http://www.bbc.com/news/science-environment-38937141

Scientists believe they are on the verge of obtaining the first ever picture of a black hole.
They have built an Earth-sized “virtual telescope” by linking a large array of radio receivers – from the South Pole, to Hawaii, to the Americas and Europe.
There is optimism that observations to be conducted during 5-14 April could finally deliver the long-sought prize.
In the sights of the so-called “Event Horizon Telescope” will be the monster black hole at the centre of our galaxy.
Although never seen directly, this object, catalogued as Sagittarius A*, has been determined to exist from the way it influences the orbits of nearby stars.
These race around a point in space at many thousands of km per second, suggesting the hole likely has a mass of about four million times that of the Sun.
But as colossal as that sounds, the “edge” of the black hole – the horizon inside which an immense gravity field traps all light – may be no more than 20 million km or so across.
And at a distance of 26,000 light-years from Earth, this makes Sagittarius A* a tiny pinprick on the sky.
The Event Horizon Telescope (EHT) team is nonetheless bullish.
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This combines a network of widely spaced radio antennas to mimic a telescope aperture that can produce the resolution necessary to perceive a pinprick on the sky.
The EHT is aiming initially to get down to 50 microarcseconds. Team-members talk in analogies, describing the sharpness of vision as being the equivalent of seeing something the size of a grapefruit on the surface of the Moon.
They emphasise the still complex years of work ahead, but also trail the prospect of an imminent breakthrough.

The scientists certainly have an expectation of what they ought to see, if successful.
Simulations rooted in Einstein’s equations predict a bright ring of light fringing a dark feature.
The light would be the emission coming from gas and dust accelerated to high speed and torn apart just before disappearing into the hole.
The dark feature would be the shadow the hole casts on this maelstrom.
“Now, it could be that we will see something different,” Doeleman said.
“As I’ve said before, it’s never a good idea to bet against Einstein, but if we did see something that was very different from what we expect we would have to reassess the theory of gravity.
“I don’t expect that is going to happen, but anything could happen and that’s the beauty of it.”