New Even Horizon Telescope Results Trace M87 Jet Back to Its Black Hole

A Hubble Space Telescope image of the giant elliptical galaxy M87 with its blowtorch-like jet. The visible part of this giant stream of particles spans around 3000 light-years. © NASA, ESA, A. Lessing (Stanford University), E. Baltz (Stanford University), M. Shara (AMNH), J. DePasquale (STScI)

At 230 GHz (bottom), data from the EHT reveal the fine structure of the ring surrounding the supermassive black. © Bottom: Saurabh et al.: “Probing jet base emission of M87* with the 2021 Event Horizon Telescope observations”, Astronomy & Astrophysics 705 (2026), Figure 6. Upper Right: Lu, R.-S. et al.: “A ring-like accretion structure in M87 connecting its black hole and jet”. Nature 616 (2023), Figure 1

Selected sites from the 2021 EHT observing campaign, highlighting additional stations: the 12−m Kitt Peak (KP) Telescope, USA and the NOrthern Extended Millimeter Array (NOEMA), France. This introduces two critical intermediate-length baselines to the Submillimeter Telescope (SMT), USA and IRAM 30−m, Spain, providing sensitivity to emission structures close to the base of the jet. © Saurabh/MPIfR

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To the point:

• Recently published data from the Event Horizon Telescope (EHT) of the galaxy Messier 87 facilitate new insights into the direct environment of the central supermassive black hole.

• Measured differences in the radio light on different spatial scales can be explained by the presence of an as of yet undetected jet at frequencies of 230 Gigahertz at spatial scales comparable to the size of the black hole.

• The most likely location of the jet base is determined through detailed modeling.

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Observations with the Event Horizon Telescope enable researchers to localize the likely base of the central outflow in a massive galaxy

Some galaxies eject powerful streams of charged particles—jets—from their centers into space. The prominent jet of Messier 87 (M87) in the constellation Virgo is visible over distances of 3000 light-years and can be observed over the full electromagnetic spectrum. It is powered by the central engine, the supermassive black hole at the heart of the galaxy with a mass of around six billion times that of our Sun. The exact location around the black hole where the jets originate is still unknown. Using observations from the Event Horizon Telescope (EHT) from 2021, an international research team led by Saurabh (Max Planck Institute for Radio Astronomy, MPIfR), Hendrik Müller (National Radio Astronomy Observatory, NRAO) and Sebastiano von Fellenberg (formerly at MPIfR, currently at the Canadian Institute for Theoretical Astrophysics, CITA) has found first hints of the jet base in M87. The results are published in the current issue of the journal Astronomy & Astrophysics.

Observing different scales

M87*, the supermassive black hole at the center of the galaxy M87, is about 55 million light years (5 × 10²⁰ kilometers) away from Earth. In 2019, the first images of its shadow and the glowing ring of hot gas around it went around the world. In order to resolve these structures, radio telescopes around the world must be combined into a single virtual telescope such as the EHT. This technique is called Very Long Baseline Interferometry (VLBI). The images produced in this way are sensitive to emission on different scales, depending on the distances between telescopes (baselines): With long baselines of several thousand kilometers, the smallest structures—such as the luminous ring—around M87* can be depicted. Short baselines of a few hundred meters, on the other hand, reveal emission emanating from much larger spatial scales in M87 (the extended jet), but are blind to details near the black hole. Intermediate baselines of a few hundred to a few thousand kilometers are the important link. They can be used to establish a connection between the material around the black hole and the jet. Precisely these intermediate baselines enabled the research team to determine the probable position of the jet base. "This study represents an early step toward connecting theoretical ideas about jet launching with direct observations. Identifying where the jet may originate and how it connects to the black hole’s shadow, adds a key piece to the puzzle and points toward a better understanding of how the central engine operates", explains Saurabh.

The decisive difference

The researchers find hints to the base of the jet by comparing the measured radio intensity on different spatial scales: On short to intermediate baselines, the measured intensity is higher compared to that on long baselines. This indicates that what is observed with long baselines—the luminous ring of hot gas around the black hole—is not solely responsible for the detected radio emission. Instead, the current data show that part of the missing emission is captured on intermediate baselines. One possibility is the jet, which has not yet been observed at a radio frequency of 230 gigahertz (GHz) with the EHT.

EHT observations from 2017 and 2018 lacked the intermediate baselines to detect it. However, with the recently published data, Saurabh's team was able to show with numerous model calculations that part of the missing emission can be best explained by an additional compact region. From our perspective, this region is about 0.09 light-years away from M87* and associated with the base of the jet. The position of the region appears to coincide with the southern arm of a radio jet discovered at a different frequency (86 GHz) in 2018. "We have observed the inner part of the jet of M87 with global VLBI experiments for many years, with ever increasing resolution, and finally managed to resolve the black hole shadow in 2019. It is amazing to see that we are gradually moving towards combining these breakthrough observations across multiple frequencies and complete the picture of the jet launching region", says Hendrik Müller.

What’s next?

The current study shows that these interesting structures around M87* become visible at radio frequencies of 230 GHz with intermediate baselines. However, further observations with the EHT will be necessary to further constrain the morphology of the jet. These observations will then make it possible to not only deduce structures such as the jet base, but to image them. This opens up new possibilities for probing the direct environment of supermassive black holes and for testing theories of black hole physics. "Newly observed data—now being correlated and calibrated with support from MPIfR—will soon add back the Large Millimetre Telescope in Mexico. This will bring an even sharper view of the jet‑launching region within reach", says Sebastiano von Fellenberg.

Source: Max Planck for Radio Astronomy/Press Releases

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Additional Information

The following scientists affiliated to the MPIfR are coauthors of this publication: Saurabh, Sebastiano D. von Fellenberg, Michael Janssen, Thomas P. Krichbaum, Dhanya G. Nair, Walter Alef, Rebecca Azulay, Uwe Bach, Anne-Kathrin Baczko, Silke Britzen, Gregory Desvignes, Sergio A. Dzib, Ralph P. Eatough, Christian M. Fromm, Ramesh Karuppusamy, Joana A. Kramer, Michael Kramer, Jun Liu, Andrei P. Lobanov, Ru-Sen Lu, Nicholas R. MacDonald, Nicola Marchili, Karl M. Menten, Cornelia Müller, Georgios Filippos Paraschos, Alexander Plavin, Eduardo Ros, Helge Rottmann, Alan L. Roy, Tuomas Savolainen, Lijing Shao, Pablo Torne, Efthalia Traianou, Jan Wagner, Robert Wharton, Gunther Witzel, Jompoj Wongphexhauxsorn, J. Anton Zensus, and Guang-Yao Zhao.

