The first image of a black hole: What's the big deal?

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Recently, a network of radio telescopes spread across the Earth called Event Horizon  Telescope pieced together petabytes of data to unveil the first-ever image of a black hole. This is one of the most monumental feats of human ingenuity, engineering and curiosity to date. But why is it such a big deal? How can we see a black hole in the first place? And why is that orange, blurry image so groundbreaking? Let me break it down for you.

On the 10th of April, a group of researchers from a variety of fields unveiled this image. This experiment had been first proposed by Prof Heino Falcke, of Radboud University in the Netherlands. He told BBC News that the black hole was found in a galaxy called M87.

"What we see is larger than the size of our entire Solar System," he said.

"It has a mass 6.5 billion times that of the Sun. And it is one of the heaviest black holes that we think exists. It is an absolute monster, the heavyweight champion of black holes in the Universe."

Where is this black hole?

This massive black hole is around 55 million light years away from earth. That means, the light that we can see in the image left the source 55 million years ago - shortly after the dinosaurs went extinct (by shortly, I mean 10 million years - a mere blink in cosmic time).

We think most large galaxies have supermassive black holes at their centre. M87 is no exception, and neither is our own home, the Milky Way. The black hole at the centre of our galaxy is called Sagittarius A* pronounced A-star (which is kind of obvious that it’s “a star”...or at least used to be...maybe...anyway, moving on).

This experiment also took an image of our own black hole, but it’s not much brighter than the image taken of the much more distant one since Sag A* is much smaller - a mere 4 million times the mass of our sun. The one in M-87 is over a thousand times bigger.

In this X-ray ( Chandra ) and radio ( VLA ) composite image, hot matter (blue in X-ray) from the Virgo cluster falls toward the core of M87 and cools, where it is met by the relativistic jet (orange in radio), producing shock waves in the galaxy's interstellar medium. Source: Wikipedia

In this X-ray (Chandra) and radio (VLA) composite image, hot matter (blue in X-ray) from the Virgo cluster falls toward the core of M87 and cools, where it is met by the relativistic jet (orange in radio), producing shock waves in the galaxy's interstellar medium. Source: Wikipedia

What is a black hole anyway?

Well, stick your head between your legs and….okay okay, I’m not going to make any Uranus jokes on this one. Promise. Moving on. Like its name, a black hole is best described as a hole in spacetime. Einstein first hypothesised it when he was working on the General Theory of Relativity. He imagined a situation where a very massive star dies and collapses in on itself. Something like what will happen to me if I keep putting on weight like this.

If you allow me to digress for a moment, I just want to go into a brief description of what happens when a star dies. A star is kept stable when its outward pressure of nuclear fusion balances out the inward pressure of gravity. When it burns through its hydrogen and moves on to fusing heavier substances like helium, (carbon and oxygen in heavier stars) the balance begins to waver. It then expands and contracts a few times and then finally collapses and puffs out its outer layers of the atmosphere into what we can see as planetary nebulas. Stars like our sun then collapse into a white dwarf and bigger stars can go nova or supernova (the brightest event in the universe) and can collapse into more massive objects like neutron stars, which are the weirdest things, really. Let’s quickly dive into what they are:

  • White Dwarf: A medium-sized star like our sun would collapse into a white dwarf. That’s a very small object but almost as massive as a star. It’s also incredibly dense.

  • Neutron Star: A more massive star than our sun could collapse into a neutron star - where the gravity would be so strong that all its protons and electrons would get squished together to make neutrons. It’s essentially a single massive atom. To know more about these, you need to check out this video.


  • Pulsars & Magnetars: These are essentially neutron stars with weird properties they display like massive magnetic fields (magnetars) that emit very high energy radiation like x-rays and gamma rays, or rapid regular pulses of radio waves (pulsars) which emit radio waves at up to 700 times a second.

  • Quasars: These are otherwise called Quasi-Stellar Radio Sources, but Quasars roll of the tongue a bit better. Quasars give off a massive amount of radiation, which we can see as radio waves, and are thought to be about the size of our solar system. It was calculated that the only way a body could give off such an amount of radiation, would be if there was a black hole at its centre. Which brings us back to Einstein.

  • Black Holes: So Einstein wondered what would happen if a star that was so massive and collapsed into itself so violently when it died that it would form a body with so much mass and in turn so much gravity that even light couldn’t escape? If light, the fastest massless particle/wave in existence, couldn’t escape, neither could anything else. This kind of body could potentially rip a hole through spacetime, where things could fall in, but could never come out. (I think all the ball-point pens I’ve ever owned have fallen into a black hole somewhere.) All the laws of physics would break down in such a place. Einstein didn’t like the idea but couldn’t help but accept that it was a very possible occurrence.

Since his time, astrophysicists have gone on to discover all these different types of dead stars, including quasars, which most probably had a black hole at its centre. We have focused our most powerful telescopes at these objects and seen the evidence of their existence, but we never got to see one face to face.

After all, it’s a black hole. And space is black too. How the hell can we see such a thing?!

