Can energy be sucked out of a black hole?
Can energy be sucked out of a black hole?
A rotating region is such an extreme force of nature that it drags surrounding time and space around with it. So it's only natural to ask whether black holes might be used as some kind of energy source. In 1969, mathematical physicist Roger Penrose proposed a way to try to to just this, now referred to as the "Penrose Process."
The method might be employed by sophisticated civilizations (aliens or future humans) to reap energy by making "black hole bombs." a number of the physics required to try to to so, however, had never been experimentally verified — so far . Our study confirming the underlying physics has just been published in Nature Physics.
Around its event horizon (the boundary around a region beyond which nothing, not even light, can escape), a rotating region creates a neighborhood called the "ergosphere." If an object falls into the ergosphere in such how that it splits — with one part falling into the region and therefore the other escaping — the part that flees effectively gains energy at the expense of the region . So by sending objects or light toward a rotating region , we could get energy back.
But does this theory hold up? In 1971, the Russian physicist Yakov Zel'dovich translated it to other rotating systems that would be tested back on Earth. The region became a rotating cylinder made up of a cloth which will absorb energy.
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Zel'dovich imagined that light waves could extract energy from the cylinder and become amplified. For the amplification effect to figure , however, these waves got to have something called "angular momentum," which twists them into spirals.
When twisted light waves hit such a cylinder, their frequency should change due to something called the "Doppler shift." you've got presumably experienced this when taking note of an ambulance siren. When it moves toward you it's a better pitch than when it moves faraway from you — the direction of travel changes the pitch of the sound. during a similar way, changes in rotational speed alter the perceived frequency of a light-weight wave.
If the cylinder rotates fast enough, the altered wave frequency should drop so low that it'll become negative (which simply means the wave spins within the opposite direction).
Positive frequency waves should be partly absorbed by the cylinder, losing energy. But the negative frequency waves would transform this loss into gain and instead become amplified by the cylinder. they might extract energy from the rotation, a bit like the thing escaping from Penrose's region .
Testing Zeldovich's theory may appear simple. But the rotating object must spin at an equivalent or higher frequency because the waves. To amplify light waves, which oscillate at a frequency of many trillions of times a second, you'd got to rotate an absorbing object billions of times faster than anything that's mechanically possible today.
Breakthrough eventually
Light travels at about 300 million meters per second. So to form the idea easier to check , we opted to use sound waves, which travel roughly 1,000,000 times slower, meaning we didn't need the absorber to rotate so quickly.
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To create a twisted acoustic wave , we used a hoop of speakers all emitting an equivalent frequency but starting at slightly different times, therefore the sound follows a spiral. For our rotating absorber we used a bit of sound-absorbing foam attached to a motor. Microphones placed inside the froth allowed us to record the sound after it had interacted with the rotating absorber.
We found that when the froth span slowly (at a coffee frequency), the sound we recorded was quieter because it had been absorbed by the froth . But once we spun the froth fast enough for it to Doppler effect the frequency of the sound waves enough to form them negative, the sound became louder.
This can only mean that the acoustic wave had taken energy from our rotating absorber, finally proving the 50-year-old
A rotating region is such an extreme force of nature that it drags surrounding time and space around with it. So it's only natural to ask whether black holes might be used as some kind of energy source. In 1969, mathematical physicist Roger Penrose proposed a way to try to to just this, now referred to as the "Penrose Process."
The method might be employed by sophisticated civilizations (aliens or future humans) to reap energy by making "black hole bombs." a number of the physics required to try to to so, however, had never been experimentally verified — so far . Our study confirming the underlying physics has just been published in Nature Physics.
Around its event horizon (the boundary around a region beyond which nothing, not even light, can escape), a rotating region creates a neighborhood called the "ergosphere." If an object falls into the ergosphere in such how that it splits — with one part falling into the region and therefore the other escaping — the part that flees effectively gains energy at the expense of the region . So by sending objects or light toward a rotating region , we could get energy back.
But does this theory hold up? In 1971, the Russian physicist Yakov Zel'dovich translated it to other rotating systems that would be tested back on Earth. The region became a rotating cylinder made up of a cloth which will absorb energy.
Advertisement
Zel'dovich imagined that light waves could extract energy from the cylinder and become amplified. For the amplification effect to figure , however, these waves got to have something called "angular momentum," which twists them into spirals.
When twisted light waves hit such a cylinder, their frequency should change due to something called the "Doppler shift." you've got presumably experienced this when taking note of an ambulance siren. When it moves toward you it's a better pitch than when it moves faraway from you — the direction of travel changes the pitch of the sound. during a similar way, changes in rotational speed alter the perceived frequency of a light-weight wave.
If the cylinder rotates fast enough, the altered wave frequency should drop so low that it'll become negative (which simply means the wave spins within the opposite direction).
Positive frequency waves should be partly absorbed by the cylinder, losing energy. But the negative frequency waves would transform this loss into gain and instead become amplified by the cylinder. they might extract energy from the rotation, a bit like the thing escaping from Penrose's region .
Testing Zeldovich's theory may appear simple. But the rotating object must spin at an equivalent or higher frequency because the waves. To amplify light waves, which oscillate at a frequency of many trillions of times a second, you'd got to rotate an absorbing object billions of times faster than anything that's mechanically possible today.
Breakthrough eventually
Light travels at about 300 million meters per second. So to form the idea easier to check , we opted to use sound waves, which travel roughly 1,000,000 times slower, meaning we didn't need the absorber to rotate so quickly.
Advertisement
To create a twisted acoustic wave , we used a hoop of speakers all emitting an equivalent frequency but starting at slightly different times, therefore the sound follows a spiral. For our rotating absorber we used a bit of sound-absorbing foam attached to a motor. Microphones placed inside the froth allowed us to record the sound after it had interacted with the rotating absorber.
We found that when the froth span slowly (at a coffee frequency), the sound we recorded was quieter because it had been absorbed by the froth . But once we spun the froth fast enough for it to Doppler effect the frequency of the sound waves enough to form them negative, the sound became louder.
This can only mean that the acoustic wave had taken energy from our rotating absorber, finally proving the 50-year-old
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