Radio Astronomy/VLB Interferometry

Radio interferometry is used for the very detailed investigation of extragalactic objects including their centres. The method used is Very Long Base Line Interferometry (VLBI), which utilises the possibility of combining telescopes from eleven European countries to form one giant telescope within the European VLBI networks (EVN). Telescopes in the US are also used for global VLBI experiments.

The investigations focus on the centres of active galactic nuclei and their jets. One emphasis here is the imaging of the direct vicinity of the “central engines” in active galactic nuclei. This is where the super-massive black holes are assumed to exist.


Jets are generated when an astronomical object (young star, black hole) collects (accretes) gas from a rotating disk. Only a portion of the gas from the disk reaches the object; the other portion streams away from the object at right angles to the rotational plane. The jets are usually collimated by magnetic fields.

Research Topics

  • Structure of selected active galactic nuclei with three-millimetre VLBI observations on the sub-milliarcsecond scale
  • Chart of VLBI structure investigations of a random sample of around 300 active galactic nuclei at three millimetre wavelength
  • Long-term monitoring programme of structural changes on the parsec scale in the jets of active galaxies with VLBI at 15 gigahertz
  • Multi-frequency VLBI monitoring programme of 3C273 and 3C279 at full polarization on a two-monthly basis
  • Monitoring observations of the emission of active galactic nuclei (AGN) from radio to gamma wavelengths for the study of physical processes in jets
  • Systematic flux density measurements of short-term variable (IDV = Intra-day variable) active galactic nuclei to study the physical causes of the variability
  • VLBI investigation of the synchrotron opacity in jet centres and the consequences for wide-angle astrometry
  • VLBI survey to find sources for the linking of reference systems at visible and radio wavelengths
  • VLBI investigations of the expansion of selected supernovae
  • Mass distribution of massive galaxies with the aid of VLBI observations of the images of quasars via gravitational lenses
  • Collisions of galaxies and the role of massive black holes
  • Participation in the international Event Horizon Telescope for VLBI measurements of black holes on the microarcsecond scale at one millimetre wavelength with the involvement of the APEX telescope


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