Here we show recent research results from the Radio Astronomy/Very-Long-Baseline Interferometry department.
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.
The collimation in the twin jet of NGC 1052
09 February 2022
The radio galaxy NGC 1052 has been explored in the innermost regions of its dual jet by means of radio interferometr. An international team of radio astronomers led by Dr. Anne-Kathrin Baczko from our institut shows that the jet presents a clear transition in the collimation profile at 10 000 gravitational radii, with an upstream parabolic shape, which turns into conical downstream. At about 1 000 gravitational radii, the jet has an opening angle of about 30°. These results show that the approaching (eastern) and receding (western) show a somewhat different emission, for which the receding jet emission my be affected by an absorption cloud of gas in the line of sight. More information is available at the original publication in the journal Astronomy & Astrophysics, available here.
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.
EHT imaging of Centaurus A: A conversation with Nature Astronomy and Michael Janssen (and also the MPIfR alumni Sera Markoff and Marios Karouzos)
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.
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.
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.
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.
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
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.
The monster awakes: galaxy flares after years of silence
28 October 2020
The narrow-line Seyfert 1 galaxy Markarian 335 hosted a very bright X-ray active nucleus which faded since 2007. Observations from the Swift observatory led by S. Komossa at the MPI für Radioastronomie show a sequence of bright and rapid flare events in the X-ray band, after a long "quiet" time. The new activity in the source can be explained by a decrease of the amount of matter between the active nucleus and us, which partially covered the bright emission. The curtain is lifted, and it shows, the "monster" seems to be awake, but was always there. This work is published in the present issue of Astronomy & Astrophysics, see here.
After the footprints of stellar formation: isotope dating of the clouds to the Galactic Centre
23 October 2020
The present issue of the Astronomy & Astrophysical journal reports about spectral-line observations towards the Galactic centre clouds, in a project led by the PhD researcher Pedro Humire. This study shows a drop in the production of massive stars at the Galactic centre, based on measurements of the carbon and sulphur abundances in the interstellar medium. For that different isotopes int he CS molecule were studied (combinations of atomic weight values of 12 and 13 for carbon, and of 32, 33, and 34 for sulphur). Isotopic ratios can be computed for the different species, and the study shows that the decreasing trend in the 32S/34S ends at about 425 light-years from the centre of our galaxy. More details can be checked at the original publication, here.
The connection between gamma rays and radio emission in radio galaxies
23 September 2020
A work presented by R. Angioni from the MPI für Radioastronomie gives new clues on the connection between the low-energy (radio) and the high-energy (gamma) emission in radio galaxies. This is part of a larger work which is presented in a series of publications; the present report focus on prominent radio galaxies in the Southern hemisphere which were not detected by the Fermi/LAT telescope, and gives details on the jet kinematics for several objects. In general, the study shows that high-energy emission from radio galaxies is related to parsec-scale radio emission from the inner jet, but is not driven by relativistic Doppler boosting effects, in contrast to the situation in blazars. The results are presented in the last issue of Astronomy & Astrophysics, for more information see here.
The Wobbling Shadow of the M87* Black Hole
This animation presents about three years in the life of M87*, as predicted by numerical simulations. It shows the expected appearance and dynamics of the supermassive black hole as observed by the EHT. You can see turbulent gas heated to billions of degrees swirling around the event horizon, before finally plunging into the black hole. A sharp bright ring surrounding the black hole shadow is an effect of extremely strong lensing near the so-called photon shell.
The blurred portion of the animation corresponds to the effective resolution of the EHT. The dashed black ring measures 42 microarcseconds in diameter. The clock hand indicates the position of the bright side of the fitted crescent. We expect that the bright side should be most of the time located in the bottom of the image, where the velocity of the rotating gas is pointed in the observer’s direction. However, because of the turbulence, the fitted position angle varies quite a bit - the crescent wobbles. By studying the time-variability of the M87* image with the EHT, we can learn about the physics of matter in an extreme environment very near the event horizon, and understand the relations between the black hole and the accretion flow surrounding it.
