have relied on different models theorizing how matter behaves near the black hole to better understand the process, but much remains to be understood.

With the new EHT image of the black hole and its shadow in polarized light, astronomers have the chance for the first time to look into the matter surrounding the black hole and research the interplay between matter flowing in and shooting out.

"We are now seeing the next crucial piece of evidence to understand how magnetic fields behave around black holes, and how activity in this very compact region of space can drive powerful jets that extend far beyond the galaxy," Monika Moscibrodzka, coordinator of the EHT Polarimetry Working Group and Assistant Professor at the Netherlands’ Radboud University, said in a press release.

Two years ago, the first-ever images of a black hole were released from EHT. The images showed a bright circular structure with a dark middle region known as the shadow of the black hole. The EHT collaboration has delved even deeper since then into the makeup of the object in the center of the M87 galaxy and have discovered that a significant portion of the light surrounding the black hole is polarized. 

“This work is a major milestone,” Ivan Marti-Vidal, coordinator of the EHT Polarimetry Working Group and researcher at Spain’s University of Valencia, said in the press release. “Unveiling this new polarized-light image required years of work due to the complex techniques involved in obtaining and analyzing the data.”

As with polarized sunglasses, light becomes polarized when it goes through certain filters. In space, polarization happens in hot regions where magnetic fields are present. Astronomers can learn about black holes and the areas surrounding them by researching how the light coming from them is polarized.

The newly published images “are key to understanding how the magnetic field allows the black hole to ‘eat’ matter and launch powerful jets,” Andrew Chael, an EHT collaboration member and NASA Hubble Fellow at the Princeton Center for Theoretical Science, said in the press release.

“Amazingly, a lot of this work happened during the pandemic,” Ricarte said in an email. “I find it incredible what we can accomplish, even under these difficult circumstances, if scientists around the world work together.”

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