EHT
Event Horizon Telescope
The Event Horizon Telescope is an array of radio observatories from around the Globe. We link the data measured by each individual telescope together digitally to connect all antennas into an “interferometer”: a single virtual telescope that has the size of the Earth. Through this technique, the EHT has the highest resolving power in astronomy and is the only instrument capable of imaging black holes. Dutch scientists play a leading role in the steering and scientific output of the EHT and we are currently working on building our own Dutch-led telescope in Namibia – the Africa Millimetre Telescope – to join the EHT.
Infrastructure and User Services
The EHT currently consists of twelve individual observatories: The Atacama Large Millimeter/submillimeter Array (ALMA), Atacama Pathfinder Experiment (APEX), James Clerk Maxwell Telescope (JCMT), Large Millimeter Telescope Alfonso Serrano (LMT), IRAM 30 m Telescope, Submillimeter Array (SMA), Submillimeter Telescope (SMT), South Pole Telescope (SPT), Kitt Peak Telescope, Northern Extended Millimetre Array (NOEMA), Greenland Telescope (GLT), and telescopes from the Korean VLBI Network (KVN). More telescopes are expected to join the EHT in the near future. Observing proposals go through the ALMA peer-review system. For accepted proposals, EHT observations are scheduled in a ~two week window in March/April, out of which a few observing runs are triggered based on good weather/observing conditions at each of our telescopes. A single observing run takes about 18 hours, during which we collect petabytes of data from all telescopes. These data are stored on hard drives and later shipped to two central correlation centers (supercomputers) at the MIT Haystack observatory and Max Planck Institute for Radio Astronomy. The data after correlation is sent to the users, which are the PIs of the ALMA proposals. If the PIs are not part of the EHT collaboration, they will have to make sure that the other EHT observatories besides ALMA participate in the observations. The correlated data has a volume of a few Terabytes, is stored indefinitely in the ALMA and EHT archive servers, and becomes public one year after the correlation has been finished and fully verified.
Examples/description of the type of research
The primary science goal of the EHT is to image black holes. For the low-luminosity active galactic nuclei (supermassive black holes in the center of galaxies that are accreting matter at a relatively low rate) M87* and the centre of our own galaxy Sagittarius A*, the EHT has resolved the millimetre-wave emission in the direct vicinity of the black holes. This emission is produced by synchrotron radiation and produces a characteristic ring-like structure with a dark spot in the center. This black hole shadow is a telltale sign for the presence of an event horizon and allows us to test General Relativity (GR). Additionally, we can study the launching regions of extragalactic radio jets produced by a large sample of supermassive black holes. Combined with the observations at horizon-scales, we can study jet physics, accretion onto compact supermassive objects, plasma physics in extreme astrophysical conditions, and GR.
How to access the infrastructure ?
Users can submit proposals through the peer-reviewed ALMA proposal system: https://almascience.nrao.edu/proposing/call-for-proposals . The data can be accessed through the ALMA science archive: https://almascience.eso.org/almadata/ec/eht/ .