The very high angular resolution of Earth-based cm-wave VLBI can be
increased further in two ways, either by using longer baselines
or by observing at shorter wavelengths. The first approach leads
to "space-VLBI" (VLBI with one or more orbiting antennas),
the second approach to "millimeter-VLBI" (mm-VLBI). In the more
distant future, both techniques may be combined. This would lead
to space-VLBI at millimeter wavelenghts ("mm-space-VLBI"). To date
space-VLBI observations (e.g. with the RadioAstron mission) have
been shown to be technical feasible in the cm-bands, down to
1.3cm wavelength.
Millimeter VLBI offers a much higher angular resolution than ground
or space based VLBI at centimeter wavelengths and has another very
significant advantage:
in the spectral mm-bands it is possible to study emission regions
which appear
self-absorbed (and are therefore invisible) at longer wavelengths.
This has important consequences for a better understanding of
the physical processes acting in Active Galactic Nuclei (AGN)
and in the vicinity of supermassive Black Holes.
After years of continuous development and technical improvement,
mm-VLBI is now able to provide good quality images in the 3mm band,
with an angular resolution of typically 50-70 micro-arcseconds. At
shorter wavelengths the VLBI technique is still being developed and limited to fewer
VLBI antennas. It is also not yet available to the broader community (e.g. VLBI
with the EHT at 230 GHz (1.3 mm)). Global mm-VLBI allows compact
galactic and extragalactic radio sources to be imaged DIRECTLY with an
angular resolution which is unsurpassed by any other present
astronomical imaging method.
The "Global mm-VLBI Array" has been set up by a group of radio
observatories interested in performing astronomical VLBI observations
at millimeter wavelengths and with open access for the scientific
community. The intention is that this "network" should
perform regular, coordinated global VLBI observations in the 3mm
band. As a successor to the former CMVA (Coordinated Millimeter VLBI
Array), the "Global mm-VLBI
Array" offers to the User Community a large VLBI network combining the most sensitive radio telescopes, and
hence an improved sensitivity and image fidelity in the resulting VLBI
maps.
As the success of the "Global mm-VLBI Array" depends on the scientific
results it will produce, we invite all interested scientists to make
use of it. Please see the other documents and links on this web page
for further and more detailed information.
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