Through years of research, it became clear that dark matter behaves abominably. This term was introduced about 80 years ago by astronomer Fritz Zwicky who realized that in order to prevent individual galaxies to escape in a gigantic galactic clusters, some of the gravitational force. Later Vera Rubin and Kent Ford used invisible dark matter to explain why galaxies do not fly.
However, although we use the term “dark matter” to describe these two situations, it is unclear whether involved in each of them the same culprit. The simplest and most popular model says that dark matter consists of weakly interacting particles that move slowly under the force of gravity. This so-called “cold” dark matter describes large scale structures such as clusters of galaxies. But it is bad with predicting rotation curves of individual galaxies. Dark matter is like different acts on the same scale.
In an attempt to resolve this puzzle, two physicist recently suggested that dark matter can change phase when you change the scale. Justin Hori, a physicist at the University of Pennsylvania, and his former PhD student Lasha, Berezhiani working at Princeton University, says that in cold and dense environment of the galactic halo dark matter condenseries in the supercritical liquid is an exotic quantum state of matter with zero viscosity. If dark matter forms a supercritical fluid in a galactic scale, may be a new force, which would explain the observations that do not fit the model of cold dark matter. But the scale of galactic clusters the special conditions required for the formation of the supercritical state, does not exist; here the dark matter will behave as ordinary cold dark matter.
“It’s a great idea,” says Tim Tait, particle physicist from the University of California, Irvine. “Two different types of dark matter describes one thing.” And soon this curious idea you can check. Although other physicists have already considered these ideas, Hori and Berezhiani close to extract verifiable predictions that would allow astronomers to explore, swim, whether our galaxy in a sea of supercritical fluid.
Impossible superfluids
On Earth overcriticize liquid you can’t call something mediocre. But physics are prepared in their laboratories in 1938. Cool the particles to a sufficiently low temperature, will manifest their quantum nature. They will begin to worry, and the waves will overlap, until eventually begin to behave like one big “swashata”. They become coherent, like the particles of light in the laser that have the same energy and vibrate as one. In our days, even students are condensates Bose — Einstein in the laboratory, many of which can be classified as a supercritical fluid.
Phenomena of superfluidity in the everyday world does not exist — too warm, in order to manifest the desired quantum effects. Because of this, “ten years ago people just would have refused this idea and said that it is impossible,” says Tate. But in recent years more and more physicists are coming to believe that supercritical phases are formed naturally in the extreme conditions of space. Superfluidity may be in neutron stars, and the very space-time, according to some, may be a supercritical fluid. Why would dark matter not to be such?
To make the set of particles by supercritical fluid, it is necessary to fulfill two conditions: packaging of the particles with high density and cool them to extremely low temperatures. In the physics lab (or student), limit of a particle in an electromagnetic trap, and then irradiated with laser to remove kinetic energy and lower the temperature to near absolute zero.
Inside galaxies, the role of the electromagnetic trap will play the gravitational pull of a galaxy, which will compress the dark matter is enough to satisfy the criterion of density. With the temperature simpler in space is very cold.
Outside of the halo are detected in the vicinity of galaxies, gravity is weaker, and the dark substance will not be Packed tight enough to go into the supercritical state. She will act like regular dark matter, explaining what astronomers see on a large scale.
In rotating superfluid helium formed a small vortex
But what’s so special about that dark matter is a superfluid? As a special condition to change behavior of dark matter? In recent years, many scientists have thought about this issue. But the approach of Hori unique because it demonstrates how superfluidity could give rise to a new force.
In physics, if you break the box, