Here’s what you’ll learn when you read this story:
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It may be possible for a swarm of ultralight nanocrafts—propelled by a laser and traveling at a third of the speed of light—to make it to a black hole within about a century.
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For a spacecraft like that to reach a black hole in such a relatively short time, there would have to be a black hole 20-25 light-years from Earth, and none so close have been observed yet.
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Observing a black hole so close could answer questions that might warp the rules of physics.
On April 10, 2019, a black hole broke the internet. The first-ever image of a black hole—starring the supermassive black hole at the center of the galaxy Messier 87—was published by the Event Horizon Telescope (EHT). In an equally impressive follow-up, our own galaxy’s supermassive black hole (Sagittarius A*, sometimes shortened to Sag A*) would be imaged by EHT three years later.
So, we can finally see these things. What we can’t yet do is send a spacecraft to one.
But astrophysicist Cosimo Bambi (from Fudan University in China) has a vision. He sees a visit to a black hole happening within the next century—if we can develop a spacecraft light enough to be shot through space by a laser beam, that is. While Sag A* is a staggering 26,000 light-years from Earth, and Gaia-BH1 (the closest known stellar-mass black hole) is 1,560 light-years away, they may not be our only visitation options. Bambi thinks there could possibly be a smaller black hole hiding as close as 20 to 25 light-years away.
He may be (approximately) right. While 20 light-years may be something of a stretch, in 2023, a team of researchers from the University of Padua in Italy and the University of Barcelona in Spain found that there could be stellar-mass black holes as close to Earth as 150 light-years away. These alleged black holes are thought to exist in the Hyades open cluster—a horde of stars, close in age and chemical composition, held loosely together by their gravitational pull. When the team ran simulations that were supposed to end up matching the mass and size of the cluster, the only way they could reach those numbers was by including black holes.
Whether these black holes actually exist, however, remains to be proven. They will be exceedingly difficult for telescopes to observe because, as their name implies, black holes emit no light. And stellar-mass black holes lack the massive accretion disks that made it possible to image the M87 black hole and Sag A*. On top of that, even if—as Bambi suggests in a study soon to be published in the journal iScience—the closest black holes are slightly further from us than 20-25 light years away, and hypothetically could be reached by a spacecraft traveling at the speed of light over a century and a half, there is still the issue of creating a spacecraft light and fast enough to trek over there.
The proposal? Micro-spacecraft with light sails. These have been proposed as a way to observe distant objects up close before—the Breakthrough Starshot initiative is looking to send a swarm of nanocrafts to the nearest star system, Alpha Centauri. And those nanocrafts are similar to what Bambi is considering. No heavier than a paperclip, these tiny space probes with microchips on board will be attached to light sails propelled by a ground-based laser. Breakthrough Starshot is aiming for speeds of up to 100 million miles an hour (a third of the speed of light), and Bambi is pushing for about the same.
Spacecraft traveling at a third of the speed of light would only take 70 years to reach a black hole 20 to 25 light-years away (and data beamed back from the mission will take another two decades to reach us). If there are none that close, their next port of call would be the Hyades cluster—a journey that would take at least 420 years.
Now, none of this can be done before the technology is actually developed. But Bambi thinks that the lower costs and technological advancements needed for a nanocraft swarm may actually evolve within 30 years.
“It may sound really crazy, and in a sense closer to science fiction,” he said in a recent press release. “But people said we’d never detect gravitational waves because they’re too weak. We did—100 years later. People thought we’d never observe the shadows of black holes. “Now, 50 years later, we have images of two.”
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