Following the mind-boggling release of the first image ever captured of a black hole, astronomers have done it again, revealing a new view of the massive celestial object and shedding light on how magnetic fields behave close to black holes.
In 2019, the Event Horizon Telescope (EHT) collaboration produced the first-ever image of a black hole, which lies at the center of the M87 galaxy 55 million light-years from Earth. The image showed a bright ring with a dark center, which is the black hole's shadow. In capturing this image, astronomers noticed a significant amount of polarized light around the black hole. Now, the collaboration has revealed a new look at the black hole, showing what it looks like in polarized light.
Polarized light waves have a different orientation and brightness compared with unpolarized light. And, just like how light is polarized when it passes through some sunglasses, light is polarized when it's emitted in magnetized and hot areas of space.
As polarization is a signature of magnetic fields, this image makes it clear that the black hole's ring is magnetized. This polarized view "tells us that the emission in the ring is most certainly produced by magnetic fields that are located very close to the event horizon," Monika Moscibrodzka, coordinator of the EHT Polarimetry Working Group and assistant professor at Radboud Universiteit in the Netherlands, told Space.com.
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This is the first time that astronomers have been able to measure polarization so close to the edge of a black hole. Not only is this new view of this black hole spectacular to look at, but the image is revealing new information about the powerful radio jets shooting from M87.
"In the first images, we showed intensity only," Moscibrodzka said about the first-released image of the object. "Now, we add polarization information on the top of that original image."
"The new polarized images mark important steps towards learning more about the gas near the black hole, and in turn how black holes grow and launch jets," Jason Dexter, Assistant Professor at the University of Colorado Boulder and coordinator of the EHT Theory Working Group, told Space.com in an email.
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To capture the black hole, the collaboration used eight telescopes from around the world, combining their power to create a virtual Earth-sized telescope (the EHT).
"The radio telescopes of the EHT have receivers that record the sky signal in polarized light," Ivan Marti-Vidal, also a coordinator of the EHT Polarimetry Working Group and GenT Distinguished Researcher at the Universitat de Valencia in Spain, told Space.com. "These polarized receivers work in a way similar to that of the polarized sunglasses that some people use."
By showing the black hole in M87 through polarized light, the team got a better look at the object's event horizon, which is also known as the "point of no return" because it's the point at which no matter can get closer to the black hole without being pulled in. They also were able to better study the interaction with the object's accretion disk, which is a disk of hot gas and other diffuse material that falls in toward a black hole and swirls around it.
The team's observations and this new view of the object in M87 is deepening scientists' understanding of the structure of magnetic fields just outside of a black hole, as it has remained a mystery how jets larger than the galaxy itself are emitted from the black hole at its heart.
"Astronomers have long thought that magnetic fields carried by the hot gas near black holes play an important role in letting the gas fall in, and in launching relativistic jets of energetic particles out into the surrounding galaxy. The polarized image we see tells us about the structure and strength of these magnetic fields very close to the black hole in M87, where the jet is launched," Dexter said.
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But these observations didn't just reveal magnetic fields on the edge of the black hole in M87, they also show that the gas there is very strongly magnetized.
"The main finding is that we not only see the magnetic fields near the black hole as expected, but they also appear to be strong. Our results indicate that the magnetic fields can push the gas around and resist being stretched. The result is an interesting clue to how black holes feed on gas and grow," Dexter added.
"We still don't know all the details of how jets are generated, but we know that magnetic fields may play a critical role," Marti-Vidal said. Going forward, the team hopes to continue observing M87, they told Space.com, not just in polarization but also "at different wavelengths [of light], to build a more complete picture of the black hole's surroundings and probe [the] magnetic fields in more detail," they added.
This work was published today (March 24) in two papers in The Astrophysical Journal Letters by the EHT collaboration, which involved over 300 researchers from organizations around the world. You can find the papers here and here.
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