Research Highlights

Here we show recent research results from the Radio Astronomy/Very-Long-Baseline Interferometry department.

Computing polarised jet emission

15 December 2021

A publication presented by Joana A. Kramer, PhD candidate at the MPIfR together with her supervisor, Nicholas R. Macdonald, shows that jet emission is edge-brightened when the magnetic field is toroidal in nature and spine-brightened when the magnetic field is poloidal in nature.  Additionally, the circularly polarized emission exhibits both negative and positive sign for the toroidal magnetic field morphology. Last but not least, the relativistic jet's emission is largely independent of different emission scaling relations when the ambient medium is excluded.  This is based in numerical simulations performed in 3D including relativistic,  magnetohydrodynamic effects (PLUTO code), and synthetic images created from these virtual jets (using the RADMC-3D code, which can reproduce the polarised emission of light coming from its energetic, black-hole-powered plasma.  More details are available in the present issue of Astronomy & Astrophysics, at this publication.

Into the Dark Heart of Centaurus A
Event Horizon Telescope exposes the center of the nearest radio galaxy more

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<span>This video Q&amp;A discusses the findings in the upcoming Nature Astronomy paper, 'Event Horizon Telescope observations of the jet launching and collimation in Centaurus A,</span>

EHT imaging of Centaurus A: A conversation with Nature Astronomy and Michael Janssen (and also the MPIfR alumni Sera Markoff and Marios Karouzos)

This video Q&A discusses the findings in the upcoming Nature Astronomy paper, 'Event Horizon Telescope observations of the jet launching and collimation in Centaurus A,
Jets Pose Many Riddles
14 July 2021

The super-energetic jets that shoot out of black holes are in the focus of a new DFG research group. The researchers are being funded with 3.6 million euros.  The MPIfR is involved in two sub-projects: Bia Boccardi and J. Anton Zensus lead the sub-project 
mm-VLBI studies of gamma-ray bright radio galaxies”, and J. Anton Zensus and Eduardo Ros participate at the sub-project led by Matthias Kadler and Christian M. Fromm in Würzburg, with title Jet physics one event horizon scales and beyond. more

The cosmic battery powers galaxy halo magnetic fields

20 May 2021

A publication by the MPIfR-affiliated astronomer Ioannis Myserlis and his colleague Ioannis Contopoulos (Athens) reveals, appeared today at the Astronomy & Astrophysics journal, postulates a universal mechanism to explain the magnetic fields in galactic halos.  The author have studied thirty-five nearby edge-on spiral galaxies from the Extended Very Long Array Survey named Continuum HAlos in Nearby Galaxies – an EVLA Survey (CHANG-ES), and detected large-scale magnetic fields in sixteen of them. The authors used radio polarization data to create Faraday rotation measure maps for all galaxies in the sample and stack them with the aim of amplifying any underlying universal toroidal magnetic field pattern in the halo above and below the disk of the galaxy.  The presented work discovered a large-scale magnetic field in the central region of the stacked galaxy profile, which is attributable to an axial electric current that universally outflows from the center, both above and below the plane of the disk. A similar symmetry-breaking has also been observed in astrophysical jets, but never before in galaxy halos. This is an indication that galaxy halo magnetic fields are probably not generated by pure magnetohydrodynamic processes in the central regions of galaxies. One such promising physical mechanism is the Cosmic Battery operating in the innermost accretion disk around the central supermassive black hole. More details of this work can be found in the original publication here.

Einstein's Theory Can Explain the Black Hole M87*

20 May 2021

Event Horizon Telescope Collaboration scientists including MPIfR researchers use data which produced the first image of a black hole to constrain its fundamental properties.

In 2019, the EHT Collaboration published the first image of a black hole located at the centre of the galaxy M87. Now a collaboration team led by theoretical physicists at the Goethe University Frankfurt and with the participation of the MPIfR EHT team have analysed data from the black hole M87* to test Albert Einstein's theory of general relativity. According to the tests, the size of the shadow from M87* is in excellent agreement with a black hole predicted by general relativity, but narrows the properties of black holes in other theories down. These results are presented in today’s issue of the Physical Review D journal.