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Contacts:

Mr. Saurabh
Tel: +49 228 525-366
saurabh@mpifr-bonn.mpg.de
Max Planck Institute for Radio Astronomy, Bonn

Dr. Hendrick Müller
Tel: +1 626 781-0043
hmuller@nrao.edu
National Radio Astronomy Observatory (NRAO), USA

Dr. Sebastiano von Fellenberg
Tel: +1 437 328-5547
sfellenberg@utoronto.ca
Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto, Canada

Dr. Nina Brinkmann
Press and Public Relations
Tel: +49 228 525-399
brinkmann@mpifr-bonn.mpg.de
Max Planck Institute for Radio Astronomy, Bonn

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Original publication

Saurabh et al.
Probing jet base emission of M87* with the 2021 Event Horizon Telescope observations
Astronomy & Astrophysics 705 (2026)
[doi.org/10.1051/0004-6361/202557022]

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Parallel Press Release

CITA Press Release
From the Canadian Institute for Theoretical Astrophysics

Saurabh/MPIfR

Animation (open in full screen)

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Images

• eht_closure_phase_triangles 1.56 MB


• m87_possible_jet_base 1.13 MB


• m87_possible_jet_base_blank 1.11 MB

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Euclid Sheds Light on How Galaxies Form and Transform

The “Morphological Tuning Fork” of galaxy classifications, re-created using Euclid’s high-resolution images from data release Q1. © ESA/Euclid/Euclid Consortium/NASA, diagram by J.-C. Cuillandre, L. Quilley, F. Marleau

ESA’s space telescope captures the astonishing diversity of galaxies – and MPE scientists trace how mergers shape their cores

ESA’s Euclid space telescope is revealing the patterns of galaxy evolution, capturing the shapes, sizes, and structures of millions of galaxies across cosmic time. Scientists from the Max Planck Institute for Extraterrestrial Physics (MPE) are using these data to trace how galaxies grow, merge, and transform, including identifying hundreds of systems with secondary nuclei that hint at the formation channels of supermassive black hole binaries. Euclid also uncovers rare systems with highly ionized emission lines and thousands of previously hidden dwarf galaxies, providing key insights into the building blocks of larger systems like the Milky Way. Together, these observations offer a comprehensive view of how galaxies and their central black holes coevolve across the universe.

Summary:

Euclid Telescope: ESA's Euclid space telescope captures diverse galaxy forms and structures, enhancing understanding of galaxy evolution and mergers.

Galaxy Evolution: Researchers from the Max Planck Institute for Extraterrestrial Physics (MPE) study how galaxies grow and merge, identifying systems with secondary nuclei that may host supermassive black hole binaries.

Data Insights: The first data release includes millions of galaxies, allowing astronomers to investigate connections between galaxy morphology and environmental influences.

Research Breakthroughs: Euclid’s sharp, wide-field images enable the systematic study of the central structures of galaxies and the identification of rare phenomena—including highly ionized emission lines and previously hidden dwarf galaxies—providing crucial insights into galaxy formation.

Comprehensive View: The findings illustrate the relationship between galaxy structure, star formation history, and cosmic environment, offering a holistic view of galactic evolution.

After just one year of observations, ESA’s space telescope Euclid is shedding new light on one of astronomy’s oldest questions: why does the universe contain such a stunning variety of galaxies? Just like flowers, galaxies come in a large variety of different colours, sizes, and shapes — all encapsulated in the term: morphology.

Are these different morphologies linked? How is the evolution of blue spiral galaxies related to that of giant elliptical galaxies? And how much does a galaxy’s environment — whether it lives in crowded clusters or cosmic solitude — influence its shape and fate? With millions of galaxies now catalogued in Euclid’s first data release (Q1, March 2025, ESA), astronomers are gaining access to a new treasure trove of data to address these questions.

Euclid’s sharp, wide-field view marks a breakthrough in extragalactic astronomy. Its images combine exceptional depth and resolution, allowing scientists to study more than 1.2 million large galaxies in its first year alone—and tens of millions over its six-year mission.

We understand today that the diversity of galaxies — from majestic grand-design spirals like our own Milky Way to giant ellipticals such as the mighty Messier 87 — is a consequence of their evolutionary paths. Galaxies begin their lives on the right side of the Hubble diagram (see Figure above) as disky, blue, star-forming systems. They move to the left in the diagram as they grow, gradually exhaust their gas supplies, and merge with other systems, eventually forming large elliptical galaxies.

One of the discovered systems with secondary nuclei. These are potential hosts of a second supermassive black hole that is in the process of sinking—assisted by dynamical friction—into the centre of the recently merged host galaxy. The image, in addition to the secondary nucleus, still clearly shows residual traces of the merger process. © ESA/Euclid/Euclid Consortium/MPE

A comprehensive view of cosmic evolution

Euclid’s Q1 release covers 63 square degrees of the extragalactic sky — only about 0.5% of the total dataset the mission will ultimately deliver. Yet, even this small fraction already enables a remarkable range of high-impact studies across all areas of extragalactic astronomy, demonstrating one of Euclid’s key strengths: its ability to efficiently survey vast regions of the sky and reveal rare astronomical phenomena.

Another example is the study by Daniela Vergani et al., co-led by Christoph Saulder (MPE), which identifies a rare population of 65 galaxies exhibiting highly ionised emission lines — signatures of extreme astrophysical phenomena such as active galactic nuclei, shock fronts, or Wolf–Rayet stars — offering a new window into the energetic feedback mechanisms shaping galaxy evolution.

With its remarkable sensitivity, Euclid also reveals that the most common galaxies in the Universe are not the majestic spirals but tiny dwarf galaxies—faint, low–surface-brightness systems that were once too elusive to study in detail. Among the 2,674 dwarf galaxies identified so far, about 58% are dwarf ellipticals and 42% are dwarf irregulars, some containing compact blue cores or globular clusters. These dwarfs are thought to be the building blocks of larger systems like our own Milky Way, offering vital clues to cosmic assembly on the smallest scales.

These studies — from tiny dwarfs to giant ellipticals — demonstrate Euclid’s extraordinary ability to provide a complete, multi-scale view of galaxy formation and evolution. Its data reveal the physical links between a galaxy’s structure, its star-formation history, and its cosmic environment, connecting all phases of galactic life into a single, coherent picture. Euclid is transforming our understanding of the Universe’s “tuning fork,” showing how galaxies light up with star formation, collide, and fade — and how, at their hearts, black holes and stellar cores evolve together.