Looking sharper, blobs become filaments: RadioAstron Observations of 0836+710
September 4, 2020
A new study published in the present issue of Astronomy & Astrophysics shows the striking improvement in resolution provided by the space-VLBI mission RadioAstron. The work is based in a study made in the framework of the PhD thesis of Laura Vega-García, performed at the MPI für Radioastronomie. The RadioAstron images reveal a wealth of structural detail in the jet of S5 0836+710 on angular scales ranging from 0.02 mas to 200 mas. Brightness temperatures in excess of 1013 K are measured in the jet, requiring Doppler factors of ≥100 for reconciling them with the inverse Compton limit. Furthermore, several oscillatory patterns are identified in the ridge line of the jet and can be explained in terms of the Kelvin–Helmholtz (KH) instability. For more information, check here.
Binary super massive black hole and jet activity in the quasar OJ 287
27 July 2020
A team of astronomers led by S. Komossa from the MPI für Radioastronomie has observed a very bright X-ray–UV–optical outburst of OJ 287 in 2020 April–June, the second brightest since late 2015. The outburst is predominantly powered by jet emission. The study reports evidence for reprocessing around the iron region in the source core, consistent with an absorption line. If confirmed, it implies matter in outflow at a tenth of speed light. The monitored source brigthness shows multiple episodes of flaring or dipping with a total amplitude of variability of one order of magnitude over the last four years prior to the 2020 outburst. This outburst is consistent with an after-flare predicted by a binary black hole model, where the disc impact of the secondary black hole triggers time-delayed accretion and jet activity of the primary black hole. This work is presented in the latest issue of the British journal Monthly Notices of the Royal Astronomical Society, see the publication here.
High-energy neutrinos originate in black-hole powered jets in active galactic nuclei
May 13, 2020
A team of astrophysicists including Yuri Y. Kovalev, affiliated to the MPI für Radioastronomie and Bessel Award of the Alexander von Humboldt foundation, have come close to solving the mystery of where high-energy neutrinos come from in space. The team compared the data on the elusive particles gathered by the Antarctic neutrino observatory IceCube and on long electromagnetic waves measured by radio telescopes. Cosmic neutrinos turned out to be linked to flares at the centers of distant active galaxies, which are believed to host supermassive black holes. As matter falls toward the black hole, some of it is accelerated and ejected into space, giving rise to neutrinos that then coast along through the universe at nearly the speed of light. These results are published in the last issue of The Astrophysical Journal, see the publication here, and a press release from the Moscow Institute of Physics and Technology here.
Jet shapes in active galactic nuclei dissected: changing from parabolic to conical shape and its physical implications
16 April 2020
A team of astronomers led by Yuri Y. Kovalev from Moscow (Lebedev & MIST), also associated to the MPI für Radioastronomie, has presented a work on ten active galactic nuclei in the close universe (redshift smaller than 0.07) displaying a transition from a parabolic to conical shape. They infer that the geometry transition may be a common effect in AGN jets, and observed only when sufficient linear resolution is obtained. This break occurs at distances of hundred thousand to one million gravitational radii from the nucleus. More in detail, this means that the jet shape transition happens when the bulk plasma kinetic energy flux becomes equal to the Poynting energy flux, while the ambient medium pressure is assumed to be governed by Bondi accretion. In general, the break point may not coincide with the Bondi radius. The results are presented in the online version of the journal Monthly Notices of the Royal Astronomical Society, available here.
