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Virtual Telescope Readied To Image Black Hole's 'Ring of Fire'
astroengine writes: With the addition of a telescope at the southern-most point of Earth, the Event Horizon Telescope (EHT) now spans the diameter of our planet and, when the vast project goes online, astronomers will get their first glimpse of the bright ring surrounding a supermassive black hole. Using a method known as Very Long Baseline Interferometry, or VLBI, astronomers can combine the observing power of many telescopes situated at distant locations around the planet. The distance between those observatories, known as the "baseline," then mimics a virtual telescope of that diameter. Now, in an attempt to make direct observations of the supermassive black hole in the center of our galaxy, located at a powerful radio emission source called Sagittarius A*, the South Pole Telescope (SPT) at the National Science Foundation's Amundsen-Scott South Pole Station has been linked to the EHT and the stage is set for a historic new era of exploring the most extreme objects in the known universe. "Now that we've done VLBI with the SPT, the Event Horizon Telescope really does span the whole Earth, from the Submillimeter Telescope on Mount Graham in Arizona, to California, Hawaii, Chile, Mexico, Spain and the South Pole," said Dan Marrone of the University of Arizona. "The baselines to SPT give us two to three times more resolution than our past arrays, which is absolutely crucial to the goals of the EHT. To verify the existence of an event horizon, the 'edge' of a black hole, and more generally to test Einstein's theory of general relativity, we need a very detailed picture of a black hole. With the full EHT, we should be able to do this."
This telescope operate in the radio bands (sub-millimeter) and not in the visible. That's why it is easy to make interferometry over very long base line. In the visible domain this is very tricky to realize over a couple of 100m (such as with the VLTI).
You can think of it as completing piece by piece the Fourier transform of the image you want to observe. Every pair of telescope gives you a measurement in the so-called UV plane (spatial frequencies). The furthest the observations point are (the telescopes) the smaller details you can get. Except this is only valid if you can measure the amplitude and phase of the electromagnetic radiation (or find a way to reconstruct it in some way). This is easy in the radio bands. But this oscillation is just too fast with visible wavelength and thus, we can not record and adjust offline, we have to interfere the waves right away...