First image of black hole in polarized light catches glimpse of its invisible forces

March 24, 2021
You've never seen a black hole in this light. (EHT Collaboration)

You've never seen a black hole in this light. (EHT Collaboration)

A collaboration of hundreds of researchers from around the world has published unprecedented imagery of a black hole that captures how the phenomenon looks in polarized light, clearly showing its magnetic fields.

Appearing March 24 in The Astrophysical Journal Letters, the image is a refined version of one that the same collaboration released April 10, 2019, not long after the existence of black holes was first confirmed, marking the first time an image of the phenomena was released to the public.

The black hole at hand is located in the center of the galaxy Messier 87. It has a mass of 6.5 billion times that of the sun and is 55 million light-years away from Earth. It also has a radio jet of material and light spewing from its center that extends 5,000 light-years, at minimum.

When the Event Horizon Telescope took the first picture of this black hole, it appeared as a reddish-orange light ring with a black circle in the center. The dark center is not lack of light, but rather light that humans cannot see because it marks the exit from the observable universe, where space-time collapses on itself.

The seemingly calm light ring is actually matter that is being ripped apart around this center of singularity. That chaotic release of energy creates a photon orbit, and those photons comprise the light of which the telescope detected polarization.

"The nature of what's producing the light, in this case, is synchrotron emission. So it's really relativistic electrons that are gyrating quickly around magnetic field lines," said study coauthor Andrew Chael, a NASA Hubble Fellow at the Princeton Center for Theoretical Science and the Princeton Gravity Initiative. "That means that it has a direction associated with it, as well as the total brightness." 

The new image is extremely similar to the initial one, except because it was run with polarized light detectors, it has striations on top of the colored part, which denote the hole's magnetic fields. The image was further reported in another paper published alongside the first. 

"What we see today is the same images two years ago in terms of intensity, but with these lines on top of it," Chael said, "which indicate the direction of the light and polarizations."

Magnetic fields are important to see because currently, knowledge of how matter and light move around the dark abyss with unimaginable gravitational force is based on hypothesis. In fact, most information about black holes is based on inference and theory, with a recent one surrounding the phenomena's existence at the beginning of time.

"The more we understand different parts of the physics of what's going on in this region, the better we can isolate them," Chael said. "If we really want to use the black hole images to make precise tests of general relativity, for example, we really want to know what's going on in the astrophysics of it and why certain regions are lighting up."

Normally, when the human eye is exposed to light it accepts numerous rays with lots of intensity; this is how people are used to experiencing light.

However, they are also well acquainted with polarized lenses or sunglasses. The lenses block out light rays moving in a particular direction as the waves are oscillating. Removing a direction of the light reduces glare and allows people with the glasses on to see other rays more clearly. 

"Sometimes if you look at your phone with polarized sunglasses and rotate it in a certain way, you might have the phone screen disappear," Chael said, conveying that polarizing light removes one specific oscillating ray. 

The telescope's recent results, similarly, show how the light waves are moving around the object by taking away some rays of light per image, then combining all the images for very clear pictures of how the waves are moving. Additionally, collections of photons in a patch of the image moving in a certain direction indicate a magnetic field in that direction.

The Event Horizon Telescope, or EHT, collaboration includes over 200 researchers and combines information from telescopes around the world, detecting various patterns in the M87 black hole. Piecing together the images, Chael says a conglomerate is formed.

"In the different telescopes of the EHT, we have, sort of, detectors that look at both components of the polarization — you can think of it like a vector," he said. "There's a component of the polarization that's sort of east, west and there's north, south. We have detectors that are sensitive to each of those, that take information to characterize the whole signal."

In addition to the conglomerate image, there is another image where the researchers zoom out from a single telescope's view to see the jet fleeing from the black hole on its own.

"We produce this very high resolution image of the circle and the core of the jet," Chael said. "But then, with individual telescopes, we can look at the larger scale structure — we can zoom out, and that's when we see the jet emergence." 

There are several theories for how this jet is powered, and Chael relayed that two famous ones are that it is either energized by the rotational energy of the black hole or by that of the disk, or light ring around it. However, he notes that in both cases, it is probably due to magnetic fields.