EHT zoom into 3C 279 reveals inner structure and jet proper motions
Media coverage on 3C 279 Press Release (selection)
Located the site of emission of high-energy gamma rays in the blazar TXS 2013+370
17 February 2020
An international team of astronomers led by the doctoral researcher Efthalia Traianou from the MPI für Radioastronomie has identified the location of the gamma-ray emission in the blazar jet TXS 2013+370. The published results report very-long-interferometry observations of the blazar in the period 2002-13 at four wavelengths up to the challenging 3.5 mm addressed by the Global mm-VLBI Array (GMVA). The images revealed the existence of a spatially bent jet, described by co-existing moving emission features and stationary features. New jet features, lare observed to emerge from the core, accompanied by flaring activity in radio/mm- bands and γ-rays. The work infers that the high energy emission is produced at a distance of the order of about 3 lt-year from the jet apex, suggesting that the seed photon fields for the external Compton mechanism originate either in the dusty torus or in the broad-line region. These results are published in the present issue of the Astronomy & Astrophysics journal, see the original work here.
A wobbling jet with a two-year period
12 February 2020
The quasar PG 1553+113 is the first one showing an approximately two-year quasi-periodic pattern in its γ-ray light curve, which is also revealed at optical frequencies. A study by an international team of radio astronomers led by the MPIfR scientist Rocco Lico has analysed very-long-baseline interferometry observations of the source with a two-month cadence at three bands. The study shows a core-dominated source with a limb-brightened jet structure whose position angle varies in time in the range of 40° to 60°. The core region polarisation percentage varies in the range of a few percent, and the polarisation angle varies from being roughly parallel to roughly transverse to the jet axis. Although the jet wobbling motion indicates that geometrical effects can produce an enhanced emission through Doppler boosting modulation, additional mechanisms are required in order to account for the quasi-periodic variability patterns observed in γ-rays. Further details of this work are presented in the original publication at Astronomy & Astrophysics, see here.
Effelsberg observes methanol emission in nearby galaxies
17 January 2020
A team of astronomers led by the MPIfR PhD candidate Pedro Kumire has observed 36 GHz emission of methanol (CH3OH) in nearby galaxies using the Effelsbeg 100-m radio telescope. Emission was detected in Maffei 2 (at a distance of 19.6 million lt-yr) and IC 342 (at 11.4 million lt-yr) at 36 GHz (4−1 → 30 E transition), but not at 44 GHz transition. Upper limits were reported for M 82, NGC 4388, NGC 5278, and Arp 220. These results are published in Astronomy and Astrophysics, for more detail, check here.
The neutrino detection in the blazar TXS 0506+056, linked to superluminal expansion and limb brigthening in the sub-parsec scale of the source
2 January 2020
The first letter of the Astronomy & Astrophysical journal in the 2020s, led by Eduardo Ros of the MPIfR, reports on the rapid expansion of the centre of the blazar TXS 0506+056, based on millimetre VLBI observations performe with the VLBA. During the months after the neutrino event associated with this source, the overall flux density was showing a steady increase, happening solely within the core. Notably, the core expands in size with apparent superluminal velocity during these six months so that the brightness temperature drops by a factor of three despite the strong flux density increase. The radio jet of TXS 0506+056 shows strong signs of deceleration and/or a spine-sheath structure in the innermost region. This structure is consistent with theoretical models that attribute the neutrino and gamma-ray production to interactions of electrons and protons in the highly relativistic jet spine with external photons originating from a slower moving jet region. Proton loading due to jet-star interactions in the inner host galaxy is suggested as the possible cause of deceleration. Further details can be found in the original publication here.
The first image of a black hole, scientific highlight of 2019 and even of the 2010s
2 January 2020
The announcement and publication of the first image of a black hole in April 2019, with substantial contribution of the MPIfR and its Radio Astronomy/VLBI department, has been highlighted by different media as one of the major scientific discoveries of the last year and of the 2010s. Here we provide some of the links reporting this fact.
Predicting Cherenkov telescope detections from Active Galactic Nuclei
14 October 2019
The MPIfR astronomer Roberto Angioni publishes today at the journal Astroparticle Physics a study of the detection prospects for the Cherenkov Telescope Array (CTA). By simulating observations of forty-one γ-ray radio galaxies, extrapolating their Fermi-LAT spectrum into the TeV energy range assuming different spectral shapes, the author predicts that the CTA will detect eleven new TeV radio galaxies with an observational campaign of fifty hours per source. This would increase the sample of very-high-energy radio galaxies by a factor of three. More details, in the original publication here.
