Research Highlights
Here we show recent research results from the Radio Astronomy/Very-Long-Baseline Interferometry department.
Faster Imaging for the Next Generation of Radio Telescopes
3 February 2026
Radio interferometers reconstruct images of the sky from incomplete Fourier measurements, a task traditionally handled by the widely used CLEAN algorithm. In a new study led by MPIfR-affiliated scientist Hendrik Müller and published today in Astronomy & Astrophysics, researchers show how techniques from convex optimization can significantly accelerate this cornerstone method. By interpreting CLEAN as a Newton-type optimization scheme, the team incorporates well-known acceleration strategies such as Nesterov acceleration and conjugate gradient method directly into the algorithm’s major and minor loop framework. The resulting approach remains simple and compatible with existing imaging pipelines, yet converges several times faster and reaches substantially deeper residual levels. The results demonstrate that CLEAN can achieve order-of-magnitude improvements in convergence speed and dynamic range, an important step toward efficient data processing for future high-data-rate radio interferometers. The method provides a practical pathway to faster and more powerful imaging while retaining the robustness that has made CLEAN the standard in radio astronomy. More information, in the original paper here.
The Most Extreme AGN: Outbursts, Changing Looks, and Binary Black Holes
30 January 2026
How extreme can variability in active galactic nuclei (AGN) become — and what does it reveal about the physics of supermassive black holes? A new review led by MPIfR astronomer S. Komossa in Advances in Space Research (see here) explores the most dramatic cases of AGN variability, including giant outbursts, deep fading states, exceptional spectral changes, semi-periodic signals, and the fascinating class of changing-look (CL) AGN. Drawing on long-term, densely sampled light curves and follow-up spectroscopy, the study proposes a refined classification scheme for CL phenomena, distinguishing between slow and fast transitions, repeating events, and “frozen-look” AGN that show no emission-line response. The remarkable diversity in optical and X-ray behavior points to distinct intrinsic mechanisms within the accretion disk and broad-line region. The paper also addresses how to distinguish true changing-look AGN from look-alike events such as tidal disruption events or supernovae, and presents the latest multiwavelength results on the binary supermassive black hole candidate OJ 287 from the MOMO project. New constraints, including a comparatively low primary black hole mass of about 10⁸ solar masses, challenge existing binary models and imply that OJ 287 is no longer a near-future target for pulsar timing arrays.
Magnetic Fields at the Edge of M 87*
16 January 2026
How are magnetic fields structured near a supermassive black hole — and how do they shape what the Event Horizon Telescope (EHT) sees? In a new study led by Saurabh, PhD candidate at the Max Planck Institute for Radio Astronomy, semi-analytic models are used to investigate the accretion flow around M 87*, combining Kerr spacetime calculations with fully polarized general relativistic ray-tracing to produce synthetic EHT images. By varying magnetic field geometry, plasma dynamics, disk thickness, and black hole spin, the study shows that magnetic configuration and radial inflow strongly affect observable properties, while disk thickness plays only a minor role. The results favor a scenario in which poloidal magnetic fields with partially radial inflow dominate the flow near the event horizon, with moderate to high prograde spin preferred. The work strengthens the theoretical link between polarized EHT observations and the physical conditions powering relativistic jets. For more information, see the original publication here.
Cosmic Dance of Light and Magnetism Around a Black Hole Jet
08 January 2026
New Event Horizon Telescope images reveal how shock waves and magnetic turbulence interact in the jet of a supermassive black hole, offering an unprecedented look at how these cosmic “engines” are powered.
An international team has used the Event Horizon Telescope (EHT) to obtain the first direct, spatially resolved view of shock waves interacting with magnetic turbulence inside the jet of a supermassive black hole. The findings, published today in Astronomy & Astrophysics (see link here), capture rapid changes occurring extremely close to the black hole, in the region where jets are shaped and energized.
A close-up view of OJ 287
The target of the observations is OJ 287, a well-known active galaxy about 1.6 billion light-years away in the constellation Cancer. OJ 287 has shown dramatic activity for more than a century and is often discussed as a possible binary supermassive black hole system. Its long-term variability makes it an important natural laboratory for studying how black holes feed and how jets respond.
With the EHT’s extraordinary resolving power—comparable to spotting a tennis ball on the Moon—the team imaged the innermost region of the jet and identified two compact bright features moving outward at different speeds. These features behave like propagating shocks, compressing and heating the plasma as they travel.
Polarized light reveals a twisted magnetic field
The key breakthrough comes from polarization, which encodes information about magnetic fields. As the two shock features move through the inner jet, the polarization direction of their emitted light rotates. Remarkably, the two features rotate in opposite directions. This pattern provides strong evidence that the jet is threaded by a helical (corkscrew-like) magnetic field and that the moving shocks illuminate different parts (phases) of that magnetic structure.
