2024-01-26 06:00:08
In 2019, the Event Horizon Telescope published the historic first image of a black hole: M87*, a supermassive black hole located at the center of the Messier 87 galaxy, 55 million light-years away from Earth. Thanks to combined observations throughout 2017 from a global network of radio telescopes that function as a virtual Earth-sized telescope, an image of a bright circular ring was obtained, brighter in its southern part. Subsequent analyzes of its structure in polarized light allowed us to determine the geometry of the magnetic field and the nature of the plasma surrounding the black hole.
Scientists have now presented a new image of M87*, based on the analysis of observations made in April 2018. These observations, which include the participation of the Greenland Telescope for the first time in the global Event Horizon Telescope network, provide a set of data independent of those captured in 2017.
The Event Horizon Telescope (EHT) is an international project with strong participation from the Institute of Astrophysics of Andalusia (IAA), dependent on the Higher Council for Scientific Research (CSIC) in Spain.
Published in the academic journal Astronomy & Astrophysics, this new analysis reveals a bright ring of dimensions identical to those observed in 2017 around a dark central region, which corresponds to the shadow cast by the black hole, in line with the predictions of the theory of general relativity. However, in this new image, the most luminous region of the ring has experienced a shift of approximately 30 degrees compared to 2017, in accordance with theoretical models that describe the variability of the turbulent material surrounding black holes.
“A fundamental requirement of science is to be able to reproduce results,” says Keiichi Asada, a research associate at the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan. “Confirmation of the ring in a completely new set of data is a huge milestone for our collaboration and a strong indication that we are observing the shadow of a black hole and the material orbiting it.”
“Obtaining the direct image of M87* marked a new stage in the study of black holes, allowing for increasingly precise verifications of the theory of general relativity based on multiple astronomical observations,” says José Luis Gómez, vice president. of the EHT Scientific Council and leader of the EHT group at the IAA, which includes doctors Kotaro Moriyama, Thalia Traianou, Antonio Fuentes and Antxon Alberdi, as well as predoctoral researchers Rohan Dahale, Marianna Foschi and Teresa Toscano, and former members Ilje Cho, Rocco Lico, and Guang-Yao Zhao. “Our theoretical models ensure that the properties of the material surrounding M87* should be uncorrelated between 2017 and 2018. Therefore, continued observations of M87* will help us establish independent constraints on the structure of the plasma and the magnetic field around it.” of the black hole, and will allow us to distinguish complex astrophysics from the effects of general relativity,” adds Gómez
To contribute to this exciting new science, the EHT is in constant development. The Greenland Telescope first joined the EHT in 2018, just five months after its construction in the Arctic Circle was completed. Likewise, the LMT (Large Millimeter Telescope) radio telescope participated for the first time with its total surface area of 50 meters, considerably improving its sensitivity. In addition, observations were expanded to four frequency bands around 230 GHz, compared to the two bands used in 2017.
“The advancement of science implies a constant improvement in the quality of data and analysis techniques,” highlights Rohan Dahale, a predoctoral researcher at the IAA, who has contributed essentially to the new EHT results. “The integration of the Greenland Telescope into the EHT network has been essential in refining our images of M87* in 2018. For observations carried out in 2021, 2022 and the next ones in 2024, other significant improvements have also been implemented that inspire us to continue expanding the boundaries in black hole astrophysics.”
Comparison of the images of the M87 black hole, in 2017 and 2018. (Photos: EHT)
Consistency with general relativity
The image of M87* taken in 2018 is remarkably similar to the one from 2017: a bright ring of identical size and width, with a dark central region and one side of the ring brighter than the other. Precisely, one of the most notable results of this new image of M87* is the stability of the diameter of its ring with respect to the 2017 data, which strongly supports the conclusion that the M87 black hole is well described by the theory of general relativity. “The radius of a black hole only depends on its mass. Since M87* is not accreting material (which would increase its mass) at a high rate, general relativity predicts that its radius should remain practically unchanged on human time scales, as confirmed by our data,” says Nitika Yadlapalli Yurk, postdoctoral researcher at the Jet Propulsion Laboratory in California (USA), and doctor from the California Institute of Technology.
Although the size of the black hole’s shadow has remained constant between 2017 and 2018, the position of the ring’s brightest region has undergone a significant change in the new 2018 data, moving about 30 degrees counterclockwise to be located in the bottom right of the ring, approximately at the five o’clock position. “This notable change in the structure of M87* is something we already anticipated in the first results published in April 2019” – explains Britt Jeter, postdoctoral researcher at the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan – Although the theory Since general relativity requires that the size of the ring must remain stable, emission from the chaotic and turbulent accretion disk surrounding the black hole causes the brightest region of the ring to oscillate from side to side. “The observed amplitude of this oscillation or wobble over time will serve to test our theories about the magnetic field and the plasma environment around the black hole.”
New analysis tools
The analysis of the 2018 data incorporates eight independent imaging and modeling techniques, including both methods used in the previous analysis of M87* in 2017 and new ones developed from the experience gained from the analysis of Sgr A*, the black hole located in the center of the Milky Way.
“The robustness of the image obtained is significantly strengthened thanks to the diversity of image reconstruction and modeling techniques used. The consistency in image morphology, demonstrated by the five mapping and three modeling methods, significantly reinforces the reliability of our results,” says Kotaro Moriyama, one of the coordinators of the EHT Image Working Group. “It is especially It is notable that members of the IAA have provided key contributions to this milestone, leading or co-leading the imaging processes with four of the five different imaging techniques,” adds Moriyama.
A project in continuous expansion
In addition to 2017 and 2018, the EHT has carried out observations of M87* in 2021 and 2022, and is scheduled to observe in the first half of 2024. Each year, the EHT network has improved technically, either with the addition of new telescopes, hardware improvements or adding additional observing frequencies. “The observations made by the EHT imply a substantial contribution to the understanding of the physics of black holes. The expansion of the EHT will improve the quality of the images. In this sense, the IAA and other partners are studying the possible incorporation into the network of a new radio antenna in the Canary Islands. Research with the EHT is a fundamental part of the Severo Ochoa strategic project of the IAA”, highlights Antxon Alberdi, member of the EHT Collaboration and director of the IAA.
The EHT collaboration includes the participation of more than 300 researchers from Africa, Asia, Europe, and North and South America. This international effort aims to capture images of black holes in an unprecedented level of detail, by creating a virtual Earth-sized telescope. Backed by considerable international investment, the EHT connects existing telescopes using 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 at MIT’s Haystack Observatory. The subsequent processing was carried out within the collaboration of an international team in different institutions, with a very prominent participation from the Institute of Astrophysics of Andalusia. (Source: Emilio García / IAA / CSIC)
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