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Photographing the invisible: Black holes

People everywhere take photos of everything all the time. But last week, a photo was taken that’s never been taken before.

Some called it impossible. But with the help of over 200 scientists and eight telescopes positioned around the globe, they did it.

“I always kind of believed in them, but seeing them for real for the first time helped solidify it,” said Ed Graham, a fourth-year student at the University of Florida.

The Event Horizon Telescope (EHT) team, piloted by project director Shep Doeleman, produced an image of Messier 87 (M87), a supermassive black hole more than 50 million light-years away. Doeleman, the senior research fellow from the Harvard-Smithsonian Center for Astrophysics who’s now on the 2019 TIME 100 list, was almost a professor at the University of Florida.

“He came down and interviewed, and it went very well,” said Stephen Eikenberry, an astrophysics professor at UF. “We were very excited and said we’d be happy to accept him in the department.”

But Doeleman’s wife ended up taking a faculty position in the Boston area, and he stayed with her. There, he worked with the EHT team to overcome the many obstacles standing in the way of visual evidence of black holes. 

The concept of black holes stems from Albert Einstein’s theory of general relativity. Over the years, observations and calculations have supported their existence.

“At the time, Einstein himself didn’t even know if black holes were real,” said Naibi Mariñas, a UF astronomy professor.

Nowadays, though nearly all astronomers believe in black holes, some have proposed what Eikenberry deemed “increasingly fringe” alternative theories. Doeleman and the EHT team searched for more tangible evidence to support the existence of black holes.

“The definition of a black hole, to me at least, is something that has gravity so strong not even light escape from it,” Eikenberry said.

But how can they take a picture of something that emits no light? Well, on the edge of the black hole is what’s called the event horizon — the point of no return. According to Einstein’s predictions, a black hole would be essentially invisible aside from a ring of light along the event horizon. What they’re actually capturing is a silhouette of the black hole.

There are a few reasons why this task seemed impossible. First, to make out an image of something 50 million light-years away — even if it’s 6.5 billion times the mass of the Sun — the picture must be incredibly sharp. To give a size reference, one EHT member equated the mission to photographing an orange on the moon.

To improve the resolution, they had to increase the size of the telescope. The EHT used a technique called interferometry, which combines inputs from multiple telescopes. They positioned eight telescopes in different countries around the world.

“We have a telescope that’s effectively the size of the planet Earth” Eikenberry said.

The telescope detects radio waves instead of visible light, because their shorter wavelengths allow for even better resolution. But shorter wavelengths are more easily perturbed by things like water vapor in the atmosphere.

“Everything from Chile to Spain to California to Hawaii — they all have to have good, dry weather all at once, and that’s tricky,” Eikenberry said.

Even after collecting the data the right way and at the right time, the team ran into another problem. What they had was not gigabytes or terabytes but petabytes of data. It was so much information that, even after improving computing power and receiver technology, it would have taken months to send the data wirelessly. 

So they loaded it all onto physical hard drives and flew them around the world on airplanes. It took nearly two years to the date after collecting the data to construct the image the EHT put out on April 10. 

“This is really rock-solid evidence,” Eikenberry said. “To me, it’s proof that we’ve been right for a while. Black holes really do exist, and they have all the properties we thought.”

This discovery was one step away from being a UF triumph.

“Oh man,” Mariñas said. “That would have been amazing publicity for the university and the department if he were here.”

While Doeleman did not end up at UF, his team’s accomplishment has affected the field and the world. Einstein won once again — this time in an unprecedented fashion.

“This is a reminder that the universe is a wild and awesome and extreme place, and there are things up there that are beyond even our wildest dreams,” Eikenberry said.


Published by Zack Savitsky

Freelance science writer and founder of Science Communigators

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