Tuesday 23 April 2019

Susan Kelly: ''It's poetic when nature behaves in the way you expect''

A Golden Age of Astronomy: Physicist Susan Kelly on the awe, excitement and fear sparked by this ground-breaking photograph

Collaboration of the first ever image of a black hole
Collaboration of the first ever image of a black hole

Susan Kelly

Einstein wasn't bonkers. Not that we ever doubted his brilliance. Over 100 years ago, Einstein predicted the existence of black holes in his General Theory of Relativity, and finally we know for sure he was right. Days ago, the first-ever image of a black hole was published - a fuzzy flaming doughnut from the Event Horizon Telescope (EHT) - and the science community is on fire.

When I have coffee with an astronomer, which happens frequently, as let's face it, science runs on coffee, I am never hard to convince that black holes are real. For decades, astronomers have been furiously using X-ray telescopes and optical techniques to chase black holes. The evidence was overwhelming, but crucially, always indirect. Nobody really knew for sure. There was always a nay-sayer, a scientist claiming the results were actually caused by magnetic monopoles or maybe star clusters interacting with supernovae. No pic, no proof, right?

There's no denying it now. The blurry image of a black hole in the M87 galaxy is the nail in the coffin for any doubt that black holes exist.

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Prof Peter Gallagher at the School of Cosmic Physics in the Dublin Institute for Advanced Studies believes "the image from the Event Horizon Telescope gives undeniable evidence for the existence of black holes." Prof Gallagher found the image "spectacular" when it was unveiled last Wednesday.

"I was amazed by how closely it resembled the predictions based on Einstein's theories. The dark shadow at the centre of the image shows the region of space where gravity is so strong that nothing, not even light, can escape. The bright blob along the bottom of the image comes from light that is bent around the black hole. All exactly as Einstein's theories predict," he said.

Einstein's theory explains that gravity and time are closely related. Around a black hole, gravity is so incredibly high that time slows down and almost stops. Einstein imagined time like the rubber surface of a trampoline, and a black hole like a point in the centre of this surface, pushing down to eternity.

APPLIANCE OF SCIENCE: Karen O’Flaherty and Susan Kelly at the European Space Research and Technology Centre in the Netherlands
APPLIANCE OF SCIENCE: Karen O’Flaherty and Susan Kelly at the European Space Research and Technology Centre in the Netherlands

"They've caught something that's intangible. It's almost poetic, when nature behaves in the way you expect," said Karen O'Flaherty, an Irish scientist based at the European Space Agency in the Netherlands. Karen loves the name given to this black hole, Powehi, which is Hawaiian, meaning "the adorned fathomless dark creation".

Why have black holes been so elusive, so fathomless? Basically, they're not black for nothing. Black holes have such gravitational pull that they gobble matter and even light into their centres, so that nothing can escape. The size of a black hole is defined by a so-called event horizon. This is like a boundary sphere around the centre of the black hole, its singularity. Once light hits this event horizon, it is sucked forever into its centre.

Scary, huh? Maybe that's why this picture of a black hole fills me with both awe and fear. There's the instinctive human fear of being pulled into a three-dimensional dark space, never to emerge. But there's also awe, combined with excitement. It's the anticipation about what might emerge from this discovery - what Karen refers to as the "unknown unknowns of science".

"Inside a black hole, all bets are off. Mathematics breaks down and nobody knows what really happens in there," said Richard Saxton, an astronomer based at the European Space Astronomy Centre in Spain. "If your spaceship was pulled into a black hole, you'd probably still be alive, but you'd look out the other side of the event horizon and see a universe warped by gravity."

But there's no need for fear, I guess. We're not likely to take a wrong turn into a black hole like this anytime soon. After all, it is almost 54 million light years away. To travel there at the speed of light, would take you… you guessed it, a mere 54 million years.

The Event Horizon Telescope chose to point its telescopes at the M87 galaxy, a super giant elliptical galaxy in the Virgo cluster. You might wonder why the image of the black hole is so blurry - that's because it's so far away.

Black holes are formed when colossal stars collapse with gravity, so that all their matter is squeezed into a compact mass and the atoms in the star collapse on themselves. Imagine a star 10 times the size of our Sun crammed into a sphere with a diameter the length of New York City - that's how dense a black hole is.

In fact, the black hole the EHT chose to snap was a particularly huge whopper. It's an unfathomable 6.5 billion times bigger than our Sun.

"If you took 5pc of all the stars in our galaxies and squashed them into one black hole, the size of our solar system, that's the scale we're talking here," explained Richard Saxton.

The build-up and excitement to this event was years in the making. The EHT observed this black hole in April 2017, but there was some tough number crunching to do before the image could take shape. The EHT has definitely broken new boundaries.

It would be technologically impossible to have a telescope big enough to point directly at a black hole and see it, and so the EHT came up with the idea to point eight telescopes simultaneously at the black hole.

The telescopes were dotted around the globe, so when the earth spun around, the information from each telescope filled in the gaps of the image. Luckily, the weather was on their side and there was clear weather on every one of those locations.

There was so much data from each telescope that it had to be transported on airplanes. They even had to wait months for the hard-drive from Antarctica which had closed over the winter. Finally, the data could be combined on a super computer to create this epic image.

"I'm thrilled for the EHT team, as it took decades of dedicated teamwork to make this image happen. Answering big questions in science takes time, planning and funding," said Karen O'Flaherty, who added that the European Space Agency is already deciding its future space missions for 2035-2050, called Voyager 2050, this time with the help of the general public (see panel, right).

The EHT opens up a new technique for observing black holes, and with about 300 million black holes in our galaxy alone, there's a lot of them out there. Though what the image shows is not yet fully clear. The bright light in the image may be from a halo of material spinning around the black hole. The light is brighter at the bottom, since there the material moves towards us close to the speed of light and is boosted by relativistic effects. Or it could be light from material that can't be absorbed by the black hole and is spewed off into a powerful vertical jet by magnetic fields.

The next step for the EHT team will be to produce a video from data at different time intervals, to help understand what is going on. EHT also observed a smaller black hole at the centre of our own Milky Way galaxy, called Sagittarius A*, and I'll be waiting with bated breath to see this nearby black hole.

We really are in a Golden Age of astronomy.

"With recent technological advances, astronomers have discovered thousands of new planets, detected gravitational waves from colliding black holes and now glimpsed the very edge of a black hole - the stuff of science fiction only a decade ago," said Prof Gallagher. "This recent image of a black hole demonstrates that human imagination and curiosity has no bounds and will push us to ask even more profound questions about how our universe works and our place in it."

Seeing this image has answered a profound question, about the existence of black holes. To me it has made Einstein's theory of relativity feel tangible, and yes, as a Tolkien fan, I will admit it does look coincidentally like the Eye of Sauron.

It makes me think of the recently passed Nobel Laureate Leon Lederman, who boldly stated that quantum mechanics and relativity account for over one-third of our GDP. But more on that another day.

Susan Kelly is an Irish physicist, science journalist and space industry professional based in the European Space Research and Technology Centre in the Netherlands.

The European Space Agency has invited the public to help decide on future science missions by posing the question: "What do you think are the big questions our future space missions should tackle?"

You can have your say in this ESA survey for 'Voyage 2050' until the end of June, and be included in a monthly draw.

Visit http://sci.esa.int/discovering-our-universe/

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