Do large galactic structures like bipolar jets emitted from active galactic nuclei disprove the YEC biblical chronology? The Anisotropic Synchrony Convention (ASC) model, as a framework for reconciling biblical timelines with observed cosmic features, asserts that these structures can exist within a creation time frame of under 10,000 years.

Alors que l'été va bientôt commencer sur le calendrier, le fléau des coups de soleil, indissociable des fortes chaleurs, est lui aussi de retour. Cependant, cette année, une innovation pourrait bien changer la donne.

Many galaxies, including our own, have a central supermassive black hole. In certain galaxies, gas becomes ensnared in the black hole’s gravitational pull and collects in a disk that feeds the black hole, forming an active galactic nucleus (AGN). An AGN can feast on this disk of gas and dust for millions to billions of years — glowing across the electromagnetic spectrum, brandishing relativistic jets, and creating a brilliant, variable light show visible from billions of light-years away.

Today’s Monthly Roundup investigates the connection between AGNs and neutrinos, considers the question of AGN variability, and explores modeling techniques for relativistic environments.

A Search for Neutrinos from X-Ray-Bright AGNs

Where do neutrinos — neutral, nearly massless elementary particles — come from? AGNs have emerged as one likely source; in 2022, the IceCube collaboration reported evidence for neutrinos from the nearby galaxy Messier 77, which hosts an X-ray-bright AGN, and earlier observations potentially linked a neutrino to the blazar TXS 0506+056.

To investigate the possible connection between neutrinos and X-ray-bright AGNs, the IceCube collaboration performed a dedicated search for neutrinos toward a collection of X-ray-bright AGNs in the northern sky. The team’s initial analysis confirmed that Messier 77 is the strongest source of neutrinos in that area. Focusing specifically on X-ray-bright AGNs with hard X-ray fluxes at least 20% of Messier 77’s flux — 47 AGNs in total — the team found evidence for a possible neutrino excess toward 11 of the galaxies, with NGC 7469 being the strongest candidate.

This result suggests that X-ray-bright AGNs are indeed a plausible source of neutrinos. As for the specific physical origin of these AGN-generated neutrinos, the data provide a few clues. The X-ray emission of an AGN is thought to arise from a billion-degree cloud of plasma called the corona. The interaction of coronal X-rays with high-energy protons is thought to produce neutrinos in the energy range of 1–10 teraelectronvolts — roughly the energies of the neutrinos associated with Messier 77 in this study. However, NGC 7469 was associated with neutrinos more energetic than this range, suggesting that not all AGN-produced neutrinos have a coronal origin. Thus, though the body of evidence suggesting that X-ray-bright AGN are a source of neutrinos, the precise mechanism through which these neutrinos are produced remains unknown.

Disk or Jet: Which Varies More?

If there’s one constant when it comes to AGNs, it’s change; observations show that the emission from active galaxies varies on timescales from minutes to decades. Though both the accretion disk and the jet contribute to the overall multiwavelength behavior of an AGN, it’s not yet clear which of these structures is a greater contributor to an AGN’s variability.

Vineet Ojha (Peking University) and coauthors considered AGN variability at optical and mid-infrared wavelengths. Ojha’s team collected a sample of AGN that lie at similar redshifts and fall into one of three categories: narrow-line Seyfert 1 galaxies detected in gamma rays, narrow-line Seyfert 1 galaxies not detected in gamma rays, and broad-line Seyfert 1 galaxies detected in gamma rays. These three classes are distinguished by the presence or absence of relativistic jets as well as their accretion rate; gamma-ray-detected Seyfert 1s likely host jets, and narrow-line Seyfert 1s likely have higher accretion rates than broad-line Seyfert 1s.