Source: Max Planck Institute for Astrophysics/News

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Contacts:

Dr. Maximilian Fabricius
Leader German Science Data Center SDC-DE
Tel: +49 89 30000-3712
Fax: +49 89 30000-3569
mxhf@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

Prof. Dr. Roberto Saglia
Scientist OPINAS
Tel: +49 89 30000-3495
saglia@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

Dr. Christoph Saulder
Postdoc OPINAS
Tel: +49 89 30000-3774
csaulder@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

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Further Information

Euclid opens a treasure trove of data: MPE plays a crucial role in exploring the dark universe

March 19, 2025

The first Euclid data published by ESA (Q1) provide impressive insights into the depths of the universe. They include high-resolution images of 26 million galaxies, reveal the finest structures and make it possible for the first time to precisely determine the shape and distance of more than 380,000 galaxies. This data is a milestone and yet only marks the beginning of research into dark matter and dark energy. And the Max Planck Institute for Extraterrestrial Physics (MPE) plays a central role in all of this.

more

Zoom into the first page of Euclid’s great cosmic atlas

October 15, 2024
Euclid reveals the first deep view into the cosmos, spanning an area of 500 full moons in the sky.

more

MPE-built optical assembly fully integrated on EUCLID-NISP

December 21, 2018

Last week at LAM Marseille, the optical assembly consisting of the camera lens assembly “CaLA” and the corrector lens assembly “CoLA” have been fully integrated on the near-infrared optics NISP for the Euclid satellite. Euclid is an ESA mission, planned to launch in 2022 to study the “Dark Universe”. Scientists at the Max Planck Institute for Extraterrestrial Physics are responsible for the overall optical design of the near-infrared instrument NISP NI-OA.

more

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Braided Magnetic Flux Ropes Are Found at Both Human and Light Year Scales

Four braided structures. (a) astrophysical jet M-87, 3000 light years long; (b) Double Helix Nebula, 70 light years long; (c) solar prominence, 3000 kilometers long; (d) solar loop manufactured in Bellan lab at Caltech, 3 centimeters long. Credit: (a) Passeto et al., Sophia Dagnello, NRAO/AUI/NSF; (b) NASA/JPL-Caltech/M. Morris (UCLA); (c) High Altitude Observatory Archives; (d) Yang Zhang, Caltech Bellan Plasma Lab

Four braided structures. (a) astrophysical jet M-87, 3000 light years long; (b) Double Helix Nebula, 70 light years long; (c) solar prominence, 3000 kilometers long; (d) solar loop manufactured in Bellan lab at Caltech, 3 centimeters long. Credit: (a) Passeto et al., Sophia Dagnello, NRAO/AUI/NSF; (b) NASA/JPL-Caltech/M. Morris (UCLA); (c) High Altitude Observatory Archives; (d) Yang Zhang, Caltech Bellan Plasma Lab

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Investigating solar corona structures has led Paul Bellan, Caltech professor of applied physics, and his former graduate student Yang Zhang (PhD '24) to discover a new equilibrium state of the magnetic field and its associated plasma. The solar corona, the outermost part of the Sun's atmosphere, is much less dense than the Sun's surface but is a million times hotter. The corona is composed of strong magnetic fields confining plasma, a gaseous soup of charged particles (electrons and ions). The new equilibrium, called a double helix, applies not only to the solar corona but also to much larger astrophysical configurations such as the Double Helix Nebula located near the center of the Milky Way galaxy.

Solar corona structures such as flares often have the form of magnetic flux ropes: twisted tubes of plasma-containing magnetic fields. Such a rope can be visualized as a plasma-filled garden hose with a stripe wrapped around it in a helical pattern. An electric current flows along the length of the hose, and the helical stripe corresponds to the twisted magnetic field. Because it is charged, plasma conducts electric currents and is attached, or "frozen," into magnetic fields.

Magnetic flux ropes occur in a variety of situations ranging from the human scale—say, a laboratory experiment—to the absolutely huge: solar flares that are few hundred thousand kilometers long. Astrophysical structures with magnetic flux ropes can also span hundreds or even thousands of light-years.

In a large laboratory vacuum chamber, Bellan and Zhang (now a NASA Jack Eddy postdoctoral fellow at Princeton) produced solar flare replicas measuring between 10 and 50 centimeters long. "We have two electrodes inside the vacuum chamber, which has coils producing a magnetic field spanning the electrodes. Then we apply high voltage across the electrodes to ionize initially neutral gas to form a plasma," Yang explains. "The resulting magnetized plasma configuration automatically forms a braided structure."

This braided structure consists of two flux ropes that wrap around one another to form a double helix structure. In the experiments, this double helix was observed to be in a stable equilibrium—in other words, it holds its structure without tending to twist tighter or untwist. In a new paper, Zhang and Bellan demonstrate that the stable equilibrium of these double-helix flux ropes can be understood, analyzed, and predicted accurately in mathematical terms.

Though the properties of single flux ropes are well known, braided flux ropes were not well understood—especially those configurations in which the electric currents flow in the same direction along both of the braided strands. Scientists have modeled the other possible situation—where currents flow in one direction in one flux rope and in the opposite direction in the other—but this scenario is thought to be unlikely in nature.

The same-current configuration is especially important because it would be susceptible to kinking and expansion driven by hoop forces—phenomena observed both in braided solar structures and in laboratory experiments. Such kinking and expansion should not occur when current flows in opposite directions in the braided strands (a "no-net-current" state).

Previously, scientists assumed that braided flux ropes where the strands have current flowing in the same direction would always merge, because parallel currents magnetically attract each another. However, in 2010, researchers at Los Alamos National Laboratory found that such flux ropes instead bounce off one another as they come closer together.

"There was clearly something more complicated going on when the flux ropes are braided, and now we have shown what that is," Bellan says. "If you have electrical currents flowing along two helical wires that wrap around each other to form a braided structure, as seen in our lab, the components of the two currents flowing along the length of the two wires are parallel and attract, but the components of the two currents flowing in the wrapping direction are anti-parallel and repel. This combination of both attractive and repulsive forces means there will be a critical helical angle at which these opposing forces balance, producing an equilibrium. If the helical flux ropes twist tighter, there will be too much magnetic repulsion; if they twist more loosely, there will be too much magnetic attraction. At the critical angle of twist, the helical structure arrives at its lowest energy state, or equilibrium."

The next task was to create a mathematical model of this behavior—something not previously done. Using what Bellan describes as "brute force mathematics," Zhang created a set of equations that could apply to multiple flux tubes in various configurations, including braided ropes, and showed there is indeed a state at which the attractive and repulsive forces balance each other, creating an equilibrium. "And as an unexpected bonus, Yang can calculate the magnetic fields inside and outside the flux ropes, and the current and pressure inside them," Bellan says, "giving us a full picture of the behavior of these braided structures."

Zhang tested his mathematical model against the Double Helix Nebula, an astrophysical plasma formation located 25,000 light-years from Earth that covers a 70 light-year swath of space, to see if the equations could describe a large model as well as it did the structures he and Bellan created in the lab. "What was rather amazing about this calculation is that Yang didn't really need to know much about the nebula," Bellan says. "Just knowing the diameter of the strands and the periodicity of the twist, numbers that can be observed astronomically, Yang was able to predict the angle of twist that yielded an equilibrium structure, and that was consistent with observations of this nebula. One of the most exciting aspects of this research is that magnetohydrodynamics, the theory of magnetized plasmas, turns out to be fantastically scalable. When I first started looking into this, I thought the phenomena of magnetic structures at different scales were qualitatively similar, but because their sizes are so different, they couldn't be described by the same equations. It turns out that this is not so. What we see in lab experiments and in solar and astrophysical observations are governed by the same equations."

