A new image from the Event Horizon Telescope (EHT) array has captured the swirling magnetic fields around the supermassive black hole at the center of our galaxy, Sagittarius A (Sgr A*). This is the first time we’ve seen these fields in detail.
Surprisingly, the magnetic fields around our galaxy’s black hole look a lot like those around another giant black hole, M87*, located in a different galaxy. This similarity suggests that strong magnetic fields might be a common feature of all black holes. The new findings also hint that Sgr A* might be hiding a powerful jet of material, just like M87*.
Scientists first captured an image of Sgr A* in 2022. It’s a monster lurking 27,000 light-years away, much smaller than M87*, but with an oddly similar appearance. This led scientists to wonder if they shared other features besides looks. To investigate, they used a special kind of light to study Sgr A*. In M87*, scientists had previously discovered that magnetic fields were responsible for launching powerful jets. The new image suggests Sgr A* might have a hidden jet as well!
“What we’re seeing now is that there are strong, twisted, and organized magnetic fields near the black hole at the center of the Milky Way galaxy,” said Sara Issaoun. She is a NASA Hubble Fellowship Program Einstein Fellow at the Center for Astrophysics and Harvard & Smithsonian and co-lead of the project.
“Along with Sgr A* having a strikingly similar polarization structure to that seen in the much larger and more powerful M8*7 black hole, we’ve learned that strong and ordered magnetic fields are critical to how black holes interact with the gas and matter around them.”
Image Credit: EHT Collaboration
How did scientists capture the images?
This exciting discovery was possible thanks for polarized light. Normally, light travels in all sorts of directions, like ripples on a pond. But sometimes, light acts more like a train, only moving in one direction. This special kind of light is called “polarized.” We can’t tell the difference between regular light and polarized light with our eyes, but it’s all around us.
Near giant black holes, there’s scorching gas swirling in intense magnetic fields. These swirling particles actually cause the light coming from that gas to become polarized in a specific way. By studying this polarized light, scientists can see the black hole region in much greater detail. It’s like having special glasses that reveal the hidden magnetic fields, swirling around the black hole like threads.
“By imaging polarized light from hot glowing gas near black holes, we are directly inferring the structure and strength of the magnetic fields that thread the flow of gas and matter that the black hole feeds on and ejects,” said Harvard Black Hole Initiative Fellow and project co-lead Angelo Ricarte. “Polarized light teaches us a lot more about the astrophysics, the properties of the gas, and mechanisms that take place as a black hole feeds.”
The challenges
The problem in capturing Sgr A* was that it’s changing so fast that it doesn’t sit still for pictures. Imaging the supermassive black hole requires advanced tools beyond those used for capturing M87*. EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan, said:
“Making a polarized image is like opening the book after you have only seen the cover. Because Sgr A* moves around while we try to take its picture, it was difficult to construct even the unpolarized image,” adding that the first image was an average of multiple images due to Sgr A*’s movement. “We were relieved that polarized imaging was even possible. Some models were far too scrambled and turbulent to construct a polarized image, but nature was not so cruel.”
At left, the supermassive black hole at the center of the Milky Way Galaxy, Sagittarius A*, is seen in polarized light, the visible lines indicating the orientation of polarization, which is related to the magnetic field around the shadow of the black hole. At center, the polarized emission from the center of the Milky Way, as captured by SOFIA. At back right, the Planck Collaboration mapped polarized emission from dust across the Milky Way. Image Credit: S. Issaoun, EHT Collaboration
The scientific importance of the new supermassive black hole images
Researchers are excited to have captured images of both supermassive black holes in polarized light. These images, along with the data they provide, give new opportunities to compare and contrast black holes of different sizes and masses. With the continuous advancements in technology, these images are expected to reveal more secrets about the similarities and differences of black holes.
Mariafelicia De Laurentis, EHT Deputy Project Scientist and professor at the University of Naples Federico II, Italy, said:
“The fact that the magnetic field structure of M87* is so similar to that of Sgr A* is significant because it suggests that the physical processes that govern how a black hole feeds and launches a jet might be universal among supermassive black holes, despite differences in mass, size, and surrounding environment. This result allows us to refine our theoretical models and simulations, improving our understanding of how matter is influenced near the event horizon of a black hole.”
Future plans
The Event Horizon Telescope (EHT) has been observing the black hole, Sagittarius A* (Sgr A*), since 2017, with multiple observations planned. The next observation of Sgr A* is scheduled for April 2024. Every year, the EHT incorporates new telescopes, larger bandwidth, and new observing frequencies, resulting in improved images. Not long from now, we’ll have even sharper images of black holes than ever before!
[via Space.com; lead image credit: EHT Collaboration]
