May 30, 2024

The idea, the concept of a Black Hole was first imagined by Albert Einstein over 100 years ago, in 1915. His idea that a huge mass can transform and change geometry gave birth to the idea of black holes. A black hole a.k.a a Cosmic Trapdoor is a region in spacetime of such immense gravity and weight that deforms spacetime and has a gravitational force so strong that nothing, not even light, past an imaginary threshold known as the Event Horizon a.k.a The Point Of No Return can escape it.

Astronomers believe that these black holes, which could be millions or billions the times of the mass of our Sun, exist and inhabit the centres of almost all galaxies. For years black holes have been marooned in the imagination of artists and sophisticated computer models’ algorithms like the kind used in Christopher Nolan’s outer-space epic “Interstellar.” This all changed on Wednesday, 10th April 2019 when we were able to see the unseen.

The Event Horizon Telescope, putting Einstein’s theory to test in the most extreme conditions of the universe, aims to capture images of supermassive black holes using a global network of radio telescopes to create a virtual telescope about the size of Earth.

This incredible first picture depicts luminous gas swirling around a brobdingnagian black hole at the centre of a galaxy in the constellation Virgo 54 million light-years away – M87 (Messier 87). The bright light, which resembles the Eye of Sauron, a reminder yet again of the implacable power of nature, is gas falling towards the black hole at a temperature of several billion degrees which causes the event horizon to appear as a silhouette whose size and shape are predicted by Einstein’s theory.

What is the EHT and how did it capture the image of the black hole?

The EHT is an international collaboration that has formed to improve the capability of Very Long Baseline Interferometry (VLBI) at short wavelengths in pursuit of directly observing the immediate environment of a black hole with angular resolution comparable to the event horizon and thus capture images of the strong gravity effects (like matter orbiting around it at the near the speed of light) around black holes.

The EHT is observing the black hole Sagittarius A*, at the centre of the Milky Way, which is about 4.3 million times the mass of our sun, while the black hole at the heart of M87 which is about 6 billion solar masses.

The EHT hunts for a shadow, or silhouette, against a bright background — the contours of the event horizon. Additionally, black hole shadows are very dim when it comes to emitting the radio signals of interest to the EHT. So, it is best to observe this silhouette in the wavelength of 1.3mm where the gas glows the brightest and where the light can travel without any disturbance from the centre of the galaxies to the Earth.

Close to the black hole the light waves appear circular but by the time they reach Earth the light waves are linear and parallel. Therefore, a picture of a black hole at this wavelength would require a telescope as huge as the planet Earth. So Prof Sheperd Doeleman of the Harvard-Smithsonian Centre for Astrophysics led a project to set up a network of eight linked telescopes – The Event Horizon Telescope (a planet-sized array of dishes) which work together in a process known as interferometry.

Atacama Large Millimeter/Submillimeter Array (ALMA)

For the EHT to work efficiently, good weather was needed at all the 8 telescope sites. Before switching on the telescopes, the researchers had to check the humidity as too much moisture can ruin the image. To minimize the effects of weather, telescopes were built at a variety of exotic sites, including on volcanoes in Hawaii and Mexico, mountains in Arizona and the Spanish Sierra Nevada, in the Atacama Desert of Chile, and in Antarctica. Moreover, as the telescopes are spread around the world, each telescope has a different view of the black hole which makes the combined image so accurate.

For taking a picture of the black hole, all the radio dishes had to be synchronized. These dishes are curved in such a way that when microwaves hit these dishes they are reflected at a specific angle at a focal receiver. When all the telescopes (EHT) are perfectly synchronized, the recordings can be perfectly aligned to render an image. To ensure this stability and synchronization, the EHT uses atomic clocks that only lose 1 sec every 1.5 million years.

The information gathered was too much to be sent across the internet. Instead, the data was stored on hundreds of hard drives that were flown to central processing centres in Boston, US, and Bonn, Germany, to assemble the information. Here a supercomputer combined the data from all the sites compensating for the time lags of the waves getting to each telescope. The resulting data were combined into an image with extreme magnifying power.

Dr. Katie Bouman (a computer scientist who developed the algorithm that turned the telescope data into the picture of the black hole) with the hard drives

It took a team of 200 scientists and 2 decades of work to capture the image. Part of that effort was designing and building the hardware to various telescope sites. But they also had to anticipate what they might see by nailing down the physics of black holes as accurately as possible.

The EHT is by no means finished with its black hole work. Three new telescopes are being brought online -in Greenland, France and another in Arizona – and a second observing run has already been conducted in April 2018. That data is now being analyzed, too, with much more surely to come. Everything we’ve observed so far about M87 – its mass and the size of its event horizon – is consistent with Einstein’s theory. But in the future, more detailed observations could reveal unexpected features and confirm other hypotheses like if black holes spin fast enough, they form a wormhole in spacetime. Future black hole images could help confirm or refute these hypotheses.

To improve the picture quality of the black hole, we need more telescopes.

Fun Fact: Einstein hated his idea of the black hole

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