Using optical data from the Zwicky Transient Facility and mid-infrared data from the Wide-field Infrared Survey Explorer, the team separated statistical wiggles from true variability and determined which sample of AGNs was most variable. They found that broad-line AGNs detected in gamma rays are the most variable, suggesting that jets are major contributors to AGN variability. Narrow-line AGNs detected in gamma rays are next in line, likely because these AGNs have jets but also have a strong thermal emission component from their accretion disks due to their high rate of accretion. Narrow-line AGNs not detected in gamma rays are the least variable, lacking a jet and dominated by thermal emission. Taken together, these results suggest that AGN variability is mostly jet driven, with some contribution from accretion disk instabilities.

More on AGN Jets: The Slow-Light Effect

The galaxy Messier 87 (M87) hosts one of the most studied AGN jets. M87’s jet is visibly structured, and it exhibits superluminal motion, in which the relativistic plasma appears to move faster than the speed of light. Because the plasma accelerated by an AGN moves so quickly, researchers attempting to model this plasma may opt to use the slow-light approach, in which the evolution of the ambient plasma is modeled simultaneously with the propagation of light through the medium. Though more computationally intensive than the fast-light approach, in which photons zip through a static medium, slow-light techniques are needed in regions of relativistic flows or strong acceleration.

Yuh Tsunetoe (Chinese Academy of Sciences; University of Tsukuba) and collaborators demonstrated their use of the slow-light approach in models of M87’s jet-launching region, where plasma is accelerated to relativistic velocities. The team performed general relativistic magnetohydrodynamics simulations of the accretion disk and jet from M87’s supermassive black hole and compared the results from slow-light and fast-light methods.

The team found that slow-light images tended to be smoother, lacking the looping, helical structures within the jet seen in fast-light images. Slow-light images show more evidence for the superluminal motion that is observed in relativistic jets like M87’s, as well as greater limb brightening and less wobbling motion. The team also investigated the effects of changing the black hole spin, finding greater wobbling in the jet for slow black hole spins and a straighter, wider jet for rapid black hole spins. Overall, Tsunetoe and coauthors found that the slow-light approach generated images that are more consistent with the properties of M87’s jet, demonstrating that the slow-light approach is necessary to capture the behavior of relativistic jets.

Citation

“Evidence for Neutrino Emission from X-Ray-Bright Active Galactic Nuclei with IceCube,” R. Abbasi et al 2026 ApJL 1000 L26. doi:10.3847/2041-8213/ae4aad

“The Relative Contributions of Accretion Disk Versus Jet to the Optical and Mid-Infrared Variability of Seyfert Galaxies,” Vineet Ojha et al 2025 ApJ 994 84. doi:10.3847/1538-4357/ae0a38

“Slow-Light Effect in the Jet-Launching Region of M87,” Yuh Tsunetoe et al 2026 ApJ 1000 29. doi:10.3847/1538-4357/ae43e7

The post Monthly Roundup: Investigating Active Galactic Nuclei appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Jet-Mode Feedback in NGC 5972: Insights from Resolved MUSE, GMRT, and VLA Observations
Authors: Arshi Ali et al.
First Author’s Institution: Savitribai Phule Pune University
Status: Published in ApJ

Voorwerp Galaxies as Laboratories for Active Galactic Nuclei

Supermassive black holes are believed to reside at the centers of nearly all massive galaxies. As supermassive black holes accrete matter, they can release enormous amounts of energy in the form of radiation, winds, and relativistic jets — powering active galactic nuclei and influencing their host galaxies. This process, known as active galactic nucleus feedback, can regulate star formation and the properties of the gas in the interstellar medium, making it a key mechanism for shaping how galaxies form and evolve over cosmic time.

Of the many diverse manifestations of active galactic nuclei, radio “loud” galaxies stand out as powerful laboratories for studying feedback in action. Not only do these galaxies have characteristic [O III] emission lines, but they also host intense radio-emitting lobes of gas that extend well beyond the structure of the galaxy, indicative of jets. (Today’s article refers to these lobes as the extended emission-line region or EELR.)

