Doddle
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RE: What TV show did you last watch?
(12-06-2020 20:48 )Dan Volatile Wrote: How to See a Black Hole: The Universe's Greatest Mystery
BBC - 2019
I would say the Universe's greatest mystery is its origin but despite the hyperbolic title this documentary gives an ok account of the Event Horizon Telescope Project which spent 10 years and 30 million pounds on the effort to produce the first image of a black hole.
Supermassive black holes are known to reside at the centres of galaxies and they produce large amounts of light and other radiation from the gas and dust which is heated to high temperatures as it swirls around the black hole in an accretion disc. The one at the centre of our milky way has the mass of four million suns which can be measured by observing the speeds of stars or gas clouds which orbit it. The EHT team were therefore trying to image the hot disc of matter which should surround the black shadow of the hole itself.
EHT consiste of eight radio telescopes from as wide an area of the Earth's surface as possible (including one at the South pole). The data is combimed using a technique called VLBI (very long baseline interferometry) to produce an image with a resolution as great as one telescope the size of the Earth would have produced. In practice this is extremely difficult as the positions of the instruments has to be know to millimetre precision and the timings have to be coordinated using atomic clocks which are accurate to one second in ten milllion years.
Needless to say the experiment was a success or there would have been no documentary, and the image that they produced was of the hole at the centre of the galaxy M87 in the constellation Virgo. One thing they should have mentioned is that there will be a ring of light surrounding the entire edge of the hole's event horizon because even if it is viewed edge on, light will be bent around the whole surface by the hole's graviational field.
This was repeated a few weeks back, where I saw it. Quite an optimistic if far-fetched project, just as well it worked. Peter Capaldi doing the narration was a nice touch.
John Simpson Wrote:The pathology of wrongdoing is far more widespread and reaches far deeper than most of us would prefer to think.
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