The paper, titled "Magnetic Double Helix," was published in Physical Review Letters. The work was funded by the National Science Foundation.

Source: Caltech/News

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Contact:

Caltech Media Relations
mr@caltech.edu

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Following Photons Through Curved Spacetimes

Today’s featured image is a beautiful representation of how simulated images of active black holes are made. In a recent research article, a team led by Aniket Sharma (Indian Institute of Science Education and Research Mohali) introduced Mahakala, a new ray-tracing algorithm that expertly tracks photons as they navigate the warped spacetimes surrounding black holes. Mahakala is named for the Egyptian deity who, as Sharma and collaborators describe, is “believed to be the depiction of absolute black, and the one who has the power to dissolve time and space into himself.” The image above shows a simulated accreting black hole at a wavelength of 1.3 millimeters, which is the same wavelength used by the Event Horizon Telescope to view the supermassive black holes at the center of the Milky Way and the galaxy Messier 87. The dotted lines streaming off to the right represent the paths that photons took on their way to the viewer as they curved around the black hole, which is visible among the forest of lines. In this representation, the color of each dot shows the synchrotron emission generated at that point in three-dimensional space. The team hopes that Mahakala, which can be run quickly and easily from a Python Jupyter notebook, helps make the complex world of general relativistic magnetohydrodynamics simulations more accessible. You can try it for yourself or learn more from the article linked below.

By Kerry Hensley

Citation

“Mahakala: A Python-Based Modular Ray-Tracing and Radiative Transfer Algorithm for Curved Spacetimes,” Aniket Sharma et al 2025 ApJ 985 40. doi:10.3847/1538-4357/adc104

Source: American Astronomical SocietyAAS-Nova

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A New Way to Measure Black Hole Spin

A Hubble Space Telescope image of the relativistic jet emerging from the active supermassive black hole at the heart of the massive elliptical galaxy Messier 87. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA); Acknowledgment: P. Cote (Herzberg Institute of Astrophysics) and E. Baltz (Stanford University)

Closeup of Messier 87’s relativistic jet.
Credit: NASA and the Hubble Heritage Team (STScI/AURA)

Upgraded interferometers will give researchers a never-before-seen view of the jets of active supermassive black holes. By modeling what might be seen when these instruments come online, researchers have discovered a new way to measure black hole spin.

Black Holes and Relativistic Jets

Galaxies across the universe harbor supermassive black holes. Determining the properties of these black holes — their masses and spins — is key to understanding the formation and evolution of supermassive black holes and how they shape the evolution of their host galaxies.

Some supermassive black holes produce relativistic particle jets that are thought to be powered by the black hole’s spin. This means that precise observations of black hole jets could provide a potential way to measure the spin of a black hole.

Planned and proposed interferometers will stretch observing baselines to great distances — even into space — to attain the high resolution necessary for this sensitive measurement. Building on the successes of the Event Horizon Telescope, a planet-spanning interferometer that has revealed images of the supermassive black holes at the center of the giant elliptical galaxy Messier 87 and the Milky Way, observatories like the Next-Generation Event Horizon Telescope and the Black Hole Explorer will advance our understanding of supermassive black holes and relativistic jets.

Ray-traced polarized image of a collimated black hole jet. The white bars show the direction of polarization, while the color scale shows the normalized intensity. Several abrupt changes in the polarization direction as a function of radius are visible. Credit: Adapted from Gelles et al. 2025

Tracing Rays from Modeled Jets

To learn what might be gleaned from future images of black holes and black hole jets, Zachary Gelles (Princeton University) and collaborators developed a model of a nearly face-on relativistic black hole jet, much like the jet from Messier 87’s black hole. The team’s model incorporates both general relativistic magnetohydrodynamics, which describes a magnetized fluid subjected to the rules of Einstein’s General Theory of Relativity, and force-free electrodynamics, which focuses on the dynamics of the system’s electromagnetic fields.

With this model in hand, the team used ray tracing — following the paths that photons would take through the modeled jet — to predict how the jet would appear in polarized light. Examining the results for jets with varying degrees of narrowness, or collimation, the team noted that the polarization of the most collimated jet behaved strangely, with the polarization angle changing dramatically with position.

Gelles and coauthors demonstrated that one of these sudden polarization changes happens at the black hole’s light cylinder, or the radius at which the jet becomes relativistic and the magnetic field switches from being mostly poloidal to mostly azimuthal. Because the position of the light cylinder is dependent upon the spin of the black hole, measuring the location of this polarization swing allows for a measurement of the black hole’s spin.

Polarization direction as a function of impact parameter, showing the locations and causes of the abrupt changes in polarization angle.  Credit: Gelles et al. 2025

The Promise of Polarization

This method has several potential advantages over other methods. Unlike the current leading method for measuring black hole spin, X-ray spectroscopy, this method applies to low-luminosity active black holes, which are thought to be common throughout the universe. And while the model includes a number of simplifications, the team asserts that incorporating features of more realistic jets, such as asymmetry, is unlikely to change the outcome.

Gelles’s team also showed that the location of the polarization flip for slowly spinning black holes is 10 times farther out than it is for rapidly spinning black holes. What this means in practice is that determining whether a black hole is slowly or rapidly spinning doesn’t require extraordinarily high resolution, just a general sense of where the flip happens.

Looking forward, Gelles’s team plans to continue their simulations, shoring up their predictions until they can be tested when future interferometers come online.

By Kerry Hensley

Source: American Astronomical Society/AAS-Nova

Citation

“Signatures of Black Hole Spin and Plasma Acceleration in Jet Polarimetry,” Z. Gelles et al 2025 ApJ 981 204. doi:10.3847/1538-4357/adb1aa

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M87's Powerful Jet Unleashes Rare Gamma-ray Outburst

Fig. 1: Light curve of the gamma-ray flare (bottom) and collection of quasi-simultaneously observed images of the M87 jet (top) at various scales obtained in radio and X-ray during the 2018 campaign. The telescopes, the wavelength observation range and scale are shown at the top right of each image. © EHT Collaboration, Fermi-LAT Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, EAVN Collaboratio

Multi-wavelength Campaign with Effelsberg and mm-VLBI Arrays Reveals a High-energy Gamma-ray Flare

The shadow of the black hole in Messier 87 has been imaged by with global radio array telescopes over the last years. Joint campaigns have been coordinated annually ever since. An international team of researchers has just released the results of a large campaign on M87 of Event Horizon Telescope and Global mm-VLBI Array observations in 2018, involving over twenty-five ground-based and space-based telescopes. The team, including a number of researchers from the Max Planck Institute for Radio Astronomy in Bonn, Germany, report a spectacular flare at multiple wavelengths from the powerful relativistic jet emanating from the very centre of the same galaxy. This study reveals the first observation in over a decade of a high-energy gamma-ray flare. Photons up to thousands of billions of times the energy of visible light from the supermassive black hole M87* were detected after obtaining nearly simultaneous spectra of that galaxy with the broadest wavelength coverage ever collected.