Originally discovered by a schoolteacher, Voorwerp galaxies are a special category of radio galaxies that are candidate sites of active galactic nucleus activity in terms of their emission-line signatures. Moreover, they exhibit intriguing clouds of ionized gas that may have originated from jets. Figure 1 shows some examples of Voorwerp galaxies. Exploring these galaxies can shed light on how jets interact with the interstellar medium, a major player in active galactic nucleus feedback.

Today’s article focuses on the physical and kinematic properties of one particular Voorwerp galaxy, NGC 5972. This galaxy is interesting for its bizarre, helical structure of ionized gas, as well as hints of a rich history of active galactic nucleus activity. Could jet feedback have played a significant role in the evolution of this galaxy?

Evidence for Relativistic Jets in NGC 5972

To study the interstellar medium of the Voorwerp galaxy, the authors combined observations from multiple instruments that probe different phases of the galaxy’s gas. Specifically, they used data from the Very Large Telescope (VLT), the Giant Metrewave Radio Telescope (GMRT), and the Very Large Array (VLA) to create maps of the ionized gas emission, allowing them to trace the structures and movement of the gas and jet material. Together, these datasets offer a comprehensive, multi-wavelength view of how the radio jet shaped the surrounding interstellar medium. The maps of NGC 5972, shown in Figure 2, display an impressive spiraling structure that could be the result of prolonged active galactic nucleus activity.

When the authors examined the extended emission-line region, they found that the velocity profiles (shown in Figure 3) are closely aligned with the direction of where we would expect to find a radio jet. The enhanced velocities around the jet region likely represent gas that is outflowing due to feedback. The expected amount of energy from a radio jet would have been capable of driving outflows at these velocities. While the structure and movement of the ionized gas give promising hints of jet feedback, astronomers use a tool called Baldwin–Phillips–Terlevich (BPT) analysis to figure out what exactly is ionizing the gas. By comparing the ratio of different emission lines, we can categorize whether the galaxy’s gas was primarily ionized by radiation from an active galactic nucleus, stars, or other processes. The results of the BPT analysis are shown in the left panel of Figure 4. In the case of NGC 5972, the radio jet is mostly ionized by radiation from the active galactic nucleus! However, the gas perpendicular to the jet shows a different signature — one that matches shock waves rather than strong radiation. In addition, the gas in the shock region is more turbulent (right panel of Figure 4). This suggests that the radio jet is not just a byproduct of the active galactic nucleus — it actively disturbs and heats the surrounding gas by way of shocks. This dual process of jet-induced shocks creates a richer picture of how supermassive black holes interact with the interstellar medium.

Putting the Story of NGC 5972 Together

These findings suggest that jet-driven feedback plays a crucial role in shaping the extended emission-line region of NGC 5972 (see Figure 5 for a summary). The interaction between the radio jet and the surrounding gas not only sustains ionization but also influences the gas structure. To further unravel the jet’s impact, future high-resolution radio observations will be essential, providing deeper insights into how active galactic nucleus–driven jets function.

NGC 5972 is more than just a bizarre-looking galaxy — it’s a time capsule, preserving the memory of a powerful supermassive black hole and revealing how its energy continues to shape the galaxy.

Original astrobite edited by Alexandra Masegian.

About the author, Shalini Kurinchi-Vendhan:

After studying astrophysics and literature at Caltech, I moved onto a Fulbright Fellowship in Heidelberg, Germany. I’m passionate about using computer simulations to explore supermassive black holes and galaxy evolution—but I also love poetry and traveling.

The post Written in the Gas: Jet Feedback in a Voorwerp Galaxy appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: You Shall Not Pass! The Propagation of Low-/Moderate-Powered Jets Through a Turbulent Interstellar Medium
Authors: Olga Borodina et al.
First Author’s Institution: Center for Astrophysics | Harvard & Smithsonian
Status: Published in ApJ

The central black holes of some galaxies are surrounded by accretion disks of hot infalling gas. In cases when the accretion disk is massive and highly energetic, this central system forms an active galactic nucleus that outshines the rest of the galaxy. Active galactic nucleus feedback is the process of energetic interactions between the central supermassive black hole and its surroundings. Active galactic nuclei are essential for galaxy quenching, and correctly modeling their contribution is important for accurate cosmological simulations.

