Here we show recent research results from the Radio Astronomy/Very-Long-Baseline Interferometry department.
A novel multiscale imaging approach for radio interferometry: DoG-HiT
19 October 2022
A new algorithm for imaging interferometric data has been developed by MPIfR astronomers Hendrik Müller and Andrei P. Lobanov, based on a multiscale wavelet deconvolution algorithm, DoG-HiT, for imaging sparsely sampled interferometric data. The method combines the difference of Gaussian (DoG) wavelets and hard image thresholding (HiT). DoG-HiT is a stable method and benchmark its performance against image reconstructions made with the CLEAN and regularized maximum-likelihood (RML) methods using synthetic data. The comparison shows that DoG-HiT matches the super-resolution achieved by the RML reconstructions and surpasses the sensitivity to extended emission reached by CLEAN. Further details of this algorithm can be found the publication presented in the latest issue of Astronomy & Astrophysics, available here.
A comprehensive summary of the VLBI analysis software, presented to the community
10 October 2022
Very-long-baseline interferometry (VLBI) is a challenging observational technique, which requires in-depth knowledge about radio telescope instrumentation, interferometry, and the handling of noisy data. The reduction in raw data is mostly left to the scientists and demands the use of complex algorithms implemented in comprehensive software packages. The correct application of these algorithms necessitates a good understanding of the underlying techniques and physics that are at play. The verification of the processed data produced by the algorithms demands a thorough understanding of the underlying interferometric VLBI measurements. A review led by MPIfR scientist Michael Janßen, also contributed by Jan Wagner from our institute describes the latest techniques and algorithms that scientists should know about when analyzing VLBI data. This work is published in the present issue of the scientific journal Galaxies, see here.
Unlocking the secrets of 3C 84's powerful jet
31 August 2022
An international team of scientists led by Georgios F. Paraschos from the MPI für Radioastronomie has studied the radio galaxy 3C 84 for over two decades to understand its powerful jets. By using advanced telescopes, researchers were able to produce high-resolution images of the jet's inner core region and determine the kinematics of its ejected features. They found that the jet features travel at speeds between 0.055 and 0.22 times the speed of light and their ejection times coincide with changes in radio and gamma-ray emissions. The scientists also discovered that the jet's width varies with frequency, which suggests that it has a stratified structure. The findings provide insights into the jet's origin and how it evolves over time.
More information, at the publication in the present issue of the Astronomy & Astrophysics journal, here.
How is giant radio galaxy NGC 315's accretion disk powering Its jet?
26 August 2022
A team of astronomers led by Luca Ricci from the MPI für Radioastronomie has studied the properties of a giant radio galaxy, NGC 315, to better understand how the jets seen in active galactic nuclei are powered. Astronomers looked at data from different time periods and frequencies to analyze the source maps and used theoretical models to link the properties of the jet to the physical state of the accretion disk. We found that the bulk flow in NGC 315 accelerates on sub-parsec scales, and this fast acceleration can be explained by magnetism. They also observed a region with a very steep spectral behavior, which indicates that the black hole of NGC 315 is rotating fast and the magnetic flux threading the accretion disk is in excellent agreement with that expected in the case of a magnetically arrested disk (MAD). Using a new technique, they modeled the magnetic field downstream of a quasi-parabolic accelerating jet and reconstructed it up to the event horizon radius. In the MAD scenario, we compared it with the expected magnetic saturation strengths in the disk, finding a good agreement.
More information, at the present issue of the Astronomy & Astrophysics journal, here.
A closer look at the young stars at the galactic center
May 12, 2022
A work led by the MPIfR scientist Maciek Wielgus shows how umerical simulations of accretion discs around a stellar-mass black hole reveal their stratified, elevated vertical structure.These are referred as puffy discs. The work discusses the observational properties of puffy discs, particularly the geometrical obscuration of the inner disc by the elevated puffy region at higher observing inclinations, and collimation of the radiation along the accretion disc spin axis, which may explain the apparent super-Eddington luminosity of some X-ray objects. Synthetic spectra are presented, showing that they are qualitatively similar to those of a Comptonized thin disc. The work suggests that puffy discs may correspond to X-ray binary systems of luminosities above one third of the Eddington luminosity in the intermediate spectral states. The results are published in the present issues of the journal Monthly Notices of the Royal Astronomiccal Society, for more information see here.
EHT Image of the Black Hole in SgrA* - MPIfR scientists tell the story
This time we have insight information, emotional thoughts, and exciting scientific news collected by the Event Horizon Telescope (EHT) Collaboration members at the Max Planck Institute for Radio Astronomy in Bonn, Germany. It has been a great, devoting journey since Sagittarius A* was observed by the EHT in 2017. Our colleagues tell their side of the story.
Created by Joana A. Kramer & Luca Ricci, MPI für Radiastronomie
Press Conference at ESO on new Milky Way results from the EHT team, followed by a public Q&A event
The ESO Director General delivered the opening words. EHT Project Director Huib Jan van Langevelde and EHT Collaboration Board Founding Chair Anton Zensus delivered remarks. A panel of EHT researchers including Thomas P. Krichbaum (MPIfR) and Christian Fromm (Univ. Würzburg, also affiliated with the MPIfR) explained the result and answer questions from journalists.
Following the press conference, at 16:30 CEST ESO hosted an online event for the public via this same streaming link: a live question and answer session where members of the public will have the opportunity to query another panel of EHT experts (which include also Michael Janssen from the MPIfR).
Selected press coverage
For the German-speaking reporting, go to our area in German language.