Millimetre VLBI facilities, represented by two arrays, the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA), the latter coordinated by the Max Planck Institute for Radio Astronomy (MPIfR), are global networks of radio telescopes regularly interconnected to observe the innermost structures of galactic nuclei and to image the shadows of supermassive black holes.

“We were fortunate to detect a gamma-ray flare from M87 during the EHT's multi-wavelength campaign—the first such event in over a decade,” says Giacomo Principe, publication coordinator and researcher at the University of Trieste. “This rare event allowed us to pinpoint the region producing the gamma-ray emission. Recent and upcoming observations with a more sensitive EHT array will provide critical insights into the physics around M87’s supermassive black hole, exploring the disk-jet connection and the origins of gamma-ray photons.”

Messier 87, also known as Virgo A or NGC 4486, is the brightest object in the Virgo cluster of galaxies, the largest gravitationally bound type of structure in the universe. The relativistic jet examined by the researchers is surprising in its extent, reaching sizes that exceed the black hole’s event horizon by tens of millions of times (7 orders of magnitude) - akin to the difference between the size of a bacterium and the largest known blue whale.

The energetic flare, which lasted approximately three days and suggests an emission region of less than three light-days in size (~170 AU, where 1 Astronomical Unit is the distance from the Sun to Earth), revealed a bright burst of high-energy emission—well above the energies typically detected by radio telescopes from the black hole region.

“High-cadence very-high-energy gamma-ray observations during both a steady state and a rare short-term flare—the first in over a decade—were achieved through the collaboration of three imaging high-energy telescope arrays”, explains Alexander Hahn from the Max Planck Institute for Physics, a co-author of the study. “Combined with simultaneous multi-wavelength data at lower energies, these observations offer crucial insights into the extreme processes powering these cosmic events.”

During the campaign, the LAT instrument aboard the Fermi space observatory detected an increase in high-energy gamma-ray flux with energies up to billions of times greater than visible light. The satellites Chandra and NuSTAR then collected high-quality data in the X-ray band. Radio observations with VLBI arrays such as the GMVA, the Very Long Baseline Array (VLBA) and the East Asian VLBI Network (EAVN) show a relativistic jet and an apparent annual change in the jet's position angle within a few milliarcseconds of arc from the galaxy's core.

“The radio imaging provides a unique perspective, allowing astronomers to track the structural and temporal evolution of the jet at unprecedented angular resolutions”, says Thomas Krichbaum of the MPIfR. “In this campaign, radio data not only constrained the jet geometry but also served as a vital reference for correlating the gamma-ray emission with the relativistic jet dynamics.”

Observations show changes in the position of the ring's asymmetry (the black hole's event horizon) and the jet's position. This suggests a physical link between these structures on very different scales. “The first image from the 2017 observational campaign showed that the ring’s emission was uneven, with brighter areas indicating asymmetries. Subsequent 2018 observations confirmed these findings, showing that the position angle of the asymmetry had shifted”, says Daryl Haggard, professor at McGill University and co-coordinator of the EHT multi-wavelength working group.

This is a prime example of how radio observations of the most violent objects in the Universe are complemented by high-energy telescopes like those used in this major campaign. The MPIfR participates in this effort with observations performed with the GMVA and the EHT. These radio data were, among other, postprocessed at the MPIfR correlator facility in Bonn. MPIfR radio telescopes participating in these arrays are the 100-m telescope in Effelsberg and the 12-m APEX telescope in Chile. The 30-m IRAM telescope in Pico Veleta, Spain, recently complemented by the IRAM/NOEMA telescope array in the French Alps, added substantial sensitivity to these observations.

“This observing campaign produced the first image ever showing both the black hole shadow and the jet in M87, presented in April 2023, and now we see that new, exciting results are coming from the coordinated observations carried out around the second global EHT campaign”, recalls Eduardo Ros, astronomer at the MPIfR and European scheduler of the GMVA.

J. Anton Zensus, director at the MPIfR and founding chair of the EHT collaboration, concludes: "The contribution of cutting-edge technology in radio astronomy, in coordination with different facilities on Earth and beyond, shows here in a special way how multi-band studies of sources such as Messier 87 pave the way for stimulating future research and potential breakthroughs in understanding the Universe"

Fig. 2: The observatories and telescopes that participated in the 2018 multiband campaign to detect the high-energy gamma-ray flare from the M87* black hole. © EHT Collaboration, Fermi-LAT Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, EAVN Collaboration.

Source: Max Planck for Radio Astronomy/News

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Additional Information

The EHT collaboration involves more than 400 researchers from Africa, Asia, Europe, North and South America, with around 270 participating in this paper. The international collaboration aims to capture the most detailed images of black holes using a virtual Earth-sized telescope. Supported by considerable international efforts, the EHT links existing telescopes using novel techniques to create a fundamentally new instrument with the highest angular resolving power that has yet been achieved.

The EHT consortium consists of 13 stakeholder institutes; the Academia Sinica Institute of‬ Astronomy and Astrophysics, the University of Arizona, the Center for Astrophysics | Harvard &‬ Smithsonian, the University of Chicago, the East Asian Observatory, the Goethe University‬ Frankfurt, the Institut de Radioastronomie Millimétrique, 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, and the Radboud University.‬‬

The EHT array operating at 1.3 mm wavelength included 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 (KP), and the Greenland Telescope (GLT). The GMVA, observing at adjacent days at a wavelength of 3.5 mm included the 100-m radio telescope in Effelsberg. GMVA and EHT data were post-processed at the MPIfR correlator facility. The EHT data were also correlated at the MIT/Haystack Observatory in Westford, MA, USA. Further analysis was performed in the framework of the global EHT collaboration.

The second EHT and multi-wavelength campaign in 2018 leveraged more than two dozen high-profile observational facilities, including NASA’s Fermi-LAT, the Hubble Space Telescope, NuSTAR, Chandra, and Swift telescopes, together with the world’s three largest Imaging Atmospheric Cherenkov Telescope arrays (H.E.S.S., MAGIC and VERITAS). These observatories are sensitive to X-ray photons as well as high-energy and very-high-energy gamma-rays, respectively.