Active galactic nuclei release the energy from their accretion via winds, which are widespread outflows, and jets. Jets are collimated, fast outflows of baryonic matter that can spread out from hundreds to tens of thousands of parsecs from their origin. There’s a big range in power for jets, ranging from a low end of around 10³⁸ erg/s to a high end of 10⁴⁶ erg/s. For context, our Sun emits at about 10³³ erg/s.

This study found three different outcomes for the three jet powers (see Figure 1), and these general conclusions held up even when the authors changed the initial randomized structure of the interstellar medium.

The highest-power jets, 10⁴³ erg/s, were easily able to pass through the turbulent environment and reach the outer boundary of the simulation. They mostly traveled along the axis that the jet was launched along, with some lateral expansion.

The intermediate-power jets, 10⁴⁰ erg/s, were highly disrupted and redirected from the axis they were launched along. The jets bent, filled the low-density cavities between the filaments, and produced bubble-like shapes. These jets did make it all the way to the simulation boundary, but at later times and not along the axis they were initialized on. These intermediate-power jets don’t have enough ram pressure — the pressure against the gas due to the jet’s motion — to push through the turbulent structure of the interstellar medium, and they have to fill pre-existing cavities rather than plowing their own. The authors developed an analytic model for the minimum energy needed for jets to be able to plow through the interstellar medium, at approximately 10⁴¹ erg/s.

The jets in the lowest-power case, 10³⁸ erg/s, were stalled out by the interstellar medium within the first kiloparsec of travel. They couldn’t penetrate the higher-density regions of the interstellar medium the way the 10⁴⁰ erg/s case could, and they couldn’t make it to lower-density cavities to expand into.

All three of these cases were slower and shorter than the same power of jets run in a non-turbulent simulation, with the most significant disruption in the lowest-powered jets. This work demonstrates that a turbulent interstellar medium–jet interaction can be the sole cause of observed asymmetric and bent active galactic nucleus jets. By improving our understanding of this small-scale interaction, the authors are contributing to making better active galactic nucleus feedback models in cosmological simulations.

Original astrobite edited by Ansh Gupta.

 

About the author, Lindsey Gordon:

Lindsey Gordon is a fourth-year PhD candidate at the University of Minnesota. She works on active galactic nucleus jets, radio relics, magnetohydrodynamics simulations, and how to use AI to study all those things better.

The post You Shall Not Pass! Active Galactic Nucleus Jets Through the Interstellar Medium appeared first on AAS Nova.

Messier 87, or M87, is a massive elliptical galaxy that hosts one of the best-studied supermassive black holes in the universe. The black hole, commonly called M87*, was the subject of the first-ever photograph of a black hole, which was released by the Event Horizon Telescope collaboration in 2019. Two years after that groundbreaking first photograph was revealed to the public, the collaboration released a set of polarized images of the black hole, illuminating the magnetic field conditions close to the black hole and fueling years of research since.

Today’s Monthly Roundup explores three aspects of this supermassive black hole: how fast it spins, the properties of its relativistic jet, and the source of its powerful flares.

Taking M87’s Black Hole for a Spin

Spin is one of the fundamental parameters describing a black hole, along with mass and electric charge, and it’s a challenging quantity to measure. In a recent research article, Michael Drew (University of Central Lancashire) and collaborators used data from the Event Horizon Telescope from 2017 and 2018 to measure the spin of M87*. Their goal was to measure the angular momentum of the innermost region of the disk of material swirling around the black hole. For a 10-billion-year-old black hole like M87’s, the angular momentum of the inner reaches of the accretion disk is fundamentally linked to the spin of the black hole.

