When you think of black holes, you probably don’t think of them being very friendly to life. With an event horizon beyond which not even light can escape, and surrounded by a swirling, superheated disk of dust and gas, they certainly don’t seem very habitable.
But a group of researchers has claimed that certain black holes may have conditions that would mean that any orbiting planets could be capable of supporting life. It’s a stretch, sure, and no black hole planets have actually been found yet – but it’s an interesting theory nonetheless.
As reported by New Scientist, the paper – a pre-print of which is available on Arxiv – explains how life requires a “temperature difference” to thrive. On Earth, we get this from the Sun and the cold vacuum of space. If this were reversed – a hot sky and a cold Sun, negative entropy – a similarly habitable temperature difference could also be provided.
For an old black hole, devoid of material in its surroundings, conditions might be suitable for life. The authors of the paper suggest a planet in orbit around such a black hole would receive about 900 watts of power, from the temperature difference between the black hole and the cosmic microwave background (CMB) of the universe at 2.7 Kelvin (-270°C, -455°F]). This would be enough for very primitive life to survive. Can we improve on this, though? Well, yes, but you have to go back to the beginnings of the universe.
About 15 million years after the Big Bang, it’s thought the CMB was a rather warmer 300 Kelvin (27°C, 80°F). Now, the temperature difference between a sedate black hole and space produces about 130 gigawatts of power, a millionth of what the Sun provides Earth, but enough to support complex life.
The authors liken their research to one of the planets described in the movie "Interstellar" – specifically "Miller’s Planet." This world is described as orbiting so close to a fictional black hole called Gargantua that it experiences the effects of time dilation. The authors note the position of the planet as depicted in the film renders the planet mostly uninhabitable. “But, with a suitably chosen orbit slightly farther from Gargantua, one can hope to find the sky conditions of the planet much closer to terrestrial,” they add.
Gargantua and Miller's Planet, as depicted in Interstellar. Warner Bros
We’re probably not going to find any planets orbiting a black hole any time soon. But the authors also note that in the far, far distant future, when all the stars have burned out, the last places for life to inhabit may be around black holes. We guess it’s comforting to know that our distant relatives in trillions of years won’t necessarily be left in the lurch.
"One might speculate of the distant future when hydrogen as the nuclear fuel for stars is exhausted and black holes, together with background radiation, become one of the few relevant sources of negative entropy," the authors added.