"When we had only a total intensity [version of the image], many [simulations] could explain the data," he said. "Now that we have polarization, only a few of them can. Now, we're able to really focus in on that set of models, and test them even more precisely in the future."

The papers, "First M87 Event Horizon Telescope Results VIII: Magnetic Field Structure Near The Event Horizon," and "First M87 Event Horizon Telescope Results VII: polarization of the ring," were published March 24 in The Astrophysical Journal Letters. They were authored by Kazunori Akiyama, Michael Titus, Jason SooHoo, John Barrett, Geoffrey B. Crew, Michael H. Hecht, Colin Lonsdale, Lynn D. Matthews, Kotaro Moriyama, Alan Rogers and Chet Ruszczyk, Massachusetts Institute of Technology Haystack Observatory; Hiroshi Nagai, Motoki Kino, Shiro Ikeda and Tomohisa Kawashima, National Astronomical Observatory of Japan; Angelo Ricarte, Jonathan Weintroub, Maciek Wielgus, Daniel C. M. Palumbo, Dominic W. Pesce, Ramesh Narayan, David J. James, Elizabeth Himwich, Richard Anantua, Vincent L. Fish, Lindy Blackburn, Katherine L. Bouman, Roger Brissenden, Paul M. Chesler, Sheperd S. Doeleman, Joseph Farah, Christian M. Fromm, Peter Galison, Zachary Gelles, Michael D. Johnson, James M. Moran and Alexander W. Raymond, Black Hole Initiative at Harvard University; Ed Fomalont, National Radio Astronomy Observatory; Juan Carlos Algaba, University of Malaya; Guang-Yao Zhao, Rocco Lico, José L. Gómez, Antxon Alberdi and Antonio Fuentes, Glorieta de la Astronomía s/n; Norbert Wex, J. Anton Zensus, Robert Wharton, Jan Wagner, Pablo Torne, Efthalia Traianou, Tuomas Savolainen, Alan L. Roy, Helge Rottmann, Eduardo Ros, Gisela N. Ortiz-León, Aristeidis Noutsos, Felix M. Pötzl, Karl M. Menten, Nicola Marchili, Nicholas R. MacDonald, Ru-Sen Lu, Jun Liu, Kuo Liu, Andrei P. Lobanov, Thomas P. Krichbaum, Michael Kramer, Dong-Jin Kim, Jae-Young Kim, Ramesh Karuppusamy, Michael Janssen, Walter Alef, Rebecca Azulay, Anne-Kathrin Baczk, Silke Britzen, Ralph P. Eatough and Lijing Shao, Max-Planck-Institut f¨ur Radioastronomie; Ken Young, Nimesh Patel, Greg Lindahl, Mark Gurwell, Raymond Blundell and Garrett K. Keating, Center for Astrophysics — Harvard & Smithsonian; Bart Ripperda and Jordy Davelaar, Flatiron Institute; Hung-Yi Pu, Jongho Park, Masanori Nakamura, Satoki Matsushita, Wen-Ping Lo, Shoko Koyama, Patrick M. Koch, Jun Yi Koay, Makoto Inoue, Chih-Wei L. Huang, Paul Ho and Keiichi Asada, Academia Sinica; Alejandro Mus Mejías and Iván Martí-Vidal, Universitat de Val`encia; Tyler Trent, Mel Rose, Dimitrios Psaltis, Feryal ¨Ozel, Lia Medeiros, Daniel P. Marrone, Junhan Kim, David Ball, Chi-kwan Chan, Pierre Christian, Buell T. Jannuzi and Arash Roshanineshat, University of Arizona; Mislav Baloković, Yale Center for Astronomy & Astrophysics; Mark G. Rawlings, Izumi Mizuno, Per Friberg, Dan Bintley, Jessica Dempse and Per Friberg, East Asian Observatory; Wilfred Boland, Nederlandse Onderzoekschool voor Astronomie; He Sun and Aviad Levis, California Institute of Technology; Ramprasad Rao, Geoffrey C. Bower and Ming-Tang Chen, Academia Sinica; Daryl Haggard and Hope Boyce, McGill University; Karl-Friedrich Schuster, Vincent Piétu, Roberto Neri, Carsten