If we one day want to explore the galaxy (let alone the rest of the universe) humanity has a speed issue. In late 2023, NASA’s Parker Solar Probe achieved the highest speed ever achieved by a human-made object, clocking in at 635,266 kilometers (394,736 miles) per hour.
While impressive, that’s only 0.059 percent of the speed of light. Visiting our closest neighbor Proxima Centauri, 4.2 light-years away, at these speeds would take around 7,700 years, making generational ships (or robotic probes) necessary to explore it or any other interesting star further away.
Such large ships would require a lot of propellant to get us anywhere near the velocities we would need to reach the stars. Physicists have proposed various methods to do this using current physics, and more speculative ways such as warp drives, with the goal of accelerating a useful-sized spaceship to these speeds without expending a huge amount of fuel.
One such idea is to create an artificial black hole, and then power the spaceship using the Hawking radiation emitted from the event horizon.
“A stellar-mass black hole forms when a star with more than 20 solar masses exhausts the nuclear fuel in its core and collapses under its own weight,” NASA explains. “The collapse triggers a supernova explosion that blows off the star’s outer layers. But if the crushed core contains more than about three times the Sun’s mass, no known force can stop its collapse to a black hole.”
A black hole of that size – or a supermassive black hole – would be too large to usefully power a spaceship, which would have to drag the black hole along with it, requiring it to be of similar mass. Besides this, smaller black holes emit higher temperature and energy radiation, making them more useful for powering spacecraft.
So how do we get a smaller black hole? Many physicists believe that primordial black holes could have formed in the first few seconds of the universe, when all the stuff that would go on to create the stars and galaxies was more tightly packed together.
“In that moment, pockets of hot material may have been dense enough to form black holes, potentially with masses ranging from 100,000 times less than a paperclip to 100,000 times more than the Sun’s,” NASA explains. “Then as the universe quickly expanded and cooled, the conditions for forming black holes this way ended.”
We have never detected such a black hole, and it’s still unclear if they exist at all, or at least in the numbers and size at which we might be able to detect them. So if we want a black hole to power a spaceship, we might need to create an artificial one.
In one paper from back in 2009 looking into the feasibility of black hole-powered starships, physicists noted that it would have to be powerful enough to accelerate itself to speeds approaching that of light in a reasonable timeframe, be small enough that we can get enough energy to make it, and large enough that we can focus the energy needed to make it. Doing the math, they found that such a black hole could plausibly be made, and fairly quickly at that.
“We find that a black hole with a radius of a few attometers at least roughly meets the list of criteria,” the team writes in their paper. “Such BHs would have mass of the order of 1,000,000 tonnes, and lifetimes ranging from decades to centuries. A high-efficiency square solar panel a few hundred km on each side, in a circular orbit about the sun at a distance of 1,000,000 km, would absorb enough energy in a year to produce one such BH.”
The idea – known as a kugelblitz – is that focusing enough energy into one tiny point would create a black hole (with mass and energy being equivalent).
The team believes such a black hole could accelerate itself to relativistic speeds in a matter of decades.
While collecting the energy needed (never mind focusing it to a precise point needed to create a black hole) would be a hell of a mission, creating a drive from it is even more logistically challenging. The team proposes that the black hole could be used as a power plant – surrounding it with collectors that accumulate the dense energy emitted from the horizon. Alternatively, the spaceship could generate thrust by directing gamma rays.
“We could add a thick layer of matter which would absorb the gamma rays, reradiate in optical frequencies, and focus the resulting light rays,” the team writes. “An absorber which stops only gamma rays heading towards the front of the ship and allows the rest to escape out the back causes gamma rays to radiate from the ship asymmetrically. In this way, even the escaping non-absorbed gamma rays contribute some thrust.”
While a cool idea (and perhaps possible), recent papers have suggested they might be impossible thanks to quantum effects.
While it could be possible using primordial black holes, that would involve finding them first. Should they exist, that may be possible using the upcoming Nancy Grace Roman telescope. But don’t hold your breath for finding one of the right size, and near enough to be useful for powering awesome black hole starships.
The paper is posted to the pre-print server arXiv.
Source Link: How Humanity Could Power Starships By Creating Artificial Black Holes