Researchers affiliated with the Max Planck Institut für Radioastronomie, listed as co-authors in the published research, are: Jae-Young Kim, Ru-sen Lu, and also Walter Alef, Rebecca Azulay, Uwe Bach, Anne-Kathrin Baczko, Silke Britzen, Gregory Desvignes, Sergio A. Dzib, Ralph Eatough, Christian M. Fromm, Michael Janssen, Joana A. Kramer, Michael Kramer, Thomas P. Krichbaum, Mikhail Lisakov, Jun Liu, Kuo Liu, Andrei P. Lobanov, Nicholas R. MacDonald, Nicola Marchili, Karl M. Menten, Cornelia Müller, Hendrik Müller, Gisela Ortiz-Leon, Georgios Filippos Paraschos, Felix Poetzl, Eduardo Ros, Helge Rottmann, Alan L. Roy, Tuomas Savolainen, Lijing Shao, Pablo Torne, Efthalia Traianou, Jan Wagner, Robert Wharton, Maciek Wielgus, Gunther Witzel, J. Anton Zensus, and Guang-Yao Zhao.

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Contact:

Dr. Thomas Krichbaum
tel:+49 228 525-295
tkrichbaum@mpifr-bonn.mpg.de
Max Planck Institute for Radio Astronomy, Bonn

Prof. Dr. J. Anton Zensus
Director and Head of Research Division Radi Astronomy / VLBI
tel:+49 228 525-298
azensus@mpifr-bonn.mpg.de
Max Planck Institute for Radio Astronomy, Bonn

Prof. Dr. Eduardo Ros
tel:+49 228 525-125
ros@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Dr. Norbert Junkes
Press and Public Outreach
tel:+49 228 525-399
njunkes@mpifr-bonn.mpg.de Max Planck Institute for Radio Astronomy, Bonn

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Original Paper

Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode

The Event Horizon Telescope- Multi-wavelength science working group, The Event Horizon Telescope Collaboration, The Fermi Large Area Telescope Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, and EAVN Collaboration. In: A&A, 692, A140 (2024). DOI: 10.1051/0004-6361/202450497 .

Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode

The Event Horizon Telescope- Multi-wavelength science working group, The Event Horizon Telescope Collaboration, The Fermi Large Area Telescope Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, and EAVN Collaboration (arXiv preprint).

Animation

Gamma-ray Flare
Very high energy gamma-ray flare observed by Cherenkov telescopes (H.E.S.S., MAGIC and VERITAS). Credits: EHT Collaboration, Fermi-LAT Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, EAVN Collaboration).

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Links

Radio Astronomy / VLBI
Research Department at MPIfR

Fundamental Physics in Radio Astronomy
Research Department at MPIfR

Millimeter and Submillimeter Astronomy
Research Department at MPIfR

Radio Telescope Effelsberg
Effelsberg 100-m Radio Telescope

EHT
Event Horizon Telescope (EHT)

GMVA
Global mm-VLBI Array (GMVA)

VLBA
Very Long Baseline Array (VLBA)

EAVN
East-Asian VLBI Network (EAVN)

Fermi LAT
The Fermi Large Area Telescope (LAT)

H.E.S.S.
The H.E.S.S. Collaboration

MAGIC
The MAGIC Telescopes

VERITAS
VERITAS (Very Energetic Radiation Imaging Telescope Array System)

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Parallel Press Releases

CfA Astronomers Help Catch Rare Gamma-Ray Outburst from M87’s Powerful Jet
Harvard/CfA Press Release, December 13, 2024

Event Horizon Telescope: rare gamma-ray burst observed from M87, UniTS also involved
UniTS Press Release, December 13, 2024

The Event Horizon Telescope Collaboration Reports a Spectacular Flare from the Centre of the Messier 87 Galaxy
CITA Press Release, December 13, 2024

M87's powerful jet unleashes rare gamma-ray outburst
Press Release Nagoya City University/Eurekalert, December 13, 2024

Brillamento di luce gamma nel getto di M87
INAF Press Release, December 13, 2024

L’INATTESO BRILLAMENTO NEL GETTO DI M87 OSSERVATO DALLE ONDE RADIO AI RAGGI GAMMA
INFN Press Release, December 13, 2024

【プレスリリース】M87のジェットから強力なガンマ線フレアを検出〜EHTと多波長観測が捉えた巨大ブラックホールの活動期〜
Press Release ICRR/Univ. Tokyo, December 13, 2024

M87 のジェットから強力なガンマ線フレアを検出 〜EHT と多波長観測が捉えた巨大ブラックホールの活動期〜
Kogakuin University Press Release, December 13, 2024

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EHT scientists make highest-resolution observations yet from the surface of Earth

PR Image eso2411a
Illustration of the highest-resolution detections ever made from the surface of Earth

PR Image eso2411b
Location of the observatories used in an EHT pilot experiment

PR Image eso2411c
Computer simulation illustrating how a black hole looks like at different wavelengths

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Videos

PR Video eso2411a
Sharpest ground observations ever | ESO Chasing Starlight


PR Video eso2411b
Animation of the highest-resolution detections ever made from the surface of Earth

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The Event Horizon Telescope (EHT) Collaboration has conducted test observations, using the Atacama Large Millimeter/submillimeter Array (ALMA) and other facilities, that achieved the highest resolution ever obtained from the surface of Earth [1]. They managed this feat by detecting light from distant galaxies at a frequency of around 345 GHz, equivalent to a wavelength of 0.87 mm. The Collaboration estimates that in future they will be able to make black hole images that are 50% more detailed than was possible before, bringing the region immediately outside the boundary of nearby supermassive black holes into sharper focus. They will also be able to image more black holes than they have done so far. The new detections, part of a pilot experiment, were published today in The Astronomical Journal.

The EHT Collaboration released images of M87*, the supermassive black hole at the centre of the M87 galaxy, in 2019, and of Sgr A*, the black hole at the heart of our Milky Way galaxy, in 2022. These images were obtained by linking together multiple radio observatories across the planet, using a technique called very long baseline interferometry (VLBI), to form a single ‘Earth-sized’ virtual telescope.

To get higher-resolution images, astronomers typically rely on bigger telescopes — or a larger separation between observatories working as part of an interferometer. But since the EHT was already the size of Earth, increasing the resolution of their ground-based observations called for a different approach. Another way to increase the resolution of a telescope is to observe light of a shorter wavelength — and that’s what the EHT Collaboration has now done.

“With the EHT, we saw the first images of black holes using the 1.3-mm wavelength observations, but the bright ring we saw, formed by light bending in the black hole’s gravity, still looked blurry because we were at the absolute limits of how sharp we could make the images,” said the study's co-lead Alexander Raymond, previously a postdoctoral scholar at the Center for Astrophysics | Harvard & Smithsonian (CfA), and now at the Jet Propulsion Laboratory, both in the United States. “At 0.87 mm, our images will be sharper and more detailed, which in turn will likely reveal new properties, both those that were previously predicted and maybe some that weren’t.”