Kramer, Olivier Gentaz, Roberto García, Michael Bremer, Dominique Broguiere and Thomas Bronzwaer, Institut de Radioastronomie Millim´etrique; André Young, Daniel R. van Rossum, Freek Roelofs, Remo P. J. Tilanus, Héctor Olivares, Cornelia Müller, Monika Moscibrodzka, Alejandra Jimenez-Rosales, Sara Issaoun, Ciriaco Goddi, Raquel Fraga-Encinas, Christiaan D. Brinkerink and Heino Falcke, Radboud University; Jorge A. Preciado-López, Ue-Li Pen, Mansour Karami, Roman Gold and Avery E. Broderick, Perimeter Institute for Theoretical Physics; Paul Tiede, Chunchong Ni, Boris Georgiev and Britton Jeter, University of Waterloo; Bong Won Sohn, Sang-Sung Lee, Jongsoo Kim, Taehyun Jung, Do-Young Byun and Ilje Cho, Korea Astronomy and Space Science Institute; John E. Carlstrom, University of Chicago; Andrew Chael, Princeton University; Shami Chatterjee and James M. Cordes, Cornell University; Doosoo Yoon, Oliver Porth, Gibwa Musoke, Sera Markoff and Koushik Chatterjee, University of Amsterdam; Shan-Shan Zhao, Feng Yuan, Zhiqiang Shen, Wu Jiang, Lei Huang, Minfeng Gu and Yongjun Chen, Shanghai Astronomical Observatory, Chinese Academy of Sciences; Michael Lindqvist and John E. Conway, Chalmers University of Technology; Ziri Younsi, Luciano Rezzolla, Antonios Nathanail, Yosuke Mizuno, Alejandro Cruz-Osorio and Mariafelicia De Laurentis, Institut f¨ur Theoretische Physik; Mahito Sasada, Fumie Tazaki, Tomoaki Oyama, Hiroki Okino, Yutaro Kofuji, Mareki Honma, Kazuhiro Hada and Yuzhu Cui, National Astronomical Observatory of Japan; Roger Deane, University of the Witwatersrand; Iniyan Natarajan, Rhodes University; Gregory Desvignes, Sorbonne Université; Jason Dexter, University of Colorado, Boulder; George N. Wong, Ben Prather and Charles F. Gammie, University of Illinois; David Sánchez-Arguelles, David H. Hughes and Arturo I. Gómez-Ruiz, Instituto Nacional de Astrof´ısica, ´Optica y Electr´onica; Ronald Hesper, University of Groningen, Landleven; Luis C. Ho, Peking University; Alan P. Marscher and Svetlana Jorstad, Boston University; Huib Jan van Langevelde, Ilse van Bemmel, Des Small and Mark Kettenis, Joint Institute for VLBI ERIC (JIVE); Cheng-Yu Kuo, National Sun Yat-Sen University; Tod R. Lauer, National Optical Astronomy Observatory; Yan-Rong Li, Institute of High Energy Physics, Chinese Academy of Sciences; Zhiyuan Li, Nanjing University; Kazi L. J. Rygl and Elisabetta Liuzzo, Italian ALMA Regional Centre; Laurent Loinard, Instituto de Radioastronom´ıa y Astrofísica; Jirong Mao, Yunnan Observatories, Chinese Academy of Sciences; Venkatessh Ramakrishnan and Neil M. Nagar, Universidad de Concepción; F. Peter Schloerb, Aleksandar Popstefanija and Gopal Narayanan, University of Massachusetts; Joseph Neilsen, Villanova University; Michael A. Nowak, Washington University; Richard Plambeck, University of California; Salvador Sánchez, Instituto de Radioastronomía Milimétrica; Kenji Toma, Tohoku University; Sascha Trippe, Seoul National University; Derek Ward-Thompson, University of Central Lancashire; John Wardle, Brandeis University; Qingwen Wu, Huazhong University of Science and Technology; and Ye-Fei Yuan, University of Science and Technology of China. 

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