It can be dangerous - it can be a lot of fun! This is the opinion of one of the leading astrophysicists in the United States and with wit reflects on the possibilities that people could get if they were transported to the vicinity of a supermassive black hole. He suggested that progress in the development of space engines could allow us to organize "field research" of the nearest such hole.
Since the 1990s, we have known that planets can orbit pulsars, incredibly dense objects created by powerful explosions of stars. It would be reasonable to assume that they can revolve around black holes, which, surprisingly it may seem to many, have less impact on their environment than pulsars. Some of these planets may even have life, because many living things on Earth, as we know, have adapted to extreme conditions, including very high and low temperatures, acidic, saline and even radioactive environments.
Inhabited planets can be found near supermassive black holes, which are located at the center of most galaxies. Our own galaxy, the Milky Way, harbors a black hole with a mass equal to the mass of four million stars combined. The innermost stable circular orbit (SVUKO) of this object, known as Sgr A * (Sagittarius A *), is roughly equal to the orbit in which Mercury moves around our sun.
What would it be like to live on such a planet?
Before talking about the many dangers to life near a black hole, let's look at the benefits. If civilizations emerge or migrate to the vicinity of black holes, what interesting and useful things can they do there? The 10 best options come to mind:
- Use the black hole as a source of clean energy, dumping waste into the funnel of the accretion disk, around which the vortex of matter revolves. Up to 42% of the waste's own mass can be converted into radiation at the SVUKO black hole rotating at maximum speed.
- Connect some kind of engineering mechanism to the axis of rotation of the black hole like a giant flywheel from which energy can be collected.
- Ride on photon sails along relativistic jets at a speed close to the speed of light.
- Prolong youthfulness by visiting beauty salons located near the horizon of a black hole, where time flows more slowly as a result of gravitational redshift.
- Enjoy the view of the entire universe, bizarrely reflected in the gravitational lens images around the black hole.
- Open an amusement park on the so-called "photon sphere", where you can play with various relativistic effects, for example, see yourself from the back, looking straight ahead, as light bends around a black hole.
- Take everything from new possibilities of movement in space. So, when in billions of years the Milky Way merges with the neighboring Andromeda nebula, two black holes in their center will unite into a solid binary system, a kind of gravitational catapult that can launch stars and planets at the speed of light, as the author of this material explains in two articles written co-authored with James Guillochon. Travel agencies will be able to sell tickets for incredible trips to catapulted planets that will traverse the entire universe.
- Send criminals to the black hole as the most secure prison with the death penalty through the singularity. The life span of prisoners will depend on the mass of the black hole. The less serious a crime they committed, the more massive their black hole will be, and the longer they will be able to live outside the "prison walls", which will be considered the horizon of the black hole.
- Use gravitational waves emitted by small objects orbiting a black hole as a means of communication. Such signals cannot be blocked by any of the known forms of matter.
- Test the basic aspects of quantum gravity by sending groups of experimental physicists and experts in string theory on organized tours.
The main danger to astronauts who try to master these activities comes from tidal forces. As Albert Einstein pointed out in his famous thought experiment, whoever is inside a falling elevator or spaceship in free fall will feel the absence of gravity. But any difference in gravitational acceleration between his head and legs could easily tear his body apart. Tidal forces would be a death sentence near the stellar mass of a black hole, but pose no threat to the human body in the more expanded space around a supermassive black hole such as Sagittarius A *.
Accordingly, the density of matter required for the appearance of a black hole is in a linear relationship with its space-time curvature. Low mass black holes form when the core of a massive star collapses to densities well above that of an atomic nucleus. But for a supermassive hole, much more rarefied, it is enough to fill the orbit of Jupiter with liquid water. Sounds simple, but this engineering project is not feasible, as it would require an amount of water as large as 100 million suns. Well, the heat that would be released in the process of pouring water would burn all adjacent infrastructure facilities.
Indeed, the heat released during the compaction of a supermassive black hole poses a significant threat to civilizations that could be located in the center of galaxies. In our joint article with John Forbes, we showed that a significant part of the planets in the universe can lose their atmosphere and oceans, which can evaporate due to the fact that at some point in their existence they were near the galactic nucleus.
Promotional video:
For the first time in human history, we have the technology to capture images of supermassive black holes in the center of the Milky Way and the giant elliptical galaxy M87 against the backdrop of a luminous accumulation of gas behind them. The first such image will be published during the year.
In a 2018 lecture at the Black Hole Initiatives conference, an interdisciplinary center for black hole research at Harvard, I suggested that further progress in space propulsion could enable us to field studies of a nearby black hole. This will provide a great opportunity to try out one of the above activities - and perhaps exchange notes on quantum gravity with some tourists from other civilizations who have already camped there.
Abraham Loeb is Chair of the Department of Astronomy at Harvard University, Founding Director of the Harvard Black Hole Initiative, and Director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics. He also chairs the advisory board for the Breakthrough Stars hot project.