To show that they could make detections at 0.87 mm, the Collaboration conducted test observations of distant, bright galaxies at this wavelength [2]. Rather than using the full EHT array, they employed two smaller subarrays, both of which included ALMA and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile. The European Southern Observatory (ESO) is a partner in ALMA and co-hosts and co-operates APEX. Other facilities used include the IRAM 30-meter telescope in Spain and the NOrthern Extended Millimeter Array (NOEMA) in France, as well as the Greenland Telescope and the Submillimeter Array in Hawaiʻi.

In this pilot experiment, the Collaboration achieved observations with detail as fine as 19 microarcseconds, meaning they observed at the highest-ever resolution from the surface of Earth. They have not been able to obtain images yet, though: while they made robust detections of light from several distant galaxies, not enough antennas were used to be able to accurately reconstruct an image from the data.

This technical test has opened up a new window to study black holes. With the full array, the EHT could see details as small as 13 microarcseconds, equivalent to seeing a bottle cap on the Moon from Earth. This means that, at 0.87 mm, they will be able to get images with a resolution about 50% higher than that of previously released M87* and SgrA* [3] 1.3-mm images. In addition, there’s potential to observe more distant, smaller and fainter black holes than the two the Collaboration has imaged thus far.

EHT Founding Director Sheperd “Shep” Doeleman, an astrophysicist at the CfA and study co-lead, says: “Looking at changes in the surrounding gas at different wavelengths will help us solve the mystery of how black holes attract and accrete matter, and how they can launch powerful jets that stream over galactic distances.”

This is the first time that the VLBI technique has been successfully used at the 0.87 mm wavelength. While the ability to observe the night sky at 0.87 mm existed before the new detections, using the VLBI technique at this wavelength has always presented challenges that took time and technological advances to overcome. For example, water vapour in the atmosphere absorbs waves at 0.87 mm much more than it does at 1.3 mm, making it more difficult for radio telescopes to receive signals from black holes at the shorter wavelength. Combined with increasingly pronounced atmospheric turbulence and noise buildup at shorter wavelengths, and an inability to control global weather conditions during atmospherically sensitive observations, progress to shorter wavelengths for VLBI — especially those that cross the barrier into the submillimetre regime — has been slow. But with these new detections, that’s all changed.

"These VLBI signal detections at 0.87 mm are groundbreaking since they open a new observing window for the study of supermassive black holes", states Thomas Krichbaum, a co-author of the study from the Max Planck Institute for Radio Astronomy in Germany, an institution that operates the APEX telescope together with ESO. He adds: "In the future, the combination of the IRAM telescopes in Spain (IRAM-30m) and France (NOEMA) with ALMA and APEX will enable imaging of even smaller and fainter emission than has been possible thus far at two wavelengths, 1.3 mm and 0.87 mm, simultaneously."

Source: ESO/News

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Notes

[1] There have been astronomical observations with higher resolution, but these were obtained by combining signals from telescopes on the ground with a telescope in space: https://www.mpifr-bonn.mpg.de/pressreleases/2022/2. The new observations released today are the highest-resolution ones ever obtained using only ground-based telescopes.

[2] To test their observations, the EHT Collaboration pointed the antennas to very distant ‘active’ galaxies, which are powered by supermassive black holes at their cores and are very bright. These types of sources help to calibrate the observations before pointing the EHT to fainter sources, like nearby black holes.

[3] The GRAVITY instrument on ESO’s Very Large Telescope Interferometer has also obtained extremely detailed observations of Sgr A*, pinpointing the exact location of the black hole and the material orbiting it with an accuracy of a few tenths of microarcseconds.

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More information

This EHT Collaboration research was presented in a paper by A. W. Raymond et al. published today in The Astronomical Journal (doi: 10.3847/1538-3881/ad5bdb).

The EHT Collaboration involves more than 400 researchers from Africa, Asia, Europe, North and South America, with around 270 participating in this paper. The international collaboration aims to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international efforts, the EHT links existing telescopes using novel techniques — creating a fundamentally new instrument with the highest angular resolving power that has yet been achieved.

The EHT consortium consists of 13 stakeholder institutes; the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the Center for Astrophysics | Harvard & Smithsonian, the University of Chicago, the East Asian Observatory, Goethe University Frankfurt, Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, National Astronomical Observatory of Japan, Perimeter Institute for Theoretical Physics, and Radboud University.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

The Atacama Pathfinder EXperiment (APEX) is a 12-metre-diameter telescope, operating at millimetre and submillimetre wavelengths — between infrared light and radio waves. ESO operates APEX at one of the highest observatory sites on Earth, at an elevation of 5100 metres, high on the Chajnantor plateau in Chile’s Atacama region. APEX is a project of the Max Planck Institute for Radio Astronomy (MPIfR), hosted and operated by ESO on behalf of the MPIfR.

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, Czechia, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.

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Links

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Contacts:

Shep Doeleman
Center for Astrophysics | Harvard & Smithsonian
Cambridge, MA, United States
Tel: +1-617-496-7762
Email: sdoeleman@cfa.harvard.edu

Thomas Krichbaum
Max Planck Institute for Radio Astronomy
Bonn, Germany
Tel: +49 228 525 295
Email: tkrichbaum@mpifr-bonn.mpg.de

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: press@eso.org

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Cosmic Simulation Reveals How Black Holes Grow and Evolve

This still from the simulation shows a supermassive black hole, or quasar, surrounded by a swirling disk of material called an accretion disk. Credit: Caltech/Phil Hopkins group

An earlier still from the simulation shows a tangle of merging galaxies.
Credit: Caltech/Phil Hopkins group

Hopkins Group: Simulation Zooms Into Black Hole

The new simulation flies into a tangle of merging galaxies, ultimately zooming into an active supermassive black hole, or quasar, surrounded by a swirling disk of material called an accretion disk. A filamentary stream of gas has been wound up into the disk, funneling gas in at a rate sufficient to fuel the brightest known quasars in the universe. Near the end of the simulation, magnetic fields rip away the angular momentum from the rotating disk, which allows material to spiral in further and further until it reaches the event horizon of the black hole, where it can't escape. During this simulation, which represents one moment in time, the scale zooms in by a factor of a billion. The colors show the density of the gas, with brighter colors representing higher densities. Credit: Caltech/Phil Hopkins group

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A team of astrophysicists led by Caltech has managed for the first time to simulate the journey of primordial gas dating from the early universe to the stage at which it becomes swept up in a disk of material fueling a single supermassive black hole. The new computer simulation upends ideas about such disks that astronomers have held since the 1970s and paves the way for new discoveries about how black holes and galaxies grow and evolve.

"Our new simulation marks the culmination of several years of work from two large collaborations started here at Caltech," says Phil Hopkins, the Ira S. Bowen Professor of Theoretical Astrophysics.

