An interstellar mission to study a black hole up close: science fiction or reality?

Black holes are one of the great enigmas of the universe. Even the most brilliant minds of modern physics have been unable to unravel what exactly happens inside them, where a point of infinite density known as the singularity lurks. Nor is it known what happens when they cross their boundary, the so-called event horizon . There are several theories, but almost no certainties. Known for a gravitational pull so intense that not even light can escape, these ghosts of what were once giant stars represent much more than mysterious cosmic objects: they are natural laboratories for testing the limits of physics.

In this context, renowned theoretical physicist Cosimo Bambi , a researcher at Fudan University (Shanghai, China), proposes an idea that is, to say the least, bold: sending tiny interstellar spacecraft to the black hole closest to Earth, with the mission of collecting firsthand data and verifying whether what Albert Einstein predicted in his theory of general relativity more than 100 years ago remains valid under extreme conditions. His proposal was published this Thursday in the journal iScience , part of the Cell Press group.

“It's true,” Bambi begins via video call from China, “it sounds like science fiction, but I don't think it is. It's something realistic, not for now, but for the next few years.” The plan outlined by the physicist is based on an already risky assumption: the existence of a black hole 20 or 25 light-years from Earth. The first challenge would be finding it. Detecting one of these cosmic monsters in isolation is difficult because they don't emit light or other forms of radiation, so their existence can only be inferred based on interactions with other objects, as if they were invisible giants. The closest known is 1,560 light-years from our planet. But Bambi insists that probability and the use of radio telescopes or the detection of gravitational waves could help locate one closer. Thus, according to the author's calculations, a nanoprobe would take between 60 and 75 years to reach the black hole, and data transmission would add another 25 years. In total, the project would last 80 to 100 years.

Once that initial challenge is overcome, the technological race would begin. Bambi's proposal includes the use of nanocraft, tiny special probes weighing just a few grams, equipped with all the necessary instruments to take measurements, and sails that would be propelled by powerful laser beams from Earth at one-third the speed of light.

Then comes the third challenge: what to do once the mission reaches its objective. The physicist proposes several verification processes, including the functioning of space-time around the black hole, testing the existence of the event horizon , and investigating whether the fundamental constants of physics change in the presence of such intense gravitational fields. To do this, Bambi thinks the ideal approach would be to send two nanocraft. One—let's call it A—would remain at a certain distance and monitor the other—B—which would orbit near the black hole, emitting periodic signals. The alterations in these signals would reveal whether or not the metric follows theoretical predictions. A second experiment would study the existence of the event horizon . Craft B would drop toward the black hole , and A would measure how long its signal remains active before disappearing.

All of this, if the spacecraft manage to enter orbit and survive such a hostile environment. "I'm not saying it's possible to do this now, but it deserves to be discussed within the community," the scientist explains. He adds that the spirit of his idea is to "stimulate" his colleagues and test whether the pillars on which modern physics has stood for more than a century are still solid enough.

The oldest black hole

“In the end, it's not just about answering scientific questions , but also philosophical ones like what exactly time is or the origin of the universe,” Bambi points out. These are mysteries that current equipment can't resolve even if they try. However, some tools like the James Webb Space Telescope keep providing surprises. The latest, published this week in The Astrophysical Journal Letters , detected the oldest active black hole to date. Analysis of the light emitted by the CAPERS-LRD-z9 galaxy—located more than 13.3 billion light-years from Earth—has allowed scientists to find the fingerprint of a black hole 300 million times more massive than the Sun, lodged in its center and already there wreaking havoc when the universe was barely 500 million years old.

Some of the postulates raised throughout the Bambi article are based on known technologies. For example, the use of nanocraft propelled by light beams. Back in 2016, Stephen Hawking and other astronomers presented Breakthrough Starshot , a project to reach Alpha Centauri, the closest star system to the Sun, using these devices. But beyond that, the experts consulted have been rather skeptical of Bambi's plans.

“This project doesn't seem realistic to me,” notes Pablo Pérez González, a researcher at the CSIC's Center for Astrobiology. The scientist agrees that the interest in studying an astronomical object up close is “extraordinary” due to the amount of information that can be obtained. “It's like comparing seeing a cat on a cell phone with touching, smelling, or hearing it,” he asserts. But he believes feasibility must be considered and a realistic plan established before rushing into writing theories. “Thinking about something like this is commendable and interesting; it's like going from reading about visiting the Moon in a Jules Verne book to actually doing it. But is that science?”

Carlos Barceló, a researcher in the theoretical physics group at the Institute of Astrophysics of Andalusia, points in the same direction. “I think the idea is a guided speculation. The researcher is well-known in the field of gravitation, so he really knows what he's talking about, but his article is highly speculative,” he comments. For Barceló, each of the points developed in the Bambi plan involves extremely high levels of technological development, so it's difficult to know if it will be viable for the next 100 years. “The margins of error are enormous. This is more appropriate for an essay than a scientific article,” he reflects.

Bambi isn't discouraged. "In science, experiments or ideas often aren't for a single generation and often take years," he explains. For him, "the real challenge in all of this is luck." Astrophysicists don't know where the nearest black hole is . "If it were 20 light-years away, the mission would be possible; if it were 40 or 50, it would become much more costly and complicated, and the project would have to be abandoned," he asserts.

Discovering such a nearby black hole would already be a major breakthrough and would attract the scientific community's interest in studying it. "The real challenge is convincing colleagues that this is worthwhile. If there's motivation, the technology can be developed," Bambi explains. In this regard, Pérez González emphasizes that interstellar missions to visit nearby stars "are much more viable" and that "part of the objectives presented by the author could be addressed."

Barceló agrees: “Stimulating the creation of microsatellites that can be sent to distant locations , in a more reasonable timeframe, is very interesting and will be developed sooner or later.” In fact, some research is already underway to send microships powered by these technologies to planets near the edge of the solar system. “That seems to me to be the closest thing to being feasible,” he adds.