April 22, 2024

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Astronomers detect strong magnetic fields billowing at the edge of the Milky Way's central black hole

Astronomers detect strong magnetic fields billowing at the edge of the Milky Way's central black hole

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The Event Horizon Telescope (EHT) team, which produced the first-ever image of our Milky Way's black hole released in 2022, has captured a new view of the massive object at the center of our galaxy: what it looks like in polarized light. This is the first time astronomers have been able to measure polarization, a hallmark of magnetic fields, near the edge of Sagittarius A*. This image shows the polarized view of a black hole in the Milky Way. The lines indicate the direction of polarization associated with the magnetic field around the black hole's shadow. Credit: EHT Collaboration

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The Event Horizon Telescope (EHT) team, which produced the first-ever image of our Milky Way's black hole released in 2022, has captured a new view of the massive object at the center of our galaxy: what it looks like in polarized light. This is the first time astronomers have been able to measure polarization, a hallmark of magnetic fields, near the edge of Sagittarius A*. This image shows the polarized view of a black hole in the Milky Way. The lines indicate the direction of polarization associated with the magnetic field around the black hole's shadow. Credit: EHT Collaboration

A new image from the Event Horizon Telescope (EHT) collaboration involving scientists from the Center for Astrophysics | Harvard and Smithsonian (CfA) have detected strong, organized magnetic fields billowing from the edge of the supermassive black hole Sagittarius A* (Sgr A*).

This new image of the monster lurking at the heart of the Milky Way, seen in polarized light for the first time, reveals a magnetic field structure strikingly similar to that of the black hole at the center of the galaxy M87, suggesting the presence of a strong magnetic field. Fields may be common to all black holes. This similarity also suggests the presence of a hidden jet in Sgr A*.

The results were published in Astrophysical Journal Letters.

Scientists revealed the first image of Sgr A* – which is about 27,000 light-years from Earth – in 2022, revealing that although the Milky Way's supermassive black hole is a thousand times smaller and less massive than M87, it appears Remarkably similar. .

This wide-field view shows rich star clouds in the constellation Sagittarius (the Archer) toward the center of our Milky Way Galaxy. The entire image is filled with huge numbers of stars, but many of them remain hidden behind dust clouds and are only revealed in infrared images. This view was created from red and blue light photographs and forms part of the Digital Sky Survey 2. The field of view is approximately 3.5° x 3.6°. Credit: ESO and Digitized Sky Survey 2. Acknowledgments: Davide De Martin and S. Guisard

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This wide-field view shows rich star clouds in the constellation Sagittarius (the Archer) toward the center of our Milky Way Galaxy. The entire image is filled with huge numbers of stars, but many of them remain hidden behind dust clouds and are only revealed in infrared images. This view was created from red and blue light photographs and forms part of the Digital Sky Survey 2. The field of view is approximately 3.5° x 3.6°. Credit: ESO and Digitized Sky Survey 2. Acknowledgments: Davide De Martin and S. Guisard

This made scientists wonder if the two shared common traits outside of their appearance. To find out, the team decided to study Sagittarius A* in polarized light. Previous studies of light around M87* revealed that magnetic fields around the giant black hole allowed it to shoot powerful jets of material back into the surrounding environment. Building on this work, new images reveal that the same may be true for Sagittarius A*.

“What we're seeing now is that there are strong, twisted, organized magnetic fields near the black hole at the center of the Milky Way,” said Sarah Isson, Einstein's fellow in NASA's Hubble Fellowship Program. ) is an astrophysicist and co-leader of the project.

“Besides that Sgr A* has a polarization structure strikingly similar to that seen in the larger and more powerful black hole M87*, we have learned that strong, ordered magnetic fields are essential to how black holes interact with the gas and matter surrounding them.”

On the left, the supermassive black hole at the center of the Milky Way, Sagittarius A*, is seen in polarized light, visible lines indicating the direction of polarization, associated with the magnetic field around the black hole's shadow. At the centre, polarized emission from the center of the Milky Way, as captured by SOFIA. In the back right, the Planck Foundation has mapped the polarized emissions from dust across the Milky Way. Image source: S. Isson, EHT Foundation

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On the left, the supermassive black hole at the center of the Milky Way, Sagittarius A*, is seen in polarized light, visible lines indicating the direction of polarization, associated with the magnetic field around the black hole's shadow. At the centre, polarized emission from the center of the Milky Way, as captured by SOFIA. In the back right, the Planck Foundation has mapped the polarized emissions from dust across the Milky Way. Image source: S. Isson, EHT Foundation

Light is an oscillating or moving electromagnetic wave that allows us to see objects. Sometimes, light oscillates in a preferred direction, which we call “polarized.” Although polarized light surrounds us, it is indistinguishable to the human eye from “normal” light.

