M2FINDERS - Highlights

An international team of scientists led by Dr. LU Rusen from the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences and affiliated to the MPI für Radioastronomie has used new millimeter-wavelength observations to produce an image that shows, for the first time, both the ring-like accretion structure around a black hole, where matter falls into the black hole, and the black hole's associated powerful relativistic jet. The source of the images was the central black hole of the prominent radio galaxy Messier 87.

An international team of scientists studying the supermassive black hole at the heart of the M87 galaxy have revealed the origins of the monster’s powerful jet and imaged the jet and its source together for the first time. What’s more, the observations have revealed that the black hole’s ring is much larger than scientists previously believed. The observations were published on April 26, 2023 in Nature.

ERC Advanced Grants: 209 top researchers awarded over €500m - Positive trend for female grantees continues

An international team of scientists led by Dr. LU Rusen from the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences and affiliated to the MPI für Radioastronomie (leader of a Partner Group) has used new millimeter-wavelength observations to produce an image that shows, for the first time, both the ring-like accretion structure around a black hole, where matter falls into the black hole, and the black hole's associated powerful relativistic jet. The source of the images was the central black hole of the prominent radio galaxy Messier 87.

The study was published in Nature on April 26.

Super-massive black holes are found at the centers of many galaxies. But all efforts to detect them directly suffer from the fact that no information from their interior can reach us directly. Now, Professor Anton Zensus, director at the Max Planck Institute for Radio Astronomy in Bonn and founding chairman of the Event Horizon Telescope collaboration (EHT), has proposed an independent method to filter out those explanations from the existing ones that are viable. At the same time, this method may succeed in explaining the high-energy plasma outflows ejected by many black holes. The project is funded with an ERC Advanced Grant worth 2.5 million euros.

Magnetic fields in the centres of active galaxies. Left: polarized radiation from the black hole in M87. Center: simulations of the photosphere around the central black hole and the jet in M87. Right: artist's view of the central engine ("jet engine").

Der Europäische Forschungsrat ERC fördert die Professoren Ulf-G. Meißner und Anton Zensus mit zwei seiner begehrten „Advanced Grants“ für Grundlagenforschung.

09 August 2023

F. Eppel, M. Kadler, E. Ros et al.

In recent years, evidence has accumulated that some high-energy cosmic neutrinos can be associated with blazars. The strongest evidence for an individual association was found in the case of the blazar TXS 0506+056 in 2017. In July 2019, another track-like neutrino event (IC190730A) was found spatially coincident with the well-known bright flat-spectrum radio quasar PKS 1502+106. PKS 1502+106 was not found to be in a particularly elevated gamma-ray state, but exhibited a remarkably bright radio outburst at the time of the neutrino detection, similar to TXS 0506+056. We have performed a multi-frequency VLBI study from 15 GHz up to 86 GHz on TXS 0506+056, PKS 1502+106 and one additional neutrino-candidate blazar (PKS 0215+015) to study the radio structure of neutrino candidate blazars in response to their neutrino association. We have obtained target of opportunity observations with the VLBA for all three sources within ~1 month from their associated neutrino events and
are performing multi-epoch studies of the jet kinematics at 15 GHz as part of the MOJAVE program. Here, we present first results on TXS 0506+056 at 86 GHz and one additional 43 GHz image obtained 27 days after IC170922A, closer in time to the neutrino event than previously published images. We also give an overview about our recent work on PKS 1502+106 and PKS 0215+015.
 

