The Event Horizon Telescope (EHT) collaboration, which includes Iván Martí Vidal, researcher at the Astronomical Observatory of the University of Valencia Science Park (PCUV), has presented the first polarized light image of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way. This image reveals the presence of intense and organized magnetic fields that emerge in a spiral shape from the very edge of the black hole
The Event Horizon Telescope (EHT) collaboration has released the first polarized light image of SgrA*, the supermassive black hole at the center of our galaxy. This image reveals the presence of intense and organized magnetic fields that emerge in a spiral shape from the very edge of the black hole.
This structure is similar to that observed in the central black hole of the galaxy M87, suggesting that these intense magnetic fields may be common to all black holes and pointing to the possible existence of a hidden jet in Sgr A*, like the one in M87*. These results were published Wednesday in The Astrophysical Journal Letters.
In May 2022 the Event Horizon Telescope (EHT) collaboration presented the first image of Sgr A*, the supermassive black hole at the center of our galaxy, about 27 000 light-years from Earth. That image looked surprisingly similar to the black hole in the galaxy M87, despite being more than a thousand times smaller and less massive than the latter. Now, the EHT has just released the polarized version of the SgrA* image. Previous studies of M87* in this type of light had confirmed the presence of intense and organized magnetic fields, associated with the emission of powerful jets of material at near-light speeds. Based on this work, the new images of SgrA* have revealed that the same may be occurring in the center of our galaxy.
"What we are now observing is the presence of intense, twisted, organized magnetic fields near the black hole at the center of the Milky Way," says Sara Issaoun, a NASA Einstein Hubble Fellowship Program researcher at the Astrophysics Center/Harvard and Smithsonian, and co-leader of the project. "The fact that Sgr A* exhibits a polarization structure strikingly similar to that of a much larger and more powerful black hole such as M87* has allowed us to deduce that intense and organized magnetic fields play a key role in the interaction of black holes with the gas and matter around them," she added.
"We have had to develop pioneering algorithms to recover the faint polarized signal from these black holes. From the University of Valencia, we have provided fundamental calibration data for the analysis of these observations; data that have also helped us to detect the polarized reflection of matter orbiting the black hole," Iván Martí Vidal, professor in the Department of Astronomy and Astrophysics at the University of Valencia and member of the EHT
Polarized light traces magnetic fields
Light is an electromagnetic wave that sometimes oscillates in a preferred direction. This is when we speak of "polarized light". Although this type of light is commonplace in our daily lives (from polarized sunglasses or cameras to 3D cinema systems), to human eyes it is indistinguishable from non-polarized light. When there is a strong magnetic field, the plasma particles surrounding black holes emit radiation with a polarization pattern perpendicular to the field. This makes it possible to reconstruct the magnetic structure in these regions and to observe in detail what is happening in the vicinity of black holes.
"Polarized light imaging of hot glowing gas near black holes allows us to directly deduce the structure and intensity of the magnetic fields that pass through the flow of gas and matter that feeds the black hole, as well as that which it ejects," says Angelo Ricarte, a researcher at Harvard University's Black Hole Initiative Institute, and co-leader of the project. "Polarized light offers us valuable insights into astrophysics, the properties of the gas, and the mechanisms that occur as a black hole feeds."
Dynamic changing black hole
But imaging black holes with polarized light is not as easy as putting on polarized sunglasses. The technology behind it has been decades in the making, and finally, in this decade, we are beginning to reap its rewards. "We have had to develop pioneering algorithms to recover the faint polarized signal from these black holes. From the University of Valencia, we have provided fundamental calibration data for the analysis of these observations; data that have also helped us to detect the polarized reflection of matter orbiting the black hole," says Iván Martí Vidal, professor in the Department of Astronomy and Astrophysics at the University of Valencia and member of the EHT.
Universal black holes
Having images and data of both supermassive black holes in unpolarized light opens up new opportunities to compare and contrast black holes of different sizes and masses. As technology advances, these images are likely to reveal even more secrets about the black holes and their possible similarities or differences.
"We have long been looking for the possible jet of matter emanating from our galactic center. This new polarized image tells us that the jet should be there, but we don't see it yet. It is an intriguing question that remains to be clarified," says Alejandro Mus, PhD in Physics from the University of Valencia and member of the EHT.
The EHT has conducted several observations since 2017 and is scheduled to observe Sgr A* again in April 2024. Each year, the images improve as the EHT adds new telescopes, increased bandwidth, and new observing frequencies. Expansions planned for the next decade will provide highly reliable movies of Sgr A*, which could reveal the presence of a hidden jet and allow astronomers to observe similar polarization features in other black holes. In the meantime, extending the EHT into space will provide sharper images of black holes than ever before.
"We have long been looking for the possible jet of matter emanating from our galactic center. This new polarized image tells us that the jet should be there, but we don't see it yet. It is an intriguing question that remains to be clarified," Alejandro Mus, PhD in Physics from the University of Valencia and member of the EHT
300 researchers
The EHT collaboration involves more than 300 researchers from Africa, Asia, Europe, and North and South America. This international effort aims to capture images of black holes at an unprecedented level of detail by creating a virtual telescope the size of the Earth. Backed by considerable international investment, the EHT connects existing telescopes through innovative systems, resulting in a completely new instrument with the highest angular resolving power ever achieved.
The telescopes involved in the EHT are ALMA, APEX, the IRAM 30-meter Telescope, the IRAM NOEMA Observatory, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), the South Pole Telescope (SPT), the Kitt Peak Telescope, and the Greenland Telescope (GLT). The data were correlated at the Max-Planck-Institut für Radioastronomie (MPIfR) and the MIT Haystack Observatory. The post-processing was performed within the collaboration by an international team at different institutions, with a very prominent participation of the Institute of Astrophysics of Andalusia (CSIC).
The EHT consortium includes thirteen interested institutions, in addition to many other research institutes around the world, including the IAA-CSIC: Academia Sinica Institute for Astronomy and Astrophysics, the University of Arizona, the University of Chicago, the East Asia Observatory, Goethe University Frankfurt, the Institute for Millimeter Radio Astronomy, the Large Millimeter Telescope, the Max Planck Institute for Radio Astronomy, the MIT Haystack Observatory, the National Astronomical Observatory of Japan, the Perimeter Institute for Theoretical Physics, Radboud University and the Smithsonian Astrophysical Observatory.
References
This research was presented in two papers by the EHT collaboration published today in The Astrophysical Journal Letters: "First Sagittarius A* Event Horizon Telescope Results. VII. Polarization of the Ring and "First Sagittarius A* Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring