Black hole image: Scientists reveal first ever photo from Event Horizon telescope – as it happened

Everything starts at 2pm UK time.

Here's some speculation from Dong Lai, a professor of astronomy at Cornell University and an expert on black holes. He is not involved with the project.

“My guess is EHT will produce an image of the supermassive black hole at the center of the Milky Way galaxy and also an image of one at the center of the nearby galaxy M87. More precisely, these are images of radiating hot gas orbiting very close to the black hole. The strong gravity — the ‘event horizon’ — of black holes create a dark shadow with a distinct shape where no light can be seen," he said.

“The black hole shadow was first studied and computed more than 40 years ago by Jim Bardeen in the U.S. and by Jean-Pierre Luminet in France. These days all astrophysicists believe the existence of black holes at the center of galaxies and many of their properties as predicted by general relativity. So I don’t expect  EHT will reveal any surprises.

“Nevertheless, it will be very nice and gratifying to see the black hole shadows directly. This is very challenging because the images are heavily blurred by the interstellar gas. The EHT team is to be congratulated for overcoming many technical challenges to achieve the goal of imaging black holes.”

It's worth remembering that we don't know for sure that this will be the first ever picture of a black hole – only that the project to take one has something "groundbreaking" to announce. Here's what the European Southern Observatory said when it was announced last week.

Here's the latest from Reuters, which includes everything you need to know ahead of the announcement:

An international scientific team is expected on Wednesday to unveil a landmark achievement in astrophysics - the first photo of a black hole - in a feat that will put to the test a pillar of science: Albert Einstein's theory of general relativity.

Black holes are phenomenally dense celestial entities with gravitational fields so powerful no matter or light can escape, making them extraordinarily difficult to observe despite their great mass.

News conferences are set in Washington, Brussels, Santiago, Shanghai, Taipei and Tokyo to disclose a "groundbreaking result" from the Event Horizon Telescope (EHT) project, begun in 2012 to directly observe the immediate environment of a black hole using a global network of telescopes.

A black hole's event horizon is the point of no return beyond which anything - stars, planets, gas, dust and all forms of electromagnetic radiation - gets swallowed into oblivion. The project targeted two supermassive black holes residing at the center of different galaxies.

The Washington news conference convened by the U.S. National Science Foundation is scheduled for 9 a.m. (1300 GMT) on Wednesday. Among those due to speak are astrophysicist Sheperd Doeleman, director of the Event Horizon Telescope at the Center for Astrophysics, Harvard & Smithsonian.

The research will test the theory of general relativity put forward in 1915 by Einstein, the famed theoretical physicist, to explain the laws of gravity and their relation to other natural forces.

Einstein's theory allows for a prediction of the size and shape of a black hole. If the prediction turns out to be off the mark, the theory may need rethinking.

This is separate from another key component of Einstein's broader theory of relativity: his 1905 theory of special relativity, part of the basis of modern physics. The theory of special relativity explaining the relationship between space and time.

One of the black holes - Sagittarius A* - is situated at the center of our own Milky Way galaxy, possessing 4 million times the mass of our sun and located 26,000 light years from Earth. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

The second one - M87 - inhabits the center of the neighboring Virgo A galaxy, boasting a mass 3.5 billion times that of the sun and located 54 million light-years away from Earth. Streaming away from M87 at nearly the speed of light is a humongous jet of subatomic particles.

Black holes, which come in different sizes, are formed when very massive stars collapse at the end of their life cycle. Supermassive black holes are the largest kind, growing in mass as they devour matter and radiation and perhaps merging with other black holes.

The fact that black holes do not allow light to escape makes viewing them difficult. The scientists will be looking for a ring of light - disrupted matter and radiation circling at tremendous speed at the edge of the event horizon - around a region of darkness representing the actual black hole. This is known as the black hole's shadow or silhouette.

The scientists said the shape of the shadow would be almost a perfect circle in Einstein's theory of general relativity, and if it turns out that it is not, there is something wrong with the theory.

The project's researchers obtained the first data in April 2017 using telescopes in the U.S. states of Arizona and Hawaii as well as Mexico, Chile, Spain and Antarctica. Since then, telescopes in France and Greenland have been added to the global network. The global network of telescopes has essentially created a planet-sized observational dish.

If you want to be caught up even more, here's the Press Association's round-up of what's going on today:

Astronomers are expected to reveal the first close-up images of a monster black hole during a global event later.