The images also show that the jet is not simply straight and smooth. Instead, it displays a twisted, wave-like shape consistent with Kelvin–Helmholtz instabilities—a common physical effect that occurs when adjacent layers of a flow move at different speeds, generating waves and vortices. In the case of OJ 287, such instabilities can create a spiral pattern in the jet plasma, shaping where shocks brighten and how polarization evolves.
Changes seen over just five days
The analysis is based on EHT observations taken over five days in April 2017. Over this short interval, the jet’s structure and its polarization changed substantially, demonstrating that the inner jet is a highly dynamic environment. Denser time coverage in future observing campaigns would make it possible to follow these interactions more continuously and reconstruct the jet’s evolving magnetic geometry more completely.
Event Horizon Telescope observations of OJ 287 on April 5 and 10, 2017, revealing the jet structure at unprecedented resolution just 0.75 light-years from the supermassive black hole. The polarization images (left panels) show three bright components that visibly evolve over the five-day interval, the shortest timescale on which such changes have been directly imaged in this source. The two innermost components exhibit opposite-direction polarization rotations: the faster-moving component C1/P1 (blue-cyan arrows) rotates counterclockwise by +18° while the slower component C2/P2 (pink-magenta arrows) rotates clockwise by -12°. Component C3*/P3* further downstream displays radial polarization characteristic of a recollimation shock. The schematic (right) illustrates how shock components (green arrows) propagating at different speeds through the jet interact with a helical Kelvin-Helmholtz wave pattern (orange lines), sampling different phases of the helical magnetic field (blue lines) and producing the observed opposite rotations. (Gómez, J. L., Cho, I., Traianou, E., et al., A&A 2026, DOI: 10.1051/0004-6361/202555831)
Turning global telescope data into polarization images
Producing reliable polarization maps at EHT resolution is technically demanding. Polarization signals are comparatively faint and can be strongly affected by small instrumental imperfections at each telescope. The analysis therefore requires careful calibration, extensive validation, and cross-checks using multiple independent imaging approaches to ensure that the detected polarization patterns reflect the source itself.
Relativistic jets are among the most powerful phenomena in the Universe, capable of transporting energy across thousands of light-years. Yet key questions remain: how jets are launched, how they remain collimated, where shocks form, and how particles are accelerated to extreme energies. By directly resolving shock features and connecting their polarization behavior to instabilities and magnetic field structure, these EHT observations provide new, stringent tests for theoretical models and for numerical simulations of jet dynamics.
This result opens a new observational window into jet physics close to the black hole, where magnetic fields, turbulence, and shocks interact on the smallest accessible scales.
Our Team
The study is led by a group of radio astronomers including the following MPIfR affiliates: Efthalia Traianou, Thomas P. Krichbaum, Guang-Yao Zhao, Yuri Y. Kovalev, and Stefanie Komossa. Additionally, these other colleagues participating in the publication are also affiliated to the MPIfR: Walter Alef, Rebecca Azulay, Uwe Bach, Anne-Kathrin Baczko, Silke Britzen, Gregory Desvignes, Sergio A. Dzib, Ralph P. Eatough, Christian M. Fromm, Michael Janßen, Ramesh Karuppusamy, Jae-Young Kim, Joana A. Kramer, Michael Kramer, Jun Liu, Andrei P. Lobanov, Rusen Lu, Nicholas R. MacDonald, Nicola Marchili, Karl M. Menten, Cornelia Müller, Dhanya G. Nair, Georgios Filippos Paraschos, Eduardo Ros, Helge Rottmann, Alan L. Roy, Saurabh, Tuomas Savolainen, Lijing Shao, Pablo Torne, Jan Wagner, Robert Wharton, Gunther Witzel, and J. Anton Zensus.
Event Horizon Telescope maps twisting magnetic fields near the supermassive binary black hole candidate OJ287
Jets, Disks, and the Baldwin Effect: A New Look at Mg II in Blazars
9 January 2026
In a new study published in Astronomy & Astrophysics (see here) led by Víctor M. Patiño Álvarez, head of the MPIfR partner group at INAOE (Puebla, Mexico), the relationship between the Mg II λ2798 Å emission line and the 3000 Å continuum luminosity is revisited for an unprecedented sample of 40,685 radio-quiet quasars and 441 flat-spectrum radio quasars (FSRQs).
By carefully accounting for variability and excluding more than 3,000 radio-loud sources, the team refines the empirical Mg II–continuum relation and examines the origin of the Baldwin effect. They find statistically significant differences between radio-quiet quasars and blazars: the slope of the line–continuum relation — and thus the Baldwin effect — differs systematically between the two populations. This suggests either intrinsic differences in their accretion disk spectra or an additional contribution from jet-driven continuum emission affecting the ionization of the broad line region.
The study also shows that the Baldwin effect arises naturally from the underlying line–continuum relation itself, without requiring an additional physical mechanism. The results provide new insight into how jets and accretion disks jointly shape the emission-line properties of active galaxies.