We can see its influence on its surroundings. For instance, a quasar is seen because of the high energy radio waves emanating from the disk of matter falling into the black hole. This accretion disk orbits at near light speed and heats up due to friction up to millions of degrees Celsius.

We can see that radiation.


Why haven’t we manage to take a picture of a black hole until now?

The plumes of superheated gas ejected from the poles of the black hole can be visible, as is the glow from the accretion disk, but the black hole is a tiny dark spot in the middle of all this. That’s the hard part of black hole astronomy. As for the one in the middle of our own galaxy, we noticed how massive stars were orbiting at incredible speeds around an invisible point. A really freaky sight if you ask me. One of these stars, called S2, has been seen reaching speeds of 5,000 km per second at its closest approach to the black hole.

10-year time-lapse of the stars orbiting Sagittarius A*

10-year time-lapse of the stars orbiting Sagittarius A*

The black hole at the centre of M87 was chosen because of its sheer size and level of activity, meaning how much matter it’s eating. Our own black hole Sagittarius A* was chosen because it’s so much closer to home. But the scientists working on this problem had one challenge to overcome - they calculated that the telescope they needed to be able to see these black holes up close would have to be the size of the earth. And it had to be a radio telescope because radio waves would be the only wavelength of electromagnetic waves that would reach across all the space and through all the dust and gas in between.

I’m going to let that sink in for a bit. A telescope the size of the planet we live on!

How is that even possible?

The only way to make this happen was to use 8 arrays (a collection of many individual antennae) of radio telescopes spread across the planet and then stitch all the data from them together to make it seem like it was taken by a telescope the size of the planet. This method is called Very Long Baseline Interferometry.

So that’s what a group of over 200 scientists from 59 institutes across 29 countries did. After a lot of persuasion by Prof Heino Falcke, the European Research Council agreed to fund the project to the tune of 40 million GBP. This network of telescopes came to be called the Event Horizon Telescope (EHT). They focused on the target black holes for certain periods of time and collected massive amounts of data in the process.

Back in MIT, USA, a post-doctoral scholar by the name of Dr Katie Bouman created an algorithm that would sort through the petabytes of data that was collected and flowing in from all the radio telescopes (the ones from Antarctica took 6 months because they had to wait for summer to arrive). The picture of her face when the algorithm finally spat out the image has already gone viral.

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So what?

The images of the black holes are blurry because of their size and distance. But their importance is monumental. We have come so far from Einstein’s first theories describing this hypothetical object. Through the years, it became the muse of scientists like Stephen Hawking and storytellers like Christopher Nolan and so many more. Black holes are an idea that is so bizarre that it fires up the imaginations of everyone that comes across it.

Over the years, astrophysicists have added to the study of black holes, building on Einstein’s work with current observations, calculations and theories. They have produced models and predictions of how a black hole will look and behave. A lot of those were actually used by Kip Thorne, an astrophysicist and scientific consultant for the movie Interstellar, to help the special effects team of the movie create a realistic representation of Gargantua, the black hole around which the whole movie revolved, and the reason for its mindbending ending. That visual representation is said to be the most accurate simulation of a black hole ever and has been used for further research into the topic.

The reason why this image doesn’t look like the one from the movie is that we’re looking at it from above – closer to one of the poles. And of course, this is the real thing and that was a simulation for a movie.

Of course, there have been other models created by astrophysicists since then that look at all the variations a black hole can manifest for observations like the ones made by the EHT.

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This infographic details the locations of the participating telescopes of the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA). Their goal is to image, for the very first time, the shadow of the event horizon of the supermassive black hole at the centre of the Milky Way, as well as to study the properties of the accretion and outflow around the Galactic Centre.

What am I seeing here?

Credit: EHT

Credit: EHT

The glowing ring is the super-hot accretion disk that’s spinning into the black hole. Some of the matter is travelling at almost half the speed of light and has transformed into plasma – the state of matter beyond solid, liquid and gas. The central dark area is actually the whole black hole's event horizon, both back and front. Light is being bent quite violently around here. Can you imagine if someone took a picture of you if you bent like that? You would be in the centre, and around you would be a weird, warped halo of your whole back, like the freakiest circus mirror ever made. Here’s a better explanation:

https://www.youtube.com/watch?v=zUyH3XhpLTo&t=2s

The most amazing thing is, all those predictions and models that were made were confirmed in the images. Once again, Einstein’s predictions have been validated!

And you know what? Even if the image of the black hole was different, and Einstein and all his successors were proven wrong, and this whole branch of astrophysics had to be scrapped, it would still be a celebration. Because if all this was wrong, it must mean there is a different answer, and that we have so many more questions to ask now, and so much more work to do. That’s science, people. Science revels in questions, it loves being proven wrong as much as it gets proven right.

Conclusion

This is the power of science. This is the pinnacle of human curiosity.

This is what happens when people across the world work together towards a seemingly impossible goal.

This is what happens when we stand on the shoulders of giants and still try to prove them wrong. And when we use evidence and observations together to find the amazing wonders of reality. Fortune tellers have absolutely nothing on the amazing predictions that science can make.

This is why it’s important to always question the status quo, to always strive for evidence-based answers,  and to always be curious about the universe around us and within us.

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