Gamma-ray emission at 140 light years from the jet base in the quasar 3C 279
23 September 2019
An international team of astronomers, led by Víctor M. Patiño-Álvarez, affiliated to the MPI für Radioastronomie and now leader of a partner research group at the Mexican Instituto Nacional de Astrofísica Óptica y Electrónica in Puebla has presented a study of the radio-gamma connection in the quasar 3C 279. A comparison of the flux variability in jet features with the gamma-ray variability suggests that the gamma-ray variability is correlated with a particular region downstream from the observed base of the jet at a distance of about 140 lt-yr. This feature shows an apparent superluminal velocity of about 3.7 times the speed of light, implying that one of the gamma-ray emission zones is not stationary. Further details can be found in the original publication at the Astronomy & Astrophysics journal here.
Event Horizon Telescope Collaboration Announces New Management Team
17 September 2019
Professor Anton Zensus, the Chairman of the Board of the Event Horizon Telescope Collaboration, announces the search for a new EHT director and changes to the EHT management, which become effective on September 17, 2019.
The US National Science Foundation has announced the funding of a $12.7M Mid-Scale research innovation grant (MSRI), to develop technologies and techniques that will help to create transformational capabilities for a next-generation Event Horizon Telescope array, envisaged for the second half of the 2020s. Shep Doeleman is PI of this award, and several other US institutions are participating.
“The development of long-term technologies and techniques is an important step towards taking the Event Horizon Telescope into the future. There are none more qualified to lead such a visionary effort than Shep, and we are looking forward to working with him over the coming months to help coordinate the MSRI activities with related work across the EHT collaboration” notes Anton Zensus.
The EHT Board recognizes Shep Doeleman as the Founding Director of the Event Horizon Telescope, acknowledging his leadership to the phenomenal success of the EHT, which led to the first image of a black hole in the galaxy Messier 87.
"The spectacular M87 EHT results have surpassed our wildest expectations, and I am deeply proud of what we achieved as a team. Now the question one hears the most is "what's next?", and the next-generation EHT initiative is the exciting clear response. I look forward to continuing to support the EHT, and am delighted to focus on this new direction." says Shep Doeleman, EHT Founding Director.
The Board will immediately initiate the search to fill the now vacant position of EHT Director, while supporting continuity of the activities of the project through a series of management changes.
* Mike Hecht, Associate Director at Haystack Observatory, will serve as Deputy Project Director;
* Geoff Bower of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), the vice Chair of the EHT Science Council, will serve as Project Scientist.
* Remo Tilanus of Leiden Observatory will serve as Operations Manager.
* David James of the Harvard-Smithsonian Center for Astrophysics will continue to provide project management support to the Team.
“The EHT Management Team is enhanced to address the evolving management and communication needs of our collaboration, which has seen rapid growth in membership, and increasing complexity in operations, scientific and development activities. Shep has graciously offered to continue to advise the Management Team during the transition period” adds Zensus.
Prof. Dr. J. Anton Zensus
Dr. Colin J. Lonsdale
Prof. Dr. Eduardo Ros
EHT Board Chairman
EHT Board Vice-Chairman
|EHT Board Executive Secretary|
MPI für Radioastronomie, Bonn, Germany
MIT Haystack Observatory, Westford, MA, USA
MPI für Radioastronomie, Bonn, Germany
Tel. +49 228 525 378
Tel. +1 617 715 5575
Tel. +49 228 525 125
A Test of General Relativity at The Galactic Center
25 July 2019
In a detailed study of a star orbiting the supermassive black hole at the center of our Galaxy, researchers report that Einstein’s theory of general relativity (GR) accurately describes motion around this massive structure. Tuan Do, Andrea Ghez and their colleagues including Gunther Witzel from the Max Planck Institute for Radio Astronomy in Bonn, Germany, report novel spectral data and expanded analyses. The findings are presented in this week’s issue of the magazine „Science“ (UCLA Press Release, 25 July 2019). [more]
Gamma-ray emission in radio galaxies under the VLBI scope
15 July 2019
The POLAMI Collaboration has published a study, led by the MPI für Radioastronomie researcher R. Angioni, of the gamma-ray emission of Southern radio galaxies. These results are published in the last issue of the Astronomy & Astronomy journal. The study shows that the brightness of the core of the radio sources correlates with the gamma-ray emission, as seen in blazars. However, the gamma-ray luminosity does not show dependence with the compact radio emission of the core of the galaxies, which is a common indicator of Doppler boosting. The authors conclude that the gamma-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, according with the unified model of jetted active galactic nuclei. More information is available here.