The team’s measurement technique hinges on the existence of relativistic Doppler beaming, which affects the apparent brightness of the fast-spinning material in the black hole’s accretion disk; material moving toward us as the disk rotates appears brighter, while material moving away appears fainter. By comparing the brightness of the brightest and faintest parts of the ring, Drew and coauthors estimated the velocity of the inner edge of the accretion disk. Combining this estimate with a measure of the disk’s inner radius from the Event Horizon Telescope yielded a measurement of the disk’s angular momentum and, by extension, the black hole’s spin.

This method returned a spin parameter of 0.8, which is within the broad range of previous estimates for M87*’s spin (0.1–0.98). Given certain assumptions made in this work, the team expects that this spin measurement is a lower limit on the black hole’s spin.

In addition to measuring the spin, the team also found a range of plausible accretion rates, from 4×10^-5 to 4×10^-1 solar mass per year (about 0.04–400 times the mass of Jupiter). These values are far below the theoretical maximum accretion rate for M87*, suggesting that while M87* is far more active than the black hole at the Milky Way’s center, it’s still fairly calm as far as black holes go. Finally, the team estimated the black hole’s accretion energy per unit time to be 6×10³³–6×10³⁷ Joules per second. These estimates largely overlap with existing estimates for the energy of M87*’s relativistic jet, supporting models in which the jet is powered by accretion.

A New Model for Bright-Edged Jets

One of the most dramatic features of Messier 87 is its prominent jet. Researchers have noted that M87*’s jet exhibits limb brightening, meaning that the jet appears brighter along its edges than in its center. This characteristic is present throughout M87*’s jet, from close to the point at which it’s launched to far down its length, and is also seen in other black hole jets.

So far, simulations have succeeded in producing a limb-brightened jet under carefully tailored conditions, but they have not yet managed to produce this feature across a range of scales and black hole spins. A team led by Yuh Tsunetoe (Black Hole Initiative at Harvard University; University of Tsukuba) aimed to change that with their recent modeling study. The key feature of the team’s model is that the electrons that produce the jet’s prominent radio emission have much higher velocities parallel to the magnetic field lines that thread through the jet than perpendicular to the magnetic field (i.e., the electron distribution is anisotropic). Previous simulations using particle-in-cell methods, in which the behavior of individual particles is tracked, show that this anisotropic electron distribution is expected to arise in a relativistic, turbulent, magnetically dominated plasma.

Tsunetoe’s team used both general relativistic magnetohydrodynamics (GRMHD) and general relativistic force-free electrodynamics (GRFFE) in their modeling. These two modeling techniques have different strengths and weaknesses: GRMHD allows time variations to be studied, but is only effective close to the black hole, while GRFFE applies at a large distance from the black hole, but can only give a time-averaged result. By combining these two methods, the authors were able to generate synthetic radio-frequency images of M87*’s jet and compare them to observations.

The resulting images show a clear limb-brightened jet across a wide range of both radio frequencies and spatial scales, as well as a striking resemblance to observations of the jet. In addition to comparing against existing data, Tsunetoe and collaborators produced images that can be compared against images from future facilities, such as the next-generation Event Horizon Telescope or the Black Hole Explorer. While more work remains to be done in the study of M87*’s jet — the team noted that their model doesn’t yet produce a counter-jet component as bright as what’s seen in observations — this work represents a significant advance in our ability to model the jets from supermassive black holes.

Investigating a Potential Source of Flares

Like many accreting supermassive black holes, M87* exhibits flares of high-energy radiation. These flares are highly variable, sometimes lasting only a couple of days, which suggests that they arise very close to the black hole’s event horizon. Precisely how these flares are generated is still unknown, though magnetic reconnection, in which magnetic fields rearrange and release pent-up magnetic energy, is a strong candidate.

Recently, Siddhant Solanki (University of Maryland) and collaborators investigated the source of M87*’s flares by tracing the paths of photons through a general relativistic magnetohydrodynamics simulation of an accreting spinning supermassive black hole. The simulation captured the region close to the black hole where magnetic reconnection is thought to occur, potentially launching electron–positron pairs that kick background photons up to high energies, powering a flare.

