Outreach

The magnetic fields of the black hole in M87, revealed in a new light

The Event Horizon Telescope (EHT) collaboration has published new results describing for the first time how light from the edge of the supermassive black hole M87* spirals as it escapes the black hole's intense gravity. This phenomenon is known as circular polarization of light. The direction in which light's electric field prefers to spin gives us valuable information about the magnetic field and the types of particles surrounding the black hole. The new paper, published today in Astrophysical Journal Letters, supports previous EHT findings that the magnetic field near the M87* black hole is strong enough to slow the fall of matter into it.

"Circular polarization was the last chapter we needed to complete the analysis of the light in the EHT's first observations of the black hole in M87, and by far it proved to be the most challenging task of all," says Andrew Chael, a researcher at the Gravity Initiative at Princeton University, who coordinated the project. "These new results provide us with certainty that the magnetic field permeates the hot gas that falls into the black hole. The pioneering EHT observations are allowing us to answer questions about how black holes consume matter and expel jets beyond their galaxies. hostesses."

In 2019, the EHT published its first image of a ring of hot plasma near the event horizon of M87*. Then, in 2021, EHT scientists released an image showing the oscillation directions of the electric fields across the image, a phenomenon known as linear polarization. This finding marked the first indication that the magnetic fields in the vicinity of the black hole were highly organized and possessed significant intensity. The new measurements of circular polarization, which describe how the electric fields of light spiral, provide even stronger evidence for the presence of these intense and ordered magnetic fields in the vicinity of the black hole.

"The signal in circular polarization is one hundred times weaker than the non-polarized data that we used to obtain the first image of a black hole," explains Ioannis Myserlis, astronomer at the Institute of Millimeter Radio Astronomy (IRAM). "Detecting this weak signal in the data was comparable to trying to listen to a conversation over the deafening noise of a jackhammer. We had to carefully test our methods to determine what we could really trust."

This computer simulation depicts a plasma disk surrounding the supermassive black hole located at the core of the M87 galaxy. A recent analysis of circular, or spiral, polarized light in Event Horizon Telescope (EHT) observations reveals that the magnetic fields in the vicinity of the black hole exhibit remarkable intensity. These magnetic fields play a crucial role in slowing the flow of matter towards the black hole and promoting the formation of jets of matter that travel at speeds close to the speed of light. Image credit: George Wong.

To carry out this detailed analysis, the team of astronomers developed new methods to reconstruct a polarized image from the limited and noisy measurements provided by the EHT. These methods were subjected to extensive testing. "It was essential to contrast our different analysis methods with simulated data and with each other," explains Freek Roelofs, a postdoctoral researcher at the Harvard Center for Astrophysics and the Smithsonian. In a companion paper, also published today, Roelofs discovered that when he imposed very strict assumptions on his analysis, the data revealed a striking difference in the light spinning left and right in the observed ring. However, other methods that posed less restrictive hypotheses did not appreciate this difference. "Working together as a team to see what we can and can't extract from our data has made this project incredibly exciting and rewarding," says Roelofs.

The team carried out several tests on the data, all of which found conclusive evidence of the existence of circularly polarized light in the vicinity of the event horizon. In the end, because the EHT's circular polarization measurements were much weaker than those in previous data sets, the team was unable to obtain an unambiguous picture of the "orientation" of the spiraling light. However, astronomers were able to determine that the part of the light with circular or spiral polarization represented only a small fraction of the total light that made up the black hole image.

The team applied these measurements to test different theories about the shape and motion of the plasma and magnetic field around the black hole, including a set of simulations on state-of-the-art supercomputers. "The observations of circular polarization reinforce our previous results, which indicated that the magnetic fields are intense enough to slow down the fall of matter and thus launch the strong jets of plasma that we see spreading throughout the galaxy M87," says Angelo Ricarte , postdoctoral researcher at Harvard University's Black Hole Initiative. Abhishek Joshi, a graduate student at the University of Illinois, adds: "It's wonderful to directly compare our simulations with these cutting-edge observations. Together, they paint a chaotic and violent environment just outside the event horizon, where magnetic fields, gravity, and hot plasma entangle each other."

Although the current EHT data is not sensitive enough to determine the structure of the black hole's circular polarization, the team is hopeful for the near future. Ongoing analysis of new data collected after 2017 promises improvement in detecting this signal. This could provide us with information about whether matter-antimatter particle pairs are part of the plasma outside the event horizon and how they accelerate to speeds close to the speed of light.

"Working with these pioneering observations was challenging, but it prepared us for the future," says Svetlana Jorstad, a researcher at Boston University. "The EHT is growing rapidly, with new telescopes and better technology across our network, giving us a more sensitive and detailed data set to work with. It's exciting to see how much our results will improve in a short time. "

More information

More than 300 researchers from Africa, Asia, Europe, and North and South America participate in the EHT collaboration. The international collaboration is working to capture the most detailed images of black holes ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT combines existing telescopes using new techniques, creating a fundamentally new instrument with the highest angular resolving power yet achieved.

The individual telescopes participating 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 EHT consortium is made up of 13 interested institutes: the Institute of Astronomy and Astrophysics of the Academia Sinica, the University of Arizona, the University of Chicago, the East Asian Observatory, the Goethe University Frankfurt, the Institute for Millimeter Radio Astronomy, the Alfonso Serrano 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 in Nijmegen, and the Smithsonian Astrophysical Observatory.

Contact information

Andrew Chael

Princeton University

Princeton, NJ, USA

Email: achael@princeton.edu

 

Svetlana Jorstad

Boston University

Boston, MA, USA

Email: jorstad@bu.edu

 

Abhishek Joshi

University of Illinois

Champaign, IL, USA

Email: avjoshi2@illinois.edu

 

Ioannis Myserlis

Institute of Millimetric Radio Astronomy (IRAM)

Granada, Spain

Email: imyserlis@iram.es

 

Angelo Ricarte

Harvard University

Cambridge, MA, USA

Email: angelo.ricarte@cfa.harvard.edu

 

Freek Roelofs

Astrophysics Center | Harvard & Smithsonian

Cambridge, MA, USA

Email: freek.roelofs@cfa.harvard.edu

 

Geoffrey C. Bower
EHT Project Scientist
Academia Sinica Institute of Astronomy and Astrophysics
Hilo, HI, USA
Tel: +1 (510) 847-1722 (mobile)
Email:gbower@asiaa.sinica.edu.tw

Mariafelicia de Laurentis

EHT Deputy Project Scientist

University of Naples Frederick II

Naples, Italy

Email: mariafelicia.delaurentis@unina.it

Local Contact

David H. Hughes
Large Millimeter Telescope/INAOE
Tonantzintla, Puebla, Mexico
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Arturo Gomez Ruiz
Large Millimeter Telescope/INAOE
Tonantzintla, Puebla, Mexico
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David Sánchez Argüelles
Large Millimeter Telescope/INAOE
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Email: domars@inaoep.mx