The large gamma-ray flare of the flat-spectrum radio quasar PKS 0346−27
12 July 2019
A multi-messenger study led by R. Angioni of the MPI für Radioastronomie, published in the present issue of Astronomy & Astrophysics, reports on the long- and short-term flux and spectral variability from the radio quasar PKS 0346−27, producing gamma-ray light curves with different time binning. Evidence of short-time scale variability down to 90 min is presented. The source shows remarkable properties during an outburst in May 2018, and is a promising target for future ground-based Cherenkov observatories. More information is available at the original publication here.
The gamma-loud radio galaxy 3C 264
4 July 2019
A team of astronomers led by the astronomer B. Boccardi of the MPI für Radioastronomie publishes in the latest issue of Astronomy & Astrophysics a high-resolution radio study of the gamma-ray emitting galaxy 3C 84. The authors present a adio and X-ray analysis of the jet in 3C 264. They determine the main physical parameters of the parsec-scale flow and explore the implications of the inferred kinematic structure for radiative models of this γ-ray emitting jet. The publication suggests that the high-energy emitting region is located at the end of the acceleration zone of the jet, either in the jet layer or in the spine. Further information can be found here.
A study of the physics of the complex jet in the blazar S5 0836+710
3 July 2019
The last issue of the journal Astronomy & Astrophysics reports the results of a thorough analysis of the jet profile of the high-resolution images of the blazar S5 0836+710. The study is led by the MPI für Radioastronomie researcher L. Vega García. The authors ran numerical calculations of stability of a relativistic, sheared jet over a range of different jet parameters, based on the assumption that the observed structures are generated by growing Kelvin–Helmholtz instability modes. The results yield physical parameters of the jet, with a Lorentz factor of 12 and an internal Mach number of 12, as well as a jet-to-ambient medium density of 1/1000. More details can be found in the original publication here.
Media coverage (selection): Astronomers capture the first image of a black hole
Radio, television, internet movies, and podcasts
Twin, but asymmetric jets in the radio galaxy NGC 1052
26 February 2019
A study of twenty-nine observations using very-long-baseline interferometry in the radio galaxy NGC 1052, led by the MPIfR PhD student Anne-Kathrin Baczko, has revealed new details of the nature of the twin jet in this object. Interestingly, the approaching (eastern) jet has higher kinetic energy, whereas the receding (western) jet has a larger internal energy or magnetic flux. The inner structure of the jet can be explained by a spine-sheath with a fast inner layer and a slower outer layer. These results are published in the present issue of the Astronomy & Astrophysics journal, for the original publication, see here.
Resolving the innermost region of the radio galaxy NGC 1275 with mm-VLBI
19 February 2019
Using the Global mm-VLBI Array, an international team of astronomers led by J.Y. Kim from the MPI für Radioastronomie, has analysed the inner polarised structure of the nearby radio galaxy 3C 84 (NGC 1257), reaching resolutions of 50 μas (corresponding to ∼200 schwarzschild radii). The results suggest that the emission is associated with an underlying limb-brightened jet. The images match in resolution the ones obtained with space VLBI in our group, several months ago (see below). These results are published in the present issue of the journal Astronomy & Astrophysics, for the original publication, see here.
