With the New Year in its early run, it is always tradition to expect and anticipate a plethora of scientific marvels and innovations in their stages of inception or revelation. 2019 brings something exciting to the table, marking a step in the realm of astronomy and bringing us a photograph of possibly the most enigmatic phenomena to exist in the known universe. A mysterious name to amplify its nature, scientists believe that they have finally articulated a way to capture the event horizon of a black hole! For years, the Event Horizon Telescope has been working to bring us the first ever telescopic photograph of the event horizon.
One would think with all the popularity and public dramatization that we would have seen black holes. Quite funnily, we never have. Why, you ask? Because they are invisible. The pull of their gravity is so immense that, past a certain point, nothing escapes. This includes the electromagnetic radiation – such as X-rays, infrared, light and radio waves – that would allow us to detect the object directly. This threshold of no return is called an event horizon, and while we want to stay as far away from it as possible, it is vital in visualizing what a black hole could possibly look like. While we may not be able to see the black hole itself, we are enticingly close to seeing something as good as the occurrence itself.
But long before the Event Horizon Telescope, there was an astrophysicist named Jean-Pierre Luminet. All the way back in 1978, he already gave us what could be thought of as the very first image of a black hole’s event horizon. It is not an actual photo, but being skilled in the field of mathematics, Luminet performed, what was the first ever computer simulation on visualizing an image closest to that of a black hole. He was equipped with a 1960s punch card IBM 7040 computer.
“At the time it was a very exotic subject, and most astronomers did not believe in their existence,” said Luminet. “I wanted to explore the strange physics of black holes and propose specific mechanisms that could help to get indirect signatures of their very existence. Also, to pursue the pun, with my name ‘Luminet’ I liked much the idea of how a perfectly non-luminous star can give rise to observable phenomena.”
With the data returned by the computer, Luminet spent many painful hours plotting the points with his hands equipped with nothing more than ink and negative paper, something we struggle to visualize these days with printers around every corner. That fuzzy image – seen above – shows what a flat disc of material falling into a black hole might look like if we were close enough to see it.
It doesn’t look flat, because the intense gravity of the black hole is bending light around it. “Indeed the gravitational field curves the light rays near the black hole so much that the rear part of the disk is ‘revealed’,” Luminet explained in a paper published on arXiv last year.
“The curving of the light rays also generates a secondary image which allows us to see the other side of the accretion disc, on the opposing side of the black hole from the observer.” With this discovery, Luminet opened the doors of imagination to millions of aspiring innovators across generations who depicted their own interpretations of a black hole both in scientific forums, and on the silver screen.
The 2014 Christopher Nolan film Interstellar was lauded for its supposedly “scientifically accurate” depiction of a black hole, based in large part on the work conducted by Luminet decades earlier, and created in consultation with theoretical physicist Kip Thorne of Caltech. Visual appeal and simplicity being one of the vital factors in mass media, the movie opted for a much more diluted reality of a black hole and amplified its visuals, thus accentuating the intriguing story line and perhaps deviating from the essentials of the enigmatic phenomena’s existence.
“It is precisely this strong asymmetry of apparent luminosity,” Luminet wrote, “that is the main signature of a black hole, the only celestial object able to give the internal regions of an accretion disk a speed of rotation close to the speed of light and to induce a very strong Doppler effect.” He penned a 15-page paper on the film’s science, and Thorne himself wrote a book on the topic.
The EHT has been focusing on Sagittarius A*, the supermassive black hole at the centre of our own galaxy, the Milky Way. Although it is not pragmatic to expect a definitive picture of a black hole, it is a matter of pride to know that we are on our first steps in unlocking the mysteries of this phenomena. Given the black hole had an accretion disc during observations, we’re anticipating something that looks a lot like the work of Luminet.
The new device is made up of a network of radio receivers located across the planet, including at the South Pole, in the US, Chile, and the French alps. The network will be switched on between 5 and 14 April, and the results will put Einstein’s theory of general relativity to test and in action like never before. The Event Horizon Telescope works using a technique known as very-long-baseline interferometry (VLBI), which means the network of receivers will focus in on radio waves emitted by a particular object in space at one time.
For the black hole, they’ll be focusing on radio waves with a wavelength of 1.3 mm (230 GHz), which gives them the best chance of piercing through any clouds of gas and dust blocking the black hole. With the presence of so many antennas focused on a single spot, the resolution of the telescope is expected to be a staggering 50 microarcseconds. Too foreign a term? To paint a simple picture, this resolution is the equivalent of being able to see a grapefruit on the moon.
Based on the behavior of these stars, researchers predict that the black hole is likely about 4 million times more massive than our Sun, but with an event horizon diameter of just 20 million km (12.4 million miles). The researchers predict that the black hole will look like a bright ring of light around a dark blob. In addition, the collaboration will hopefully help us understand more about the polarization of radiation, the structure of the magnetic field, and the black hole’s relativistic jets. It’s already yielded up clues about the structure of space around the black hole.
Be it a bunch of pixelated images or something unexpected, it is certainly worth looking forward to! The announcement from the Event Horizon Telescope regarding this revolutionary step is expected to happen any day now. Do you expect the reveal to surprise you, or were the movies right after all?