The first collaboration, nicknamed FIRE (Feedback in Realistic Environments), has focused on the larger scales in the universe, studying questions such as how galaxies form and what happens when galaxies collide. The other, dubbed STARFORGE, was designed to examine much smaller scales, including how stars form in individual clouds of gas. "But there was this big gap between the two," Hopkins explains. "Now, for the first time, we have bridged that gap." To do that, the researchers had to build a simulation with a resolution that is more than 1,000 times greater than the previous best in the field.

To the team's surprise, as reported in The Open Journal of Astrophysics, the simulation revealed that magnetic fields play a much larger role than previously believed in forming and shaping the huge disks of material that swirl around and feed the supermassive black holes. "Our theories told us the disks should be flat like crepes," Hopkins says. "But we knew this wasn't right because astronomical observations reveal that the disks are actually fluffy—more like an angel cake. Our simulation helped us understand that magnetic fields are propping up the disk material, making it fluffier."

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Cosmic Simulation Reveals How Black Holes Grow and Evolve

Visualizing the Activity Around Supermassive Black Holes Using "Super Zoom-Ins"

In the new simulation, the researchers performed what they call a "super zoom-in" on a single supermassive black hole, a monstrous object that lies at the heart of many galaxies, including our own Milky Way. These ravenous, mysterious bodies contain anywhere from thousands to billions of times the mass of the Sun, and thus exert a huge effect on anything that comes near.

Astronomers have known for decades that as gas and dust are pulled in by the tremendous gravity of these black holes, they are not immediately sucked in. Instead, the material first forms a rapidly swirling disk called an accretion disk. And as the material is just about to fall in, it radiates a huge amount of energy, shining with a brilliance unmatched by just about anything in the universe. But much is still not known about these active supermassive black holes, called quasars, and how the disks that feed them form and behave.

While disks around supermassive black holes have been imaged previously—the Event Horizon Telescope imaged disks circling black holes at the heart of our own galaxy in 2022 and Messier 87 in 2019—these disks are much closer and more tame than the ones that churn around quasars. To visualize what happens around these more active and distant black holes, astrophysicists turn to supercomputer simulations. They feed information about the physics at work in these galactic settings—everything from the basic equations that govern gravity to how to treat dark matter and stars—into thousands of computing processors that work in parallel. This input includes many algorithms, or series of instructions, for the computers to follow to recreate complicated phenomena. So, for example, the computers know that once gas becomes dense enough, a star forms. But the process is not that straightforward.

"If you just say gravity pulls everything down and then eventually the gas forms a star and stars just build up, you'll get everything wildly wrong," Hopkins explains. After all, stars do many things that affect their surroundings. They shine radiation that can heat up or push surrounding gas. They blow winds like the solar wind created by our own Sun, which can sweep up material. They explode as supernovae, sometimes launching material clear out of galaxies or changing the chemistry of their surroundings. So, the computers must know all the ins and outs of this "stellar feedback" as well, as it regulates how many stars a galaxy can actually form.

Building a Simulation that Spans Multiple Scales

But at these larger scales, the set of physics that are most important to include and what approximations can be made differ from those at smaller scales. For example, on the galactic scale, the complicated details of how atoms and molecules behave are extremely important and must be built into any simulation. However, scientists agree that when simulations focus on the more immediate area around a black hole, molecular chemistry can be mostly ignored because the gas there is too hot for atoms and molecules to exist. Instead, what is exists there is hot ionized plasma.

Creating a simulation that could cover all the relevant scales down to the level of a single accretion disk around a supermassive black hole was a huge computational challenge—one that also required a code that could handle all the physics. "There were some codes that had the physics that you needed to do the small-scale part of the problem and some codes that had the physics that you needed to do the larger, cosmological part of the problem, but nothing that had both," Hopkins says.

The Caltech-led team used a code they call GIZMO for both the large- and small-scale simulation projects. Importantly, they built the FIRE project so that all the physics they added to it could work with the STARFORGE project, and vice versa. "We built it in a very modular way, so that you could flip on and off any of the pieces of physics that you wanted for a given problem, but they were all cross compatible," Hopkins says.

This allowed the scientists in the latest work to simulate a black hole that is about 10 million times the mass of our Sun, beginning in the early universe. The simulation then zooms in on that black hole at a moment when a giant stream of material is torn off a cloud of star-forming gas and begins to swirl around the supermassive black hole. The simulation can continue zooming in, resolving a finer area at each step as it follows the gas on its way toward the hole.

Surprisingly Fluffy, Magnetic Disks

"In our simulation, we see this accretion disk form around the black hole," Hopkins says. "We would have been very excited if we had just seen that accretion disk, but what was very surprising was that the simulated disk doesn't look like what we've thought for decades it should look like." In two seminal papers from the 1970s that described the accretion disks fueling supermassive black holes, scientists assumed that thermal pressure—the change in pressure caused by the changing temperature of the gas in the disks—played the dominant role in preventing such disks from collapsing under the tremendous gravity they experience close to the black hole. They acknowledged that magnetic fields might play a minor role in helping to shore up the disks. In contrast, the new simulation found that the pressure from the magnetic fields of such disks was actually 10,000 times greater than the pressure from the heat of the gas.

"So, the disks are almost completely controlled by the magnetic fields," Hopkins says. "The magnetic fields serve many functions, one of which is to prop up the disks and make the material puffy."

This realization changes a host of predictions scientists can make about such accretion disks, such as their mass, how dense and thick they should be, how fast material should be able to move from them into a black hole, and even their geometry (such as whether the disks can be lopsided).

Looking forward, Hopkins hopes this new ability to bridge the gap in scales for cosmological simulations will open many new avenues of research. For example, what happens in detail when two galaxies merge? What types of stars form in the dense regions of galaxies where conditions are unlike those in our Sun's neighborhood? What might the first generation of stars in the universe have looked like? "There's just so much to do," he says.

The new simulation is detailed in a paper entitled "FORGE'd in FIRE: Resolving the End of Star Formation and Structure of AGN Accretion Disks from Cosmological Initial Conditions," which appears in The Open Journal of Astrophysics. Additional authors on the paper include Michael Grudic (PhD '19) of Carnegie Observatories, Kung-Yi Su (PhD '19) of Harvard University, Sarah Wellons of Wesleyan University, Daniel Angles-Alcazar of the University of Connecticut and the Flatiron Institute, Ulrich Steinwandel of the Flatiron Institute, David Guszeinov (PhD '18) of the University of Texas at Austin, Norman Murray (BS '79) of the University of Toronto, Claude-Andre Faucher-Giguere of Northwestern University, Eliot Quatert of Princeton University, and Dusan Keres of UC San Diego. Hopkins's work was supported by funding from the National Science Foundation and NASA.

Written by Kimm Fesenmaier

Source: Caltech/News

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Contact:

Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu

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