Helical magnetic fields and a recollimation shock in the classical quasar CTA 102
12 February 2019
The popular radio source CTA 102 (see the song by the Californian band The Byrds from 1967) continues being the object of study of radio astronomers. A new publication apppeared today, led by the MPIfR astronomer Carolina Casadio, reports on the magnetic field configuration and the interaction between traveling shocks and a recollimation shock in its relativistic jet. The study is based on observations at the wavelengths of 3.5 mm and 7 mm performed in the mid 2010s. A Faraday rotation analysis shows a gradient in the jet and intrinsic electric vector position angles oriented around the centroid of the innermost jet feature (core), suggesting the presence of large-scale helical magnetic fields. Monitoring shows a feature moving superluminally and crossing the core (central, brightest) region. The polarisation orientation is different when the mentioned feature is exiting the core or crossing a stationary feature. The interaction between the superluminal component and a recollimation shock could have triggered the multi-wavelength flares. The variability Doppler factor associated with such an interaction is large enough to explain the high-energy emission and the remarkable optical flare occurred very close in time. Further details on this work can be found at the original publication, see here.
New Global Millimetre VLBI Array Survey released
01 February 2021
The new survey of the GMVA, led by Dhanya G. Nair at the MPI für Radioastronomie, has been released, simultaneously to the corresponding publication at the present issue of the Astronomy & Astrophysics journal. The survey target source list has been compiled from the MOJAVE (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) sample, using the following selection criteria:
|a)||15 GHz correlated flux density, Sc ≥ 0.5 Jy on baselines of ≥ 400 Mλ;|
|b)||compactness at longest spacings, Sc /SVLBA ≥ 0.4 where S VLBA is the 15 GHz total clean flux density;|
|c)||declination δ ≥ 15°.|
With these selection criteria, a total of 162 unique sources have been selected, comprising 89 quasars, 26 BL Lac objects, 22 radio galaxies and 25 unidentified sources. For further details, please visit the dedicated webpage. Images can be downloaded here.
Helical magnetic fields in the bent jet of the quasar OJ 287
November 12, 2018
Deep in the heart of M 87
September 12, 2018
A new publication led by MPIfR astronomers (see here) presents Global mm-VLBI Array (GMVA) observations at 3.5 mm wavelength of the nearby radio galaxy Messier 87, the central galaxy of the Virgo cluster in a distance of about 50 million light years. The highlight image shows the central region of M 87 at an angular resolution of ~50 μas (7 Schwarzschild radii).
The imaging reveals a parabolically expanding limb-brightened jet which emanates from a resolved VLBI core of about ten Schwarzschild radii in size. The observed brightness and compactness of the central feature suggests magnetic energy dominance at the jet base. Data yield an estimate the diameter of the jet at its base to be about five Schwarzschild radii assuming a self-similar jet structure. This suggests that the sheath of the jet may be anchored in the very inner portion of the accretion disk. Combined images reveal faint emission at the center of the edge-brightened jet on scales smaller than light years.
Charge in the hole
August 12, 2018
Black holes have mass, angular momentum and potentially a charge. While the first two were measured routinely for some time now, constraining a black hole’s charge is more difficult. A comment by Marios Karouzos in "Nature Astronomy" refers to an original paper by MPIfR authors led by Michal Zajaček in MNRAS, proposing an observational way to test limits on the charge of Sgr A*, the black hole at the centre of the Milky Way. The original publication is available here.
Extreme outflows in radio-loud narrow-line Seyfert 1 galaxies
April 17, 2018
A team of astronomers led by Stefanie Komossa from the MPI für Radioastronomie in Bonn has studied four narrow-line Seyfert 1 galaxies and discovered extremely shifted spectral lines in their spectra, which indicate gas flying away from the central regions at speeds as high as 2450 km/s. These galaxies are also emitteres in the radio part of the electromagnetic spectrum. These results suggest that those galaxies are relatively young (in astronomical terms) with lifetimes of the order of magnitude of a million year. The results are published in the present issue of the journal Monthly Notices of the Royal Astronomical Society, to be found here.