Mining the Energy of Black Holes

Traveling forward in time by using the strange distortions of spacetime generated near the event horizon of a black hole may eventually become possible. Yet such undertakings would be risky and the results would be highly unpredictable and of questionable value. So a majority of people in an advanced future society may well feel that it makes more sense to exploit the unusual properties of black holes in more practical ways.

Indeed, black holes produce enormous amounts of raw energy. And it would certainly be advantageous for human beings to harness some of that energy, which could be converted to electricity to power homes, offices, public buildings, and even cars and ships. A number of scientists believe that such a goal will actually be attainable in the future. Admittedly, many difficult technical problems would have to be overcome before people could control and tap into these cosmic powerhouses. But after all, only a century ago space shuttles, artificial satellites, nuclear power, television, computers, and the Internet, all of which required the development of bold new technologies, did not exist.

Farming the energy of black holes would utilize the same basic principle used in existing types of energy production. Namely, when any kind of fuel is burned or destroyed, some of its mass is converted into energy, which people then exploit. When people burn oil or coal, only about 1 percent of the fuel’s mass is converted into energy. Obviously, this is not very efficient and produces a lot of soot and other waste materials that pollute the environment. Even nuclear reactions, like those produced in nuclear power plants, convert only 2 or 3 percent of their mass into energy. By contrast, when matter is annihilated at the event horizon of a black hole, up to 30 percent of its mass becomes energy. In theory, people could stoke such a black hole furnace by firing asteroids and other space debris toward the hole, destroying the debris and thereby generating energy. If people could find a way to capture that energy, say by installing large collection grids around the hole, Earth could be provided with seemingly unlimited power.

On an even grander scale, given further technological advances, people might actually be able to create black holes from scratch. As John Taylor explains, this would yield mass-to-energy conversions considerably higher than 30 percent:

We can envisage a technologically very advanced intelligent civilization which goes in for black-hole farming. To do this, they would spread hydrogen or helium throughout a region of a galaxy, or concentrate some already there, so that large stars were formed rapidly. These would then be used as energy generators during their nuclear burning phase, and allowed to collapse to black holes, also collecting supernova energy emitted during the short implosion [collapse] time. The resulting black holes would then be brought together in pairs by suitable methods to obtain a large fraction of their available energy. The resulting single black hole would then be finally exhausted of all its remaining available rotational and electrical energy. The amount of energy available in this way would be enormous.

Of course, humans may never achieve the level of technology needed for such fantastic engineering projects. Also, they may find it too difficult and time-consuming to travel hundreds or thousands of light-years in search of stellar black holes to exploit. However, that does not necessarily rule out human exploitation of black hole generated energy. A more modest and plausible approach would be to build instruments capable of detecting mini–black holes that stray through our solar system. Once found, such objects might be captured and mined in a manageable way. “A stream of frozen hydrogen pellets can . . . be aimed past the mini–black hole,” says Asimov,

so that it skims the Schwarzschild radius without entering it. Tidal [intense gravitational] effects will heat the hydrogen to the point of fusion, so that helium will come through at the other end. The mini–black hole will then prove the simplest and most foolproof nuclear reactor possible, and the energy it produces can be stored and sent down to Earth.

These are only some of the ways in which the highly unusual properties of black holes may someday be exploited by humanity, or by other races of intelligent beings. Only time will tell.

Hawking Radiation and Evaporating Black Holes

In 1974, English physicist Stephen Hawking surprised the scientific community by showing that black holes can give off radiation and thereby lose some of their mass. Some of the matter at the edge of the event horizon, he said, would consist of pairs of particles. One particle would be positively charged, the other negatively charged. In his book about Hawking, scholar Paul Strathern writes: “The black hole would attract the negative particle, while at the same time it would eject the positive particle. This would escape in the form of radiation.” This radiation, now called Hawking radiation, would be in the form of heat. Its temperature would be “mere millionths of a degree above absolute zero,” says Strathern, “but it would undeniably be there.”

In his book Explorations, astronomer Thomas Arny points out that, because of this phenomenon, black holes must eventually evaporate. “However,” he adds, “the time it takes for a solar-mass black hole to disappear by ‘shining itself away’ is very long approximately 1067 years! This is . . . vastly larger than the age of the universe but the implications are important: even black holes evolve and ‘die.’”