Thanks to their enormous gravitational forces, the regions around black holes are violent and turbulent environments driven by physics that cannot be found anywhere else in the universe. In fact, black holes are so effective that when they rotate, they drag the fabric of space with them. In other words, nothing remains stationary near a black hole. Nothing.
Obviously, black holes cannot drift into Earth, so these effects can be studied in the laboratory; But a research team led by University of Nottingham scientists did the next best thing. For the first time, researchers have created a spinning “quantum vortex” in a helium superfluid cooled to ultracold temperatures. This apparatus actually simulates a black hole on our planet.
This is because the quantum tornado produces tiny waves on the surface of a superfluid, a material that can exhibit frictionless flow (or incredibly low viscosity) and other exotic behaviors observed at temperatures near absolute zero. These are behaviors that mimic conditions found near spinning black holes.
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“Using superfluid helium allowed us to study small surface waves in more detail and accuracy than our previous experiments in water,” team leader and University of Nottingham researcher Patrik Svancara said in a statement. said. “Because the viscosity of superfluid helium is extremely small, we were able to rigorously investigate their interaction with the superfluid tornado and compare the findings with our own theoretical projections.”
Whirling space-time tornadoes
To understand how a superfluid vortex might resemble a black hole, it is vital to remember what Einstein’s 1915 theory of general relativity tells us about black holes. General relativity proposes that space and time are a single entity called spacetime, and that gravity arises when massive objects cause space-time to warp.
Black holes are not actually objects, but regions of space-time created by an infinitely dense and compact mass; A central singularity where the laws of physics break down. The outer boundary of these space-time regions is called the event horizon and represents the point at which even light is too fast to keep up with the black hole’s escape velocity.
Black holes have only three known properties: electric charge, mass, and angular momentum or “spin.” A spinning black hole, or a “Kerr black hole” with angular momentum, drags the space-time fabric with it in the direction of its rotation; This is an effect known as “frame dragging” or, as scientists explain it, the Lense-Thirring effect. Who first suggested this?
Considering the Lense-Thirring effect and how the forces around the Kerr black hole are important in constant motion, it makes sense that a vortex in a liquid, or perhaps a hurricane in the atmosphere, would very loosely resemble such a region of spacetime. But the most important feature of the team’s black hole simulation vortex is that it is not found in any ancient liquid. It was made in a superfluid cooled to absolute zero.
To conduct their experiments, the team built a special cryogenic system that could hold several liters of helium and cool it to temperatures below minus 456 degrees Fahrenheit (minus 271 degrees Celsius). This is approximately 3 to 4 degrees above absolute zero and equals minus 459.76 degrees Fahrenheit (minus 273.15 degrees Celsius). Absolute zero is the coldest theoretically possible temperature. At absolute zero all atomic motion stops.
At the temperatures reached by the experiment, liquid helium develops quantum properties that generally prevent the formation of giant eddies. This system showed how this cannot actually be solved; The team ultimately constructed a quantum tornado in ultracold superfluid using many tiny pieces.
“Superfluid helium contains tiny objects called quantum vortices that tend to drift apart from each other,” Svancara continued. “In our setup, we managed to confine tens of thousands of these quanta into a compact object resembling a small tornado, resulting in a vortex flow of record-breaking strength in the field of quantum liquids.”
Svancara and his colleagues found fascinating parallels between quantum whirlwinds and the way black holes’ gravity affects spacetime. The team hopes that the experiment will open a way to simulate quantum physics more broadly in curved spacetime in general, and even around black hole curved spacetime.
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“When we first observed clear signs of black hole physics in our first analog experiment in 2017, it was a groundbreaking moment for understanding some strange phenomena that are often difficult, if not impossible, to study otherwise,” said lead author Silke Weinfurtner. In the statement, the status of the Black Hole Laboratory, where this experiment was developed and carried out, was explained.
“Now,” Weinfurtner continued, “we have taken this research to the next level with our more complex experiments, which may eventually enable us to predict how quantum fields behave in the curved spacetimes around astrophysical black holes.”
The team’s research was published in the journal Nature on Wednesday, March 20.