Neal Dalal: Sharpening our View of the Universe

Neal Dalal wants to photograph the unseeable.

It only seems impossible, he says, because nobody has done it yet.

Dalal envisions a not-too-distant future when he, in collaboration with scientists around the world, could combine their expertise and technologies to photograph the most mysterious and elusive objects in the universe in more detail than ever before.

Black holes do not want to be seen. They gobble everything, including light, making them visible only by the swirling chaos just outside their point-of-no-return event horizons. They’re small, distant, and camera-shy.

The iconic image of a fuzzy orange “donut” released in 2019 by the Event Horizon Telescope (EHT) collaboration gave the world its first glimpse of a black hole’s “shadow,” depicting the supermassive gravity well at the centre of the M87 galaxy.

If that EHT image represents a black hole’s baby photo, heDalal envisions the next image to be a high-definition portrait sharp enough to depict the black hole’s unique personality. Whereas the EHT used a network of radio telescopes working in tandem to capture its black hole data, Dalal wants to go thousands of times sharper by using visible light and a network of telescopes focussed like a single, planet-sized eye.

“Imagine if it were possible to do what the EHT did, but using visible light instead of radio light,” explains Dalal.  “We can instead get something, like, a megapixel image of the black hole in our galaxy.”

Dalal has made a career of investigating the universe’s most tightly guarded secrets. Before joining Perimeter’s faculty in 2017, Dalal researched neutrinos as a fellow at the Center for Advanced Study at the University of Illinois, and studied large-scale cosmic structure at Princeton’s Institute for Advanced Study. Some of his recent work places constraints on ultralight “fuzzy” dark matter in dwarf galaxies; other research reveals how dark-matter haloes shape gravitational lensing signals.

He loves a good mystery — the bigger the better. And as mysteries go, few are more vexing than black holes.

It was long believed by astrophysicists that black holes, by their very definition, could not be photographed (if they existed at all). Technological advances in the past decade alone have facilitated the kind of split-second precision and big-data crunching power required to achieve the EHT result; recent advances in technology, partly fuelled by AI, are hastening furthermore breakthroughs.

Dalal believes precision technologies have finally caught up to the theoretical aspirations of astrophysicists.

“This idea was invented decades ago — it is called intensity interferometry,” says Dalal, describing how an array of telescopes can combine light streams instead of radio waves, which boosts angular resolution by orders of magnitude.

What has happened in the decades since the idea was proposed is an explosion in technologies vital to making it a reality. A revolution in quantum sensors makes it possible to detect incoming light with unprecedented precision.

“These quantum detectors can measure single photons as they reach our detector one at a time,” Dalal explains. “They're capable of measuring the arrival time incredibly precisely. If you measure the arrival times of the photons coming in at the two telescopes, you can… reconstruct what the sky looks like with incredibly high angular precision.”

Put simply: it’s a new way of seeing.

Because researchers are dealing in visible light, which has “a wavelength thousands and thousands times smaller than radio waves,” the angular resolution of their images is boosted by orders of magnitude. The smaller the wavelength, the sharper the detail. Fuzzy orange donuts become crisp images of accretion discs, photon rings and beaming jets of energy.

Alongside the advances in quantum sensing, another technology has emerged with almost uncanny timing to supercharge the research.

“We also have this other revolution happening right now, which is the AI revolution,” says Dalal, whose collaborators at Perimeter and beyond are “making use of some of these modern AI methods to help with the data analysis.”

Technologies that once developed independently — quantum sensing, photon-level timing, machine learning — are converging, which Dalal says is speeding up the journey of ideas from the blackboard to the lab. Even 10 years ago, Dalal’s envisioned high-res portrait of a black hole would be purely speculative; now it’s highly doable.

“Every component needed to make one of these things has already been demonstrated,” he says. “Really all that's needed is just collective will. If we could convince the community to really come together to support something like that, I feel that that would be really transformative for astrophysics.”