In the plasma surrounding these black holes, particles orbiting around magnetic field lines impart a polarization pattern perpendicular to the field. This allows astronomers to see clearer details of what is happening in the black hole's regions and map out their magnetic field lines.

“By imaging polarized light from hot, glowing gas near black holes, we directly infer the structure and strength of the magnetic fields that connect the flow of gas and matter that the black hole feeds on and spews out,” said the Harvard Black Hole Initiative Fellow. Project participant Angelo Ricarte. “Polarized light teaches us a lot about astrophysics, the properties of gas, and the mechanisms that occur when a black hole feeds.”

But photographing black holes in polarized light isn't as easy as wearing a pair of polarized sunglasses, and that's especially true of Sgr A*, which changes so rapidly that it doesn't stay still when taking pictures. Imaging the supermassive black hole requires sophisticated instruments beyond those previously used to capture M87*, a much more stable target.

“It is exciting that we have been able to make a polarized image of Sagittarius A* at all. The first image took months of intense analysis to understand its dynamic nature and reveal its mesostructure,” said SAO postdoctoral fellow and astrophysicist Paul Tiede.

“Making a polarized image increases the challenge of the dynamics of the magnetic fields around the black hole. Our models often predicted highly turbulent magnetic fields, which makes it very difficult to create a polarized image. Fortunately, our black hole is much quieter, making the first image possible.” “

Scientists are excited to obtain images of both supermassive black holes in polarized light, because these images and the data that come with them provide new ways to compare and contrast black holes of different sizes and masses. As technology improves, images are likely to reveal more of the secrets, similarities and differences between black holes.

This side-by-side image of the supermassive black holes M87* and Sagittarius A*, seen here in polarized light, shows scientists that these monsters have similar magnetic field structures. This is important because it suggests that the physical processes governing how a black hole feeds and fires jets may be universal features among supermassive black holes. Credit: EHT Collaboration

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This side-by-side image of the supermassive black holes M87* and Sagittarius A*, seen here in polarized light, shows scientists that these monsters have similar magnetic field structures. This is important because it suggests that the physical processes governing how a black hole feeds and fires jets may be universal features among supermassive black holes. Credit: EHT Collaboration

“M87* and Sgr A* are different in some important ways: M87* is much larger, and it pulls matter from its surroundings at a much faster rate,” said Michie Bobock, a postdoctoral researcher at the University of Illinois Urbana-Champaign. “So, we might have expected the magnetic fields to also look very different. But in this case, they turned out to be quite similar, which could mean that this structure is common to all black holes.”

“Better understanding the magnetic fields near black holes helps us answer many open questions, from how jets form and are fired to what fuels the bright flares we see in infrared and X-rays.”

The EHT has made several observations since 2017, and is scheduled to observe Sagittarius A* again in April 2024. Each year, the images improve as the EHT incorporates new telescopes, greater bandwidth, and new observing frequencies. Expansions planned for the next decade will enable high-resolution movies of Sagittarius A*, may reveal hidden jets, and may allow astronomers to observe similar polarization features 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 key initiatives to sharply enhance EHT over the next decade. the Next generation EHT (ngEHT) A transformative EHT upgrade project is underway, with the goal of bringing multiple new radio dishes online, enabling simultaneous multi-color observations, and increasing the overall sensitivity of the array.

Expanding the ngEHT array will enable real-time movies of supermassive black holes on event horizon scales. These films will resolve the detailed structure and dynamics near the event horizon, focusing on the “strong field” gravitational features predicted by general relativity, as well as the interplay between accretion and the release of relativistic jets that sculpt large-scale structures in the universe.

at the same time, Black hole explorer The BHEX mission concept will extend the EHT into space, producing the sharpest images in the history of astronomy. BHEX will enable the detection and imaging of a “photon ring” – a sharp ring feature formed by powerful lensing emission around black holes.

Black hole properties are imprinted on the size and shape of the photon ring, revealing the masses and spins of dozens of black holes, and in turn showing how these exotic objects grow and interact with their host galaxies.

more information:
Issaoun, S. et al, First Event Horizon Telescope results from Sagittarius A*. Seventh. ring polarization, Astrophysical Journal Letters (2024), doi: 10.3847/2041-8213/ad2df0

Ricarte A. et al, “Results of the first Sagittarius A* event horizon telescope. VIII. Physical interpretation of the polarized ring,” Astrophysical Journal Letters (2024), doi: 10.3847/2041-8213/ad2df1

Magazine information:
Astrophysical Journal Letters


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