Constraining black hole models with EHT observations | Event Horizon Telescope

X-ray studies from the binary black hole candidate OJ 287

05 May 2021

A new study of the quasar OJ 287, led by the MPI für Radioastronomie scientist Stefanie Komossa, presents results from spectroscopic observations performed between 2005 and 2020.  In the long period of study, the galaxy nucleus presents extreme activity minima and outbursts.  The X-ray spectrum of the source can be decomposed into three components: low-state emission consisting by Inverse Compton photons, super-soft synchrotron emission becoming dominant as the source brightens, and an additional outburst component with intermediately-soft photons.  The publication discuss in detail the postulated black hole binary nature (having the primary black hole a mass of 18 billion solar masses) of the central region and the X-ray results.  More details can be found at the original publication, presented at the latest issue of Monthly Notices of the Royal Astronomical Society.

Black holes as magnetic jet engines
European Research Council supports Bonn astrophysicists with 2.5 million euros to explain the phenomenon more

Challenging the radio galaxy classification with the VLA-COSMOS survey at 10 cm wavelength

20 April 2021

An international team of astronomers led by Eleni Vardoulaki (affiliated to the MPI für Radioastronomie, at present at the Thüringer Landessternwarte in Tautenburg) has studied a sample of faint radio galaxies down to μJy levels with the 15-GHz sample of the VLA-COSMOS survey.  Radio active galactic nuclei (AGN) are traditionally separated into two Fanaroff-Riley (FR) type classes, edge-brightened FRII sources or edge-darkened FRI sources. This dichotomy is becoming too simplistic in linking the radio structure to the physical properties of radio AGN, their hosts, and their environment.  The work by Vardoulaki and collaborators approached the study of these galaxies both measured by a machine-learning algorithm and also by hand, following a parametric approach to the FR classification. Different physical parameters were estimated, as well as the galaxy host properties.  The work shows a broad distribution and overlap of Fanaroff-Riley radio galaxies and jet-less/compact radio active galactic nuclei populations.  The results point to the need for a different classification scheme, that expands the classic  classification by taking into consideration the physical properties of the objects rather than their projected radio structure which is frequency-, sensitivity- and resolution-dependent. 

These results are presented in the last issue of the journal Astronomy & Astrophysics, see the original publication here.

RadioAstron reveals the complex structure in the jet of quasar 3C 345

14 April 2021

A team of radio astronomers led by the MPIfR astrophysicist Felix M. Pötzl has studied the innermost jet morphology and magnetic field strength in the active galactic nucleus (AGN) 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron.  The results analyze images obtained at a wavelength of 21 cm on 2016 March 30 with RadioAstron and eighteen ground-based radio telescopes.  The obtained images reveal a complex jet structure a resolution corresponding to a projected linear scale of about 2 pc or a few thousand gravitational radii.  This work identfies the synchrotron self-absorbed core at the jet base and find a brightest feature in the jet several parsecs downstream of the core.  The work also studies the linearly polarised emission, which is related to the magnetic field distribution in the jet, and the intrinsic brightness of the source and its information about the source physics (via the so-called brightness temperature).

Additional information can be obtained at the original publication here.

Multifrequency Observations of M87*
Telescopes unite in unprecedented observations of the famous black hole more
<p>Beginning with the EHT’s now iconic image of M87, a new video takes viewers on a journey through the data from each telescope. Each step provides data across many factors of ten in scale, both of wavelengths of light and physical size.</p>

Zoom Out of the Black Hole M87*

Beginning with the EHT’s now iconic image of M87, a new video takes viewers on a journey through the data from each telescope. Each step provides data across many factors of ten in scale, both of wavelengths of light and physical size.

