This photo, recently released by NASA’s Chandra X-ray Observatory, shows black holes in a portion of the sky about two-thirds the diameter of the full moon seen at night. Chandra collected x-ray data from this small patch of sky for the equivalent of two months and then the data was “stacked” to produce the most detailed x-ray astronomy image ever. The photo shows more than one thousand supermassive black holes—the kind thought to exist at the center of galaxies—in just that small patch of sky. If that zone is typical of the rest of the sky, it means there are more than a billion such black holes out there. But before you get too worried, most of the black holes pictured are close to thirteen billion light years from Earth, meaning not only that they’re much too far away to worry about, but also that the image of them we’re seeing is from thirteen billion years in the past. A billion years or less after the Big Bang that produced the universe itself. Who knows what state they’re in now?
Black holes form when stars with at least three times the mass of our sun burn out and collapse in upon themselves. The material packs so densely together that the result is a fantastic amount of mass in a relatively small area, called a singularity, and within a certain distance of that singularity the force of its gravity is so strong that nothing, not even light, can escape it (explaining why it’s black!) That point-of-no-return is called the black hole’s event horizon because nothing can be seen beyond it. But the event horizon is also a zone of intense radiation, and often jets of radioactive particles stream outward from it, which scientists can see in the x-ray spectrum.
The thought of billions of black holes (possibly thousands in our galaxy alone) is rich fodder for the imagination. Think of what could be done with them! Borrowing the ideas of various science fiction writers, what if black holes are:
Shortcuts through space/time—these are called wormholes, but some physicists suggest that you could have a wormhole with black holes, like doorways, at each end. Could we use them to travel to far distant places? Well, somehow we’d have to survive the unthinkable gravity and tidal forces, radiation, and other unknown hazards, plus we’d still have to have incredibly fast spaceships to even get to the nearest black hole in the first place. Otherwise…maybe.
Doorways to another universe—but, if so, how will we ever know? Nothing is powerful enough to come back through one.
Portals for traveling into the past—if you could somehow manipulate black holes at the mouths of wormholes, theoretically you could place one at an earlier location in space/time. But then if we had the engineering ability to move black holes around, we could probably do anything we wanted with space/time anyway.
Means to jump into the future—as in the movie Interstellar, being close to a black hole slows your perception of time. Get close enough to a black hole for a few minutes and decades might have passed in the universe at large. A quick trip to the future, yes, but no way to return to your own time to tell about it.
Weapons—locate and manipulate a small black hole, then use it to eat your enemy’s city, or planet, or solar system. Hmmmm, except a black hole would just as happily gobble you as the bad guys. I also think they’d be kind of hard to sneak past galactic security.
Power sources—Star Trek’s Romulans use black holes to power their starships. Mind you, using something that can warp space/time is bound to produce some undesirable side effects, not to mention that if the containment field fails the thing will consume your ship like a fistful of nachos on Superbowl Sunday.
Prisons—in a re-visioning of an Arthur C. Clarke novel, Gregory Benford imagined using a black hole as a prison for an immensely powerful and evil intelligence. Something that you can’t destroy any other way? Yup, I guess that would work. Unless the black hole turns out to be a gateway to another universe, another place in your own universe, or another time, in which case you’ve just shifted the problem.
Personally, I’ve sometimes wondered if black holes—the most destructive forces in our universe—spend billions of years gathering matter and energy because, at the right moment, they’ll suddenly explode in a Big Bang that creates a whole new universe in a different dimension—literally the mothers of all space phenomena.
I don’t know what physics would say about that, but it feels rather poetic to me.