A network of nine radio telescopes, dotted around the globe, is set to take the first ever picture of a black hole‘s event horizon in 2017.
The project, called the Event Horizon Telescope, has completed most of its technical preparations as well as extensive theoretical calculations.
It will focus on Sagittarius A**, the black hole at the Milky Way‘s centre.
Speaking at an astronomy conference in Florida, EHT team member Feryal Ozel said all the elements were in place.
She told BBC News: “We’re almost there. The phasing in of the instruments has been done, the receivers are in place and the theoretical work has been done.
“There are quite a few challenges that need to be overcome to take a picture of a black hole – it’s something that’s extremely small in the sky. But what we’re hoping for is a full array observation in early 2017.”
Prof Ozel, from the University of Arizona, gave an update on the project at the227th meeting of the American Astronomical Society.
Supermassive though it may be, the heart of the Milky Way’s black hole is not as big as you might think; the event horizon of Sagittarius A* is just 24 million km across – 17 times bigger than the Sun.
At 25,000 light years away, that makes it a pinprick. From the surface of the Earth, Prof Ozel explained, it takes up about as much of the sky as a CD sitting on the moon.
And surrounding this mysterious, spherical frontier are roiling clouds of gas and dust, which blaze with energy as they are sucked and squeezed furiously towards it.
These clouds are trouble for the EHT astronomers, who want to peer closer than ever before at this fringe of the observable universe.
One of their most important decisions was choosing which wavelength of light they would use. Radio waves were an obvious place to start, because they are scattered much less by this material than visible or infra-red light.
Then it took a lot of theoretical calculations to settle on the specific wavelength of 1.3mm, as Prof Ozel explained.
So what will this mammoth eye actually see?
“Hopefully it will look like a crescent – it won’t look like a ring,” Prof Ozel said.
This is because the glowing gas is spinning around the black hole, and a dramatic Doppler effect should make the stuff moving towards the Earth appear much brighter.
“The rest of the ring will also emit, but what you will brightly pick up is a crescent.”
In fact, the picture that emerges from the EHT next year will put general relativity on the line.
Einstein’s theory states that a mass – especially one as big as a black hole – bends space-time. And that curvature can be calculated mathematically.