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Scientists Are About to Switch on a Telescope That Could Photograph a Black Hole's Event Horizon

Black holes are the most amazing objects in the known Universe. But regardless of the fact that they're believed to lurk at the center of most galaxies, the reality is that no one has ever been able to truly capture one. That's because black holes, as their name suggests, are extremely dark. They are so massive that they permanently consume everything that passes through their event horizon, even light, making them almost impossible to photograph. But that could be about to change when a new telescope network comes online in April this year.

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Named as the Event Horizon Telescope, the new Telescope is made up of a network of radio receivers situated across the planet, including at the South Pole, United States of America, Chile, and the French alps. 
The network will be online on between 5 and 14 April, and the outcomes will put Einstein's theory of general relativity through its paces like never before. The Event Horizon Telescope is based on a technique known as very-long-baseline interferometry (VLBI), which means the network of receivers will focus on radio waves discharged by a specific object in space at one time. For the black hole, they will be aiming at radio waves with a wavelength of 1.3 mm 230 GHz (1.33 mm), which gives them the best opportunity of penetrating through any gas clouds and dust blocking the black hole.

And because there are so many antennae like these all tuned on a single spot, the resolution of the telescope should be about 50 microarcseconds. To put that into perspective, it's the equivalent of being able to see a grapefruit on the Moon. That's important, because the very first target will be the massive black hole at the center of Milky Way Galaxy, called Sagittarius A*, which is in fact only the size of a pinprick in our night sky. We have never been able to directly observe Sagittarius A*, but scientists know it exists because of the way it effects the orbit of nearby stars. Based on the activities of these stars, scientists predict that the black hole is about 4 million times bigger than our Sun, but with an event horizon diameter of just 12.4 million miles (20 million km) or so across.
   
At a distance of about 26,000 light-years from Earth, that makes it a quite small target. But the Event Horizon Telescope will focus to detect the immediate environment around the black hole, and it should be able to get sufficient resolution to view the black hole itself.

"There's great excitement," leader of the mission Sheperd Doeleman from the Harvard-Smithsonian Centre for Astronomers told Jonathan Amos at the BBC this week.

"In April we are going to make the observations that we think have the first real chance of observing black hole's event horizon."

So what can we expect to see if the mission is successful?

The scientists expect the black hole to be like a bright ring of light around a dark blob.

The light is being discharged by gas and dust particles that are accelerated to high speeds just before they are torn apart and consumed by the black hole. The dark blob would be the shadow cast over that chaos. But if Albert Einstein was right, we should be seeing more of a crescent of light than a ring - because Doppler Effect should make the object moving towards the Earth appear much brighter.

"Hopefully, it will look like a crescent - it won't be looking like a ring," team member Feryal Özel said in a press conference last year. "The rest of the ring will also emit, but what you will be seeing is a crescent."

If the team is able to calculate the dark shadow cast by the black hole, that will be massive, because general relativity makes quite specific predictions about what size it should be, based on how much the black hole should bend space-time.

"We know precisely what Einstein’s theory of general relativity predicts for that size," said Özel. "Reach the edge of a black hole, and the general relativity experiments you can perform are both qualitatively and quantitatively different."

What if we observe something else? Doeleman told Amos that it's certainly a possibility, and it would dismantle the world of physics as we know it.

"As I have said before, it's never a good idea to bet against Albert Einstein, but if we did observe something that was way different from what we expect we would have to reassess Newton’s theory of gravity," he said.

"I don't think that it’s really going to happen, but anything could happen and that's the beauty of the Universe."

Given all the data scientists will need to process, we shouldn't be expecting the first images of a black hole until the start of 2018. And that's assuming there's good enough weather to get a perfect picture in the April watching window. But when those first pictures come in, it's going to be a quite an exciting moment for mankind.


"One thing that could excite the public almost as much as a Pluto flyby did would certainly be a picture of a black hole, up close and special," Ӧzel saidat the 227th meeting of the American Astronomical Society last year.

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