294
Recent results from the EHT collaboration have revealed strong, organized magnetic fields around Sagittarius A*, suggesting common features of black holes. Detailed comparisons with the black hole M87 show similarities, hinting at the universal characteristics of a black hole. Future improvements in observational technology promise a deeper understanding and more detailed imaging of black holes.
Strong magnetic fields spiraling at the edge of Sagittarius A*
Earlier this year, the Event Horizon Telescope (EHT) collaboration published a new image showing strong, organized magnetic fields spiraling from the edge of the supermassive black hole Sagittarius A* (Sgr A*). This revolutionary image of the Milky Way's central black hole, taken for the first time in polarized light, shows a magnetic field structure remarkably similar to that of the black hole in galaxy M87.
This suggests that strong magnetic fields may be a common feature of all black holes. The similarity also increases the probability of a hidden jet from Sgr A*. These findings were published in The Astrophysical Journal Letters .
Comparative analysis: Sgr A* and M87
In 2022, scientists released the first image of Sgr A*, which is about 27 light-years from Earth, showing that although the Milky Way's supermassive black hole is more than a thousand times smaller and less massive than M000, it looks remarkably similar. . This has led scientists to wonder if they have anything in common other than their appearance. To find out, the team decided to study Sgr A* in polarized light.
Previous studies of the light around M87* have shown that the magnetic fields around the giant black hole have allowed it to launch powerful jets of material back into its environment. Building on that work, the new images showed that the same may be true for Sgr A*.
The role of magnetic fields in the dynamics of a black hole
"What we're seeing now is that there are strong, distorted and organized magnetic fields near the black hole at the center of the Milky Way galaxy," said Sarah Issaun, NASA Hubble Einstein Program Fellow, Smithsonian Astrophysical Observatory (SAO). ) astrophysicist and co-head of the project. "In addition to Sgr A* having a strikingly similar polarization pattern to that seen in the much larger and more powerful black hole M87*, we have learned that strong and ordered magnetic fields are critical to how black holes interact with gas and substance around. their".
Polarized Light: A Tool for Solving Black Hole Mysteries
Light is an oscillating or moving electromagnetic wave that allows us to see objects. Sometimes light oscillates in a desired orientation, and we call it "polarized." Although polarized light is all around us, it is indistinguishable from "normal" light to the human eye. In the plasma around these black holes, particles rotating around the lines of force of the magnetic field form a polarization perpendicular to the field. This allows astronomers to see in increasingly vivid detail what is happening in the regions of black holes and to map their magnetic field lines.
"By imaging polarized light from hot gas glowing near black holes, we directly infer the structure and strength of the magnetic fields that create the flow of gas and matter that the black hole feeds on and ejects," said Harvard Black Hole Initiative Fellow and Co-Director project of Angelo Ricart. "Polarized light teaches us a lot more about astrophysics, the properties of the gas, and the mechanisms that take place when feeding a black hole."
Technological challenges and advances in black hole imaging
But imaging black holes in polarized light isn't as easy as putting on a pair of polarized sunglasses, and that's especially true for Sgr A*, which changes so quickly that it doesn't linger in images. Imaging a supermassive black hole requires more sophisticated instruments than those previously used to capture M87*, a much more persistent target.
CfA PhD student and SAO astrophysicist Paul Thiede said: "It's great that we were able to take a polarized image of Sgr A* at all. The first image required months of careful analysis to understand its dynamic nature and reveal its average structure. Creating a polarized image complicates the dynamics of magnetic fields around a black hole. Our models often assumed highly turbulent magnetic fields, which made it difficult to construct a polarized image. Fortunately, our black hole is much calmer, making the first image possible."
Future perspectives: expanding black hole research
Scientists are excited to get images of both supermassive black holes in polarized light because these images and the data they provide provide new ways to compare and contrast black holes of different sizes and masses. As imaging technology improves, it is likely to reveal even more mysteries about black holes and their similarities or differences.
Michi Baubeck, a postdoctoral researcher at the University of Illinois at Urbana-Champaign, said: “M87* and Sgr A* differ in several important ways: M87* is much larger, and it is absorbing material from its environment much faster. . So we might expect the magnetic fields to look quite different as well. But in this case, they turned out to be quite similar, which may mean that this structure is common to all black holes. A better understanding of the magnetic fields near black holes helps us answer several open questions, from how the jets form and launch to how powerful the bright flares we see in infrared and X-ray light are."
Improvement of black hole imaging methods
The EHT has made several observations since 2017 and plans to observe Sgr A* again in April 2024. The images improve every year as the EHT includes new telescopes, greater bandwidth, and new observing frequencies. A planned expansion over the next decade will allow for high-quality videos of Sgr A*, may reveal a hidden jet, and allow astronomers to observe similar polarization characteristics in other black holes. Meanwhile, extending the EHT into space will provide sharper images of black holes than ever before.
The CfA is leading several major initiatives aimed at dramatically increasing EHT over the next decade. The Next Generation EHT (ngEHT) project is undertaking a transformational upgrade of the EHT aimed at bringing several new radio dishes online, enabling simultaneous multi-color observations and increasing the overall sensitivity of the array. The ngEHT extension will allow the array to create real-time movies of supermassive black holes at the scale of the event horizon. These movies will allow us to dissect the detailed structure and dynamics near the event horizon, drawing attention to the features of the "strong field" of gravity predicted by general relativity, as well as the interaction of accretion and relativistic jet launch that forms large-scale structures in the universe.
Meanwhile, the Black Hole Explorer (BHEX) mission concept will extend the EHT into space, producing the sharpest images in the history of astronomy. BHEX will detect and image the "photon ring," a sharp ring formed by strongly lensed radiation around black holes. The properties of a black hole are reflected in the size and shape of the photon ring, revealing the masses and spins of dozens of black holes, in turn showing how these strange objects grow and interact with their host galaxies.