Event Horizon Telescope 2021
Observing campaign in April 2021: world-wide radio telescope network retakes observations after 3-year long break more
The Opticon-RadioNet Pilot Project (ORP) is launched
Kick-off for Europe’s largest astronomy network more

A swing in the jet direction at the quasar 3C 273

24 March 2021

The high-redshift radio source with number 273 in the third Cambridge catalog (also known as 4C +02.32, ON 044, or CTA 053) is one of the best studied objects in very-long-baseline interferometry.  New results presented in a publication led by the Bonn astronomer Misha Lisakov reveals changes in the polarisation of the jet which suggest a change in the jet direction during the period 2009-2010 from multi-wavelength studies using the Very Long Baseline Array.  The work, presented in the latest issue of The Astrophysical Journal, shows that the jet Faraday rotation measure has changed significantly toward negative values compared with that previously observed. These changes could be explained by a swing of the parsec-scale jet direction, which causes synchrotron emission to pass through different portions of the Faraday screen. The work develops a model for the jet-sheath system in 3C 273 where the sheath is wider than the single-epoch narrow relativistic jet.  The wide jet–sheath boundary is about 750 light years downstream from its beginning. Most of the Faraday rotation occurs within the innermost layers of the sheath.   Further details on the jet parameters and the impact of this work in the study of other sources can be obtained in the original publication, see here.

EHT Astronomers Image Magnetic Fields at the Edge of M 87’s Black Hole
The EHT has imaged the polarised emission of the ring around the black hole shadow in Messier 87.  The polarimetry working group of the collaboration, mostly responsible of this result, is coordinated by Iván Martí-Vidal (Univ. València, alumnus of the MPIfR) and Monika Mościbrodzka (Radboud Univ.); additionally Jason Dexter (Univ. Colorado Boulder, alumnus of the MPI for extraterrestrial Physics) and Andrew Chael (Princeton) coordinated the theory part of the work. more

Zoom into the Magnetized Black Hole M87* | Event Horizon Telescope

The Black Hole M87* Seen Through a Polarizer | Event Horizon Telescope

What is Polarization? | Event Horizon Telescope

How Magnetic Fields Affect Black Hole Images | Event Horizon Telescope

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A ring accelerator to produce neutrinos in a quasar jet?

17 March 2021

An international team of radio astronomers led by Silke Britzen at the MPI für Radioastronomie suggests the connection between the high-energy neutrino production in the quasar PKS 1502+106 with remarkable features in the jet.  Their analysis suggests a radio ring structure in the parsec-scale jet that develops with time. Several arc-structures evolve perpendicular to the jet ridge line. The work also finds hints for precession of a curved jet based on kinematic modelling and a periodicity analysis.  The atypical ring may be connected to an interaction of the precessing jet with the outflowing material.  Energetic neutrinos are most likely produced by proton–proton interaction in the blazar zone, enabled by episodic encounters of the jet with dense clouds, that is, with some molecular cloud in the outer part.  These results have been published today for the May 2021 issue of the British journal Monthly Notices of the Royal Astronomical Society.  For additional information, see here

Collimating jets in radio galaxies: the case of NGC 315

11 March 2021

A study presented by a European team led by the MPIfR astronomer Bia Boccardi (head of an Otto Hahn Research Group) today in Astronomy and Astrophysics reveals a zoom in the structure of the powerful jets in this radio galaxy.  The double jet in this galaxy shows a remarkable persistence in its direction at very different scales.  The collimation, apparently, is already completed in the innermost region (parabolic shape) and is kept for scales much larger than the optical galaxy (conical shape). 

The optical nebula hosting the powerful jet has the number 315 in the New General Catalogue (NGC 315).  It is an elliptical galaxy in the constellation Pisces.  It was discovered on September 11, 1784 by William Herschel.  It is also known as HOLM 028A, OB +392, and TXS 0055+300.

Furthermore, Boccardi's work discusses the possibility that relativistic jets are collimated by winds originated by the accretion disk which surrounds the super massive black hole.  The study suggests that a powerful external layer in the jets (sheath) stabilizes the inner spine by isolating it from the interstellar medium, so that the jet travels mostly unperturbed to reach the intergalactic medium.  These considerations also play a role to define the different types of galaxy, classified as type I (luminosity decreases as the distance from the central galaxy or quasar host increase) or type II (increasing luminosity in the lobes) in 1974.  The publication (open access) can be found here.

Honour for the Event Horizon Telescope (EHT)
The 2021 Royal Astronomical Society Group Achievement Award goes to the EHT Project more
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