Humanity’s quest to capture images of black holes has reached a milestone as a telescope array recently recorded the swirling magnetic fields surrounding two of the nearest supermassive black holes to Earth.
For the first time, these magnetic fields have been observed in polarized light, providing a new perspective on Sgr A*, the black hole at the center of our Milky Way Galaxy. The magnetic field structure of Sgr A* bears a striking resemblance to that of the black hole in the center of the Messier 87 galaxy, indicating that robust magnetic fields might be a common feature among all black holes.
This similarity also suggests the presence of a concealed jet in Sgr A*. The findings, published in The Astrophysical Journal Letters, shed light on this phenomenon.
In 2022, scientists unveiled the first image of Sagittarius A*, located approximately 27,000 light-years away from Earth. Despite being significantly smaller and less massive than the black hole in Messier 87, Sgr A* displayed surprising similarities in appearance. This led researchers to wonder if the two black holes shared common characteristics beyond their visual resemblance.
To explore this further, the team examined Sgr A* in polarized light. Previous studies of the light around the black hole in Messier 87 revealed that its magnetic fields enabled it to emit powerful jets of material into its surroundings. Building on this knowledge, the new observations suggest that Sgr A* may also possess such jets, further deepening our understanding of these enigmatic cosmic phenomena.
“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,” Sara Issaoun, NASA Hubble Fellowship Program from Harvard and the Smithsonian who co-led the project, shared.
“Along with Sgr A* having a strikingly similar polarization structure to that seen in the much larger and more powerful M87* 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.”
Light is a dynamic force, pulsating as an electromagnetic wave, enabling our vision of the world around us. Sometimes, this light moves with a preferred alignment, a phenomenon known as polarization. While polarized light is ubiquitous, to the human eye it appears no different from unpolarized light. However, in the plasma surrounding black holes, particles swirling along magnetic field lines create a distinct polarization pattern perpendicular to the field.
This unique characteristic enables astronomers to delve into the depths of black hole regions with greater clarity, offering vivid insights into their dynamics and allowing for the mapping of their magnetic field lines.
“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,” Angelo Ricarte, Harvard Black Hole Initiative Fellow and project co-lead said. “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.”
Imaging the supermassive black hole requires advanced tools beyond those previously used for capturing M87*, which is a much steadier target.
“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,” said Geoffrey Bower, EHT Project Scientist. “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.”
The images of Sgr A* are formed by combining multiple observations. The Event Horizon Telescope (EHT) has been conducting observations of Sgr A* since 2017 and is set to observe it again in April 2024. With each passing year, the quality of these images has been on the rise. This improvement is attributed to the EHT’s integration of new telescopes, wider bandwidth, and utilization of different observing frequencies.
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