Eight radio telescopes around the world have been pointed at two of the cosmic behemoths, one at the heart of our galaxy, the Milky Way, and another nearly 54 million light years away.

Now, after two years of acquiring and processing the data, the international team of scientists at the Event Horizon Telescope (EHT) programme is set to present their "ground-breaking" first results.

Media have been told to gather for press conferences in Brussels, Washington, Santiago, Shanghai, Taipei, Tokyo, and Lyngby in Denmark that are due to begin at around 2pm BST.

Black holes are regions where matter has been crushed by gravity to an infinitely small space where the normal laws of physics no longer apply.

While nothing can escape the gravitational vortex of a black hole - not even light - gas and radiation rage in a swirling eddy around the brink of the abyss.

It is this point-of-no-return precipice, called the Event Horizon, that astronomers have tried to observe for the first time.

The EHT project was launched in April 2017.

Sagittarius A (SgrA), the supermassive black hole at the centre of the Milky Way, is some 26,000 light years away.

Images of SgrA are likely to show a lopsided ring of brightness due to gravity bending light closer to the black hole more strongly than light further away.

The project may help scientists struggling to marry together two apparently incompatible pillars of physics, Einstein's theory of general relativity and quantum mechanics.

The first relates to laws of nature on cosmic scales, while the second governs the weird world of subatomic particles where it is possible to be in two places at once.

Physicist and black hole expert Lia Medeiros, from the University of Arizona, US, told ScienceNews magazine: "If general relativity buckles at a black hole's boundary, it may point the way forward for theorists."

The EHT's other target, M87, is notable for shooting out a fast jet of charged subatomic particles that stretches for some 5,000 light years.

The new observations are expected to provide clues about M87's magnetic field, which may be linked to the jet mechanism.

Here's a little piece about why this is so important, and what we might be about to learn.

There's a very unusual thing about today's news: how can you take a picture of something that swallows up all light? Here's the Event Horizon Telescope's answer to that, from its FAQ page.

It is true that a black hole itself does not emit light. However, the EHT observes the nearby surroundings of a black hole. The gas that surrounds the observational targets of the EHT does in fact radiate, so by observing this region the EHT may observe structures that result from the strong gravity of the black hole.

And here's its current advice for anyone asking about when a "real image" of a black hole will finally become available:

The images will become available once the EHT collaboration is confident that the data is fully calibrated and that all procedures have been robustly tested. With the data collected in April 2017, the exciting task of processing and analyzing these data is underway within a number of focused working groups. EHT members are actively working on understanding instrumental effects and formatting the output for imaging and science analyses that will look for the black hole "silhouette". Each of these working groups is vitally important for ultimately reaching the EHT science goals. Before the results are publicly announced, they will be reviewed and further vetted by scientists who are not members of the EHT collaboration, as a part of the standard process of peer-review required for any scientific publication.

(This is about to become out of date, we hope!)

How exactly is the picture going to be made, when the black hole is so hard to see? Through a lot of very smart work by both computers and humans, in short.

Here's an explanation from the EHT:

"The Event Horizon Telescope (EHT) collects light from the black hole using a small number of telescopes distributed around the Earth. Once the EHT has measured data from the black hole, we still need to make a picture from it - a process referred to as imaging. The light we collect gives us some indication of the structure of the black hole. However, since we are only collecting light at a few telescope locations, we are still missing some information about the black hole’s image. The imaging algorithms we develop fill in the gaps of data we are missing in order to reconstruct a picture of the black hole."

To fill in those gaps, astronomers are able to infer what the kind of things they should be seeing look like, and look for that in the data. The EHT likens it to listening to a song being played on a keyboard that has broken keys – if you listened to enough of it, you'd probably be able to work out where the missing notes are, and from that you could fill them in the gaps and work out what the whole song sounds like.

One of the two targets that astronomers have been looking at has an astonishing feature: a huge jet being thrown out of the galaxy. The black hole at its core is one of the biggest we know to exist, and we might finally get a look at it. But in the meantime have a look at that jet the galaxy is throwing out.

It comes out of the galaxy's core extends over thousands of light years.

"Only one side of the jet is seen because of relativistic effects; the jet is moving outward at nearly the speed of light and is pointed close to Earth resulting in an increase in brightness from relativistic beaming," the EHT says. "The oppositely pointed counter-jet is instead moving away from Earth at near the speed of light and so its brightness is likewise diminished."