By charting the course of individual photons as they depart from the current sheet — the surface that separates magnetic fields of opposite direction — and navigate the magnetized plasma surrounding the black hole, Solanki and coauthors show that much of the flux from the simulated flares arises within just 5 gravitational radii of the black hole. This supports the hypothesis that quickly varying flares are generated near the black hole’s event horizon.

The timescales of the simulated flares were also instructive. While the simulated flares tended to last about 130 days, each flare was composed of multiple smaller subflares, which lasted roughly as long as the rapid, ~2-day flares seen from M87*. If these flares are truly subflares arrayed within a longer-duration flare, Solanki and collaborators noted, they should have different time variability at long and short wavelengths. This suggests a need for long-term, multiwavelength monitoring of M87* to clarify the source of its flares.

Citation

“New Estimates of the Spin and Accretion Rate of the Black Hole M87*,” Michael Drew et al 2025 ApJL 984 L31. doi:10.3847/2041-8213/adc90e

“Limb-Brightened Jet in M87 from Anisotropic Nonthermal Electrons,” Yuh Tsunetoe et al 2025 ApJ 984 35. doi:10.3847/1538-4357/adc37a

“Modeling of Lightcurves from Reconnection-Powered Very High-Energy Flares from M87*,” Siddhant Solanki et al 2025 ApJ 985 147. doi:10.3847/1538-4357/adcba9

The post Monthly Roundup: The Supermassive Black Hole of Messier 87 appeared first on AAS Nova.

New JWST observations provide a detailed look at the jets of four young stars, revealing shocks, mass loss, and wiggly behavior that hints at a hidden binary companion.

From Cloud to Star to Planetary System

The transformation from a turbulent cloud of hydrogen gas to a star circled by planets is complicated. As stars coalesce from their natal clouds, they gather gas from their surroundings and flatten it into a dense, dusty disk. While feeding on the gas from this disk, young stars launch powerful, narrow jets and broad, slower-moving winds. As accretion slows, planets begin to form, getting their start from clumps of dust grains.

In a recent research article, JWST observations give insight into the details of this process, illuminating the winds and jets of the disks surrounding young stars.

JWST’s View

Naman Bajaj (Lunar and Planetary Laboratory, The University of Arizona) and collaborators investigated four protoplanetary disks with JWST’s Near Infrared Spectrograph (NIRSpec). The four disks — Tau 042021, HH 30, FS Tau B, and IRAS 04302 — reside in the Taurus star-forming region, which is 1–2 million years old and roughly 450 light-years away.

Each of these disks displays narrow jets that emerge perpendicularly above and below the disk, nested within broad, cone-shaped winds. The disks were selected for their edge-on appearance, which highlights the jets and winds that emerge from the disk.

Bajaj’s team identified more than 40 emission lines for each disk, allowing them to determine the properties of the jets, such as the density and shock speed. One important aspect that can be gleaned from these observations is an estimate of the mass carried away by the jets. Using three independent methods, the team found that jet mass-loss rates for the four disks was on average a billionth of a solar mass per year.

The Wiggly Jet of Tau 042021

Though appearing to jut straight out from the disk, each of the jets studied showed signs of side-to-side wiggles. Tau 042021’s jets are especially interesting, displaying mirror-symmetric wiggling, in which the redshifted and blueshifted wiggles mirror one another. At present, the only explanation for these synchronized wiggles is a binary companion. By modeling the jet wiggles as emanating from a star in a binary system, the authors concluded that Tau 042021 likely contains a 0.33-solar-mass star and a 0.07-solar-mass star in a 2.5-year orbit with a separation of 1.35 au.

Bajaj and coauthors presented a rich dataset that illuminates the behavior of jets from young stars, and their work isn’t yet done; this is the second research article the team has produced from these data, and more are in the works.

Citation

“Class I/II Jets with JWST: Mass-Loss Rates, Asymmetries, and Binary-Induced Wigglings,” Naman S. Bajaj et al 2025 AJ 169 296. doi:10.3847/1538-3881/adc73c

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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.

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.

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.

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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