30 June 2023

H. Müller, A. Mus & A.P. Lobanov

Context. Imaging in radioastronomy is an ill-posed inverse problem. However, with increasing sensitivity and capabilities of telescopes, several strategies have been developed in order to solve this challenging problem. In particular, novel algorithms have recently been proposed using (constrained) nonlinear optimization and Bayesian inference.
Aims. The Event Horizon Telescope (EHT) Collaboration convincingly investigated the fidelity of their image reconstructions with large surveys, solving the image reconstruction problem with different optimization parameters. This strategy faces a limitation for the existing methods when imaging active galactic nuclei: Large and expensive surveys solving the problem with different optimization parameters are time-consuming. We present a novel nonconvex, multiobjective optimization modeling approach that gives a different type of claim and may provide a pathway to overcome this limitation.
Methods. To this end, we use a multiobjective version of the genetic algorithm (GA): the Multiobjective Evolutionary Algorithm Based on Decomposition, or MOEA/D. The GA strategies explore the objective function by evolutionary operations to find the different local minima and to avoid becoming trapped in saddle points.
Results. First, we tested our algorithm (MOEA/D) using synthetic data based on the 2017 EHT array and a possible EHT plus next-generation EHT configuration. We successfully recover a fully evolved Pareto front of nondominated solutions for these examples. The Pareto front divides into clusters of image morphologies representing the full set of locally optimal solutions. We discuss approaches to find the most natural guess among these solutions and demonstrate its performance on synthetic data. Finally, we apply MOEA/D to observations of the black hole shadow in Messier 87 with the EHT data in 2017.
Conclusions. The MOEA/D is very flexible and faster than any other Bayesian method, and it explores more solutions than regularized maximum likelihood methods. We have written two papers to present this new algorithm. In the first, we explain the basic idea behind multiobjective optimization and MOEA/D, and we use MOEA/D to recover static images. In the second paper, we extend the algorithm to allow dynamic and (static and dynamic) polarimetric reconstructions.

24 May 2023

H. Müller & A.P. Lobanov

Context. Due to the limited number of antennas and the limited observation time, an array of antennas in very long baseline interfer-ometry (VLBI) often samples the Fourier domain only very sparsely. Powerful deconvolution algorithms are needed to compute a final image. Multiscale imaging approaches such as DoG-HiT have recently been developed to solve the VLBI imaging problem and show promising performance: they are fast, accurate, unbiased, and automatic.
Aims. We extend the multiscalar imaging approach to polarimetric imaging, to reconstructions of dynamically evolving sources, and finally to dynamic polarimetric reconstructions.
Methods. These extensions (mr-support imaging) utilize a multiscalar approach. The time-averaged Stokes I image was decomposed by a wavelet transform into single subbands. We used the set of statistically significant wavelet coefficients, the multiresolution support (mr-support), computed by DoG-HiT as a prior in a constrained minimization manner; we fitted the single-frame (polarimetric) observables by only varying the coefficients in the multiresolution support.
Results. The Event Horizon Telescope (EHT) is a VLBI array imaging supermassive black holes. We demonstrate on synthetic data that mr-support imaging offers ample regularization and is able to recover simple geometric dynamics at the horizon scale in a typical EHT setup. The approach is relatively lightweight, fast, and largely automatic and data driven. The ngEHT is a planned extension of the EHT designed to recover movies at the event horizon scales of a supermassive black hole. We benchmark the performance of mr-support imaging for the denser ngEHT configuration demonstrating the major improvements the additional ngEHT antennas will bring to dynamic polarimetric reconstructions.
Conclusions. Current and upcoming instruments offer the observational possibility to do polarimetric imaging of dynamically evolving structural patterns with the highest spatial and temporal resolution. State-of-the-art dynamic reconstruction methods can capture this motion with a range of temporal regularizers and priors. With this work, we add an additional simpler regularizer to the list: constraining the reconstruction to the multiresolution support.

 

26 April 2023

R.S. Lu, K. Asada, T.P. Krichbaum, et al.

The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of 8.4_−1.1^+0.5 Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects, in addition to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of the jet-launching region is wider than the expected profile of a black-hole-driven jet, suggesting the possible presence of a wind associated with the accretion flow.
 

28 February 2023

S.D. von Fellenberg, M. Janssen, J. Davelaar et al.

We report four novel position angle measurements of the core region M 81* at 5 GHz and 8 GHz, which confirm the presence of sinusoidal jet precession in the M 81 jet region, as suggested by Martí-Vidal et al. (2011, A&A, 533, A111). The model makes three testable predictions regarding the evolution of the jet precession, which we test in our data with observations from 2017, 2018, and 2019. Our data confirm a precession period of ∼7 yr on top of a small linear drift. We further show that two 8 GHz observation are consistent with a precession period of ∼7 yr but show a different time lag with respect to the 5 GHz and 1.7 GHz observations. We do not find a periodic modulation of the light curve with the jet precession and therefore rule out a Doppler nature for the historic 1998–2002 flare. Our observations are consistent with either a binary black hole origin for the precession or the Lense-Thirring effect.