After long wait, the world is soon going to see the first image of a black hole

Credit: 'Interstellar' movie 

The world is soon going to see a real picture of a black hole. On Wednesday, April 10, astronomers from across the globe will hold "six major press conference" simultaneously, to announce the first results of the Event Horizon Telescope (EHT), which was designed precisely for the same purpose.

Of all the forces and objects in the universe that we can't see - including dark energy and dark matter - none has frustrated human curiosity so much as the invisible monster which swallows stars, dust and gases whichever come near it.

Astronomers began to speculate about these mysterious omnivorous "dark stars" in 18th century, and since then many indirect evidences have slowly accumulated. "More than 50 years ago, scientists saw that there was something very bright at the center of our galaxy", stated Paul McNamara, an astrophysicist at the European Space Agency (ESA) and an expert on black holes. 

This zoom video sequence starts with a broad view of the Milky Way. We then dive into the dusty central region to take a much closer look. There lurks a 4-million solar mass black hole, surrounded by a swarm of stars orbiting rapidly. We first see the stars in motion, thanks to 26 years of data from ESO's telescopes. We then see an even closer view of one of the stars, known as S2, passing very close to the black hole in May 2018. The final part shows a simulation of the motions of the stars. Credit: ESO/GRAVITY Collaboration

"It has a gravitational pull strong enough to make stars orbit around it very quickly - as fast as 20 years", he further added. To put that into perspective, our solar system takes about 230 million years to circle the center of Milky Way. 

Eventually, astronomers speculated that these bright spots were infact "black holes" - a term coined by an American physicist John Archibald Wheeler in mid 1960s - which are surrounded by swirling band of white-hot gas and plasma. At the inner edge of these luminous accretion disks, things go abruptly dark. 

The "Event Horizon - the point of no return - is not a physical barrier, you couldn't stand on it", McNamara explains. "If you are on the inside of it, you could never escape because you would require an infinite amount if energy. And if you are on the other side, you can - in principle!"

At its center, the mass of a black hole is compressed into a single, zero-dimensional point. The distance between this point, called "singularity", and the event horizon is the radius of black hole, or half its width. The EHT that has collected data for the first-ever image of black hole, is unlike any ever devised.

"Instead of constructing a giant telescope - which would collapse under its own weight - we combined several observatories as if they were fragments of a giant mirror", says Michael Bermer, an astronomer at the Institute for Millimetric Radio Astronomy in Grenoble.

In April 2017, eight radio telescopes scattered across the globe - in Hawaii, Arizona, Spain, Mexico, Chile and South Pole - were trained on two black holes in very different corners of the universe to collect data. Studies that could be unveiled next week are likely to zoom in on one or the other of these two.

Odds makers favour Sagittarius A* - the black hole at the center of our own Milky way - that first caught the eye of astronomers. Sag A* is 4 million times as massive as our sun and spans 44 million km across. That may sound like a big target, but for the telescope array on earth - which is 26,000 light years away - it is like trying to take a picture of a golf ball on the moon.

The other candidate is an even larger monster Black hole - 1500 times more massive than Sag A* - situated in an elliptical galaxy named M87. It is lot farther from earth as compared to Sag A*, but its size balances out the distance, making it as easy to pinpoint.

One reason that this dark horse may be revealed on Wednesday instead of Sag A* is the light smog within milky-way. "We are sitting in the plain of our galaxy. You have to look through all the stars and dust to get to the center", said McNamara. 

The data collected by the far-flung telescope array still had to be collected and collated. "The imaging algorithm we developed fill the gaps of data we are missing in order to reconstruct a picture of a black hole", the team said on their website.

Astrophysicists not involved in the project, including McNamara, are eagerly and anxiously waiting to see if the findings would challenge the Einstein's General Theory of Relativity which has never been tested on such scale.

A computer simulation shows the collision of two black holes, a tremendously powerful event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO. Credit: NASA/SXS

Breakthrough observations made in 2015 - that used gravitational wave detectors LIGO to track the merger of two black holes - earned scientists Nobel prize. As they merged, ripples in the curvature of space-time were detected, creating a unique signature. "Einstein's general theory of relativity says that this is exactly what should happen", said McNamara.

But those were tiny black holes - only 60 times more massive that our sun - compared to either of these two under the gaze of EHT. "Maybe the ones that are millions of times more massive are different - we just don't know yet."