Humanity got its first glimpse last Wednesday of the cosmic place of no return: a black hole. And it’s as hot, as violent and as beautiful as science fiction imagined.
In a breakthrough that thrilled the world of astrophysics and stirred talk of a Nobel Prize, scientists released the first image ever made of a black hole, revealing a fiery doughnut-shaped object in a galaxy 53 million light-years from Earth.
“Science fiction has become science fact,” University of Waterloo theoretical physicist Avery Broderick, one of the leaders of the research team of about 200 scientists from 20 countries, declared as the colourised orange-and-black picture was unveiled.
The image, assembled from data gathered by eight radio telescopes around the world, shows light and gas swirling around the lip of a supermassive black hole, a monster of the universe whose existence was theorised by Einstein more than a century ago but confirmed only indirectly over the decades.
Supermassive black holes are situated at the centre of most galaxies, including ours, and are so dense that nothing, not even light, can escape their gravitational pull. Light gets bent and twisted around by gravity in a bizarre funhouse effect as it gets sucked into the abyss along with superheated gas and dust.
“We have seen what we thought was unseeable. We have seen and taken a picture of a black hole,” announced Sheperd Doeleman of Harvard, leader of the project. Jessica Dempsey, another co-discoverer and deputy director of the East Asian Observatory in Hawaii, said the fiery circle reminded her of the flaming Eye of Sauron from the ‘Lord of the Rings’ trilogy.
Scientists have known for decades that black holes exist, but only indirectly. Three years ago, scientists using an extraordinarily sensitive observing system heard the sound of two much smaller black holes merging to create a gravitational wave. The new image, published in the Astrophysical Journal Letters, adds light to that sound. The image showed the edges of the black hole — called the ‘event horizon’ — for the first time.
Huge Black Hole
The black hole is about six billion times the mass of sun and is in a galaxy called M87. Its ‘event horizon’ — the precipice, or point of no return where light and matter get sucked inexorably into the hole — is as big as our entire solar system.
Black holes are the “most extreme environment in the known universe,” Broderick said, a violent, churning place of “gravity run amok.” Myth says a black hole would rip a person apart, but scientists said that because of the particular forces exerted by an object as big as the one in M87, someone could fall into it and not be torn to pieces. But the person would never be heard from or seen again.
Black holes are “like the walls of a prison. Once you cross it, you will never be able to get out and you will never be able to communicate,” said astronomer Avi Loeb, who is director of the Black Hole Initiative at Harvard.
“M87’s huge black hole mass makes it really a monster even by supermassive black hole standards,” said Sera Markoff, a discovery team member at the University of Amsterdam. Some black holes are inactive, but not this one, she said. And that means it converts nearby gas and matter into energy with 100 times more efficiency than the nuclear fusion that powers the stars. Black holes like these “temporarily become the most powerful engines in the universe,” Markoff said.
Working Together Works
The project succeeded because of international cooperation among 20 countries and about 200 scientists at a cost of $50-60 million, according to the National Science Foundation.
To get an image of a faraway black hole, scientists had to get eight radio telescopes on several continents, including Antarctica, to look at the same place at the same time. In getting the instruments connected, they essentially
created one Earth-size connected telescope.
The amount of data generated was so massive that it could not be transmitted over the internet, so it was flown to data centres by jet. The data collected was equivalent to a lifetime collection of selfies from 40,000 people, said discovery team member Daniel Marrone of the University of Arizona.
And just to start to take pictures the weather had to be good at all eight telescopes on the same days in April 2017. The scientists had only 10 days to look and got four perfect weather days, three of them at the start. It then took more than a year for that data to be processed into the first glimpse of images that scientists saw in the summer of 2018.
Those images were so good that scientists at first worried that it was just too good to be true, Boston University’s astronomer Alan Marscher, who was on one of four imaging teams, pointed out.
Einstein was right
Black holes are long-time superstars of science fiction. But their Hollywood fame is a little strange given that no-one had ever actually seen one – at least, until now. If you needed to see to believe, then thank the Event Horizon Telescope (EHT), which has just produced the first ever-direct image of a black hole.
As stunning and ground-breaking as it is, the EHT project is not just about taking on a challenge. It’s an unprecedented test of whether Einstein’s ideas about the very nature of space and time hold up in extreme circumstances, and look closer than ever before at the role of black holes in the universe. To cut a long story short: Einstein was right.
Capturing the Uncapturable
A black hole is a region of space whose mass is so large and dense that not even light can escape its gravitational attraction. Against the black backdrop of the inky beyond, capturing one is a near impossible task. But thanks to Stephen Hawking’s groundbreaking work, we know that the colossal masses are not just black abysses. Not only are they able to emit huge jets of plasma, but their immense gravity pulls in streams of matter into its core.
When matter approaches a black hole’s event horizon – the point at which not even light can escape – it forms an orbiting disk. Matter in this disk will convert some of its energy to friction as it rubs against other particles of matter. This warms up the disk, just as we warm our hands on a cold day by rubbing them together. The closer the matter, the greater the friction. Matter closer to the event horizon glows brilliantly bright with the heat of hundreds of Suns. It is this light that the EHT detected, along with the “silhouette” of the black hole.
Producing the image and analysing such data is an amazingly hard task. As an astronomer who studies black holes in faraway galaxies, I cannot usually even image a single star in those galaxies clearly, let alone see the black hole at their centres. The EHT team decided to target two of the closest supermassive black holes to us – both in the large elliptical shaped galaxy, M87, and in Sagittarius A*, at the centre of our Milky Way.
To give a sense of how hard this task is, while the Milky Way’s black hole has a mass of 4.1 million Suns and a diameter of 60 million kilometres, it is 250,614,750,218,665,392 kilometres away from the Earth – that’s the equivalent of travelling from London to New York 45 trillion times.
How it was done
To photograph something so impossibly far away, the team needed a telescope as big as the Earth itself. In the absence of such a gargantuan machine, the EHT team connected together telescopes from around the planet, and combined their data. To capture an accurate image at such a distance, the telescopes needed to be stable, and their readings completely synchronised.
To accomplish this challenging feat, the team used atomic clocks so accurate that they lose just one second per hundred million years. The 5,000 terabytes of data collected was so large that it had to be stored on hundreds of hard drives and physically delivered to a supercomputer, which corrected the time differences in the data and produced the image above.
General Relativity Vindicated
The most important initial take-home is that Einstein was right. Again. His general theory of relativity has passed two serious tests from the universe’s most extreme conditions in the last few years. Here, Einstein’s theory predicted the observations from M87 with unerring accuracy, and is seemingly the correct description of the nature of space, time, and gravity.
The measurements of the speeds of matter around the centre of the black hole are consistent with being near the speed of light. From the image, the EHT scientists determined that the M87 black hole is 6.5 billion times the mass of the Sun and 40 billion km across – that’s larger than Neptune’s 200-year orbit of the sun.
(The author is Senior Lecturer in Physics, University of Hull. theconversation.com)