It sounds like science fiction: a spacecraft, no heavier than a paperclip, propelled by a laser beam and hurtling through space at the speed of light toward a black hole, on a mission to probe the very fabric of space and time and test the laws of physics. But to astrophysicist and black hole expert Cosimo Bambi, the idea is not so far-fetched.
Reporting in the Cell Press journal iScience, Bambi outlines the blueprint for turning this interstellar voyage to a black hole into a reality. If successful, this century-long mission could return data from nearby black holes that completely alter our understanding of general relativity and the rules of physics.
"We don't have the technology now," says author Cosimo Bambi of Fudan University in China. "But in 20 or 30 years, we might."
The mission hinges on two key challenges—finding a black hole close enough to target and developing probes capable of withstanding the journey.
Previous knowledge on how stars evolve suggests that there could be a black hole lurking just 20 to 25 light-years from Earth, but finding it won't be easy, says Bambi. Because black holes don't emit or reflect light, they are virtually invisible to telescopes. Instead, scientists detect and study them based on how they influence nearby stars or distort light.
"There have been new techniques to discover black holes," says Bambi. "I think it's reasonable to expect we could find a nearby one within the next decade."
Once the target is identified, the next hurdle is getting there. Traditional spacecrafts, powered by chemical fuel, are too clunky and slow to make the journey. Bambi points to nanocrafts—gram-scale probes consisting of a microchip and light sail—as a possible solution. Earth-based lasers would blast the sail with photons, accelerating the craft to a third of the speed of light.
At that pace, the craft could reach a black hole 20 to 25 light-years away in about 70 years. The data it gathers would take another two decades to get back to Earth, making the total mission duration around 80 to 100 years.
Once the craft is near the black hole, researchers could run experiments to answer some of the most pressing questions in physics. Does a black hole truly have an event horizon, the boundary beyond which not even light can escape its gravitational pull? Do the rules of physics change near a black hole? Does Einstein's theory of general relativity hold under the universe's most extreme conditions?
Bambi notes that the lasers alone would cost around one trillion euros today, and the technology to create a nanocraft does not yet exist. But in 30 years, he says that costs may fall and technology may catch up to these bold ideas.
"It may sound really crazy, and in a sense closer to science fiction," says Bambi. "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."
