Contact

Prof. Dr. J. Anton Zensus

Director and Head of the Research Department
"Radio Astronomy/VLBI"

Phone: +49 228 525-298 (Secretary)

https://antonzensus.mpifr-bonn.mpg.de

Director's blog feed

GMVA Survey

GMVA Survey of Ultracompact Extragalactic Radio Sources

Database of the Global mm-VLBI Array Survey of Extragalactic Radio Sources (Nair et al., A&A 622, A92, 2019)

Radio Astronomy / VLBI

Header image 1433748789

Radio Astronomy / VLBI

mm-VLBI in our scientific and technology divisions

Millimetre very-long-baseline interferometry at the Max Planck Institute for Radio Astronomy

The Max Planck Institute for Radio Astronomy in Bonn (Germany) is one of the key players in the Event Horizon Telescope (EHT) collaboration. The team led by J. Anton Zensus played a crucial role in the discovery of the Black Hole in M87. The movie describes the work and achievements of the group in the field of mm VLBI: from observational and technological challenges until the break through scientific discoveries.

Breakthrough discovery in astronomy: first ever image of a black hole - Press Conference at the European Commission on April 10, 2019

On 10 April 2019 at 15:00 CEST (Bonn time) the European Commission presented a ground-breaking discovery by Event Horizon Telescope - an international scientific collaboration aiming to capture the first image of a black hole by creating a virtual Earth-sized telescope. EU-funded researchers play a key role in the project.

Black holes are extremely compressed cosmic objects, containing incredible amounts of mass within a tiny region. Their presence affects their surroundings in extreme ways, by warping spacetime and super-heating any material falling into it. The captured image reveals the black hole at the centre of Messier 87, a massive galaxy in the constellation of Virgo. This black hole is located 55 million light-years from Earth and has a mass 6.5-billion times larger than our sun.

Six press conferences around the world took place simultaneously. In Europe, Commissioner Moedas and lead scientists funded by the European Research Council held a press conference in Brussels to unveil the discovery.

Panelists:
- Carlos Moedas, European Commissioner for Research, Science and Innovation
- Prof. Anton Zensus, Director at Max-Planck-Institut für Radioastronomie, Bonn, Germany (Chair of the EHT Collaboration Board)
- Prof. Heino Falcke, Radboud University, Nijmegen, The Netherlands (Chair of the EHT Science Council)
- Dr Monika Mościbrodzka, Radboud University, Nijmegen, The Netherlands (EHT Working Group Coordinator)
- Prof. Luciano Rezzolla, Goethe Universität, Frankfurt, Germany (EHT Board Member)
- Prof. Eduardo Ros, Max-Planck-Institut für Radioastronomie, Bonn, Germany, (EHT Board Secretary)
MPIfR and IRAM contribute to groundbreaking observations of the gargantuan black hole at the heart of distant galaxy Messier 87

MPIfR official press release: Astronomers Capture First Image of a Black Hole

April 10, 2019

MPIfR and IRAM contribute to groundbreaking observations of the gargantuan black hole at the heart of distant galaxy Messier 87 [more]

The picture: Shadow of the Black Hole in M 87

The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the centre of Messier 87 and its shadow.
The shadow of a black hole seen here is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon.
Although the telescopes making up the EHT are not physically connected, they are able to synchronize their recorded data with atomic clocks — hydrogen masers — which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global campaign. Each telescope of the EHT produced enormous amounts of data – roughly 350 terabytes per day – which was stored on high-performance helium-filled hard drives. These data were flown to highly specialised supercomputers — known as correlators — at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration. Zoom Image

The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the centre of Messier 87 and its shadow.

The shadow of a black hole seen here is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon.

Although the telescopes making up the EHT are not physically connected, they are able to synchronize their recorded data with atomic clocks — hydrogen masers — which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global campaign. Each telescope of the EHT produced enormous amounts of data – roughly 350 terabytes per day – which was stored on high-performance helium-filled hard drives. These data were flown to highly specialised supercomputers — known as correlators — at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration.

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Radio Astronomy/VLBI Department: Overview

By employing radio-interferometry, extragalactic objects and their centres are investigated in great detail. The Very Long Base Line Interferometry (VLBI) technique is applied by correlating data from telescopes distributed worldwide and using them as a “giant“ combined telescope within the framework of coordinated arrays as the the European VLBI network (EVN). In addition, global VLBI experiments are conducted in cooperation with telescopes in the USA.

Compact radio sources are the astronomical 'target' in our studies.  Thanks to the expertise over decades our group in radio interferometric techniques our department counts among the world leading groups in this area.

Our main research topics focus in the investigation of Active Galactic Nuclei (AGN) and their emission.  The emission has a non-thermal nature and is rapidly variable.  AGN show strong plasma outflows originating near a central, massive black hole.  These so-called jets, emit synchrotron radio light.  AGN have intrinsically two-sided jets, but usually only one of them is seen, due to relativistic effects (Doppler boosting).  AGN jets also display the intriguing phenomenon of superluminal motion.  Blazars are the small fraction of those AGN with jets pointing towards the observer.  The key physical concepts involve jet launching, opacity effects in the ‘core’ near the jet base, and the propagation of shocks in the jets and energy dissipation.

Stacked image of the quasar CTA102, from the MOJAVE project
  Zoom Image
Stacked image of the quasar CTA102, from the MOJAVE project
 

Main Research Topics

The group research can be summarised in three main areas: very-high-resolution imaging of compact radio sources, VLBI monitoring of milliarcsecond-scale structural changes, and spectral and polarisation monitoring of radio sources.  A series of additional projects and initatives rounds the scientific portfolio of the VLBI department.

Very-high-resolution imaging

The MPIfR leads efforts at high resolutions in two directions: using the shortest possible wavelengths to overcome overcome further the opacity barrier of synchrotron self-absorption in AGN, and extending VLBI to baseline lengths larger than the Earth size with radio telescopes in space.

Space-VLBI Image of the BL Lac Object 0716+714 Zoom Image
Space-VLBI Image of the BL Lac Object 0716+714

Space-VLBI: Ground-space VLBI provides an alternative way of increasing resolution in radio interferometry.  The Russian RadioAstron  project successfully launched a 10-m radio telescope, Spektr-R, in July 2011.  With a perigee of 10,000 km and an apogee of 399,000 km, angular resolution down to a few microarcseconds are possible.  Available wavelengths are 92, 18, 6, and 1.3 cm.  Our group is involved on several Key Science Programs of this collaboration, leading 3 (out of 8) of these.  The VLBI Technology Division is involved in the correlation of ground-RadioAstron data with the MPIfR DiFX software correlator.

Simulation of onset of jet near black hole Zoom Image
Simulation of onset of jet near black hole

mm-VLBI: The MPIfR leads the operation of the Global mm-VLBI Array (GMVA), which combines European mm-telescopes (Effelsberg, Pico Veleta, Plateau de Bure, Onsala, Metsähovi) with the Very Long Baseline Array in the USA to provide a 3-mm imaging capability with 50 microarcsecond resolution.  The network has prospects of future participation with additional mm-telescopes such as the ones of the Korean VLBI Network. 

VLBI at 1.3mm constitutes the next logical (and challenging) step for higher angular resolution and to overcome further the opacity barrier of synchrotron self-absorption in AGN and to open a direct view into sub-parsec scale regions not previously accessible.  The so-called Event Horizon Telescope (EHT) has the goal of imaging the shadow of the black hole in the Galactic Centre at this wavelength.  The high technological approach requires the participation of the VLBI Technology division.

VLBI monitoring of milliarsecond-scale structural changes

TANAMI view of Centaurus A Zoom Image
TANAMI view of Centaurus A
 

MOJAVE: The project MOJAVE (Monitoring of Jets in AGN with VLBA Experiments) is an extensive VLBA monitoring survey aimed at studying the evolution and magnetic field structure of parsec-scale jets in blazars at 15 GHz.  MPIfR scientists are major participants in this NRAO key science program. Most of the jets in the MOJAVE project have been monitored since the mid-1990s providing a unique opportunity to study their long-term behaviour including accelerations, bending, and development of instabilities in jets.  Several multi-frequency experiments yield Faraday rotation measures, frequency-dependent core-shifts and spectral index maps for a subset of sources.

TANAMI:  The project TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) is a younger brother of the MOJAVE program, to provide dual-frequency (8 and 22 GHz) monitoring of extragalactic jets south of −30° declination.  The array comprises the Australian Long Baseline Array and telescopes in South Africa (Hartebeesthoek), Antarctica (O’Higgins) and Chile (TIGO), and new sites in New Zealand are joining the array.

Spectral and Polarisation Monitoring

F-GAMMA

The F-GAMMA program (Fermi-Gamma-ray space telescope AGN Multi-frequency Monitoring Alliance) is run by a MPIfR-lead consortium of scientific groups and observatories, to collect high-precision broad-band flux density and polarisation data for a large number of gamma-ray loud AGN in the ‘low-energy’ synchrotron part of blazar spectral energy distributions.  The alliance includes the Effelsberg 100-m, Pico Veleta 30-m and the APEX 12-m telescope for 0.8 mm band observations.

ROBOPOL

ROBOPOL is a project to build an optical polarimeter for a systematic study of the large swings of optical polarisation angle, often seen during high-energy outbursts of blazars.  Those give clues of the magnetic field strength, jet composition and physical processes.  The project is run by a consortium including MPIfR, Caltech, IUCAA, and Toruń Observatory.

Other projects

The research portfolio of the MPIfR VLBI department is complemented by several research projects, several of them addressing AGN jet phenomenology and the underlying processes, but also addressing Galactic objects, the Galactic Centre source SgrA*, X-ray binaries, supernovae, and supernova remnants.

RadioNet4

Our department leads RadioNet4, a project supported by the European Commission under the Horizon 2020 Framework Programme. RadioNet4 builds on the success of two preceding RadioNet projects and takes a leap forward towards the facilities of the future (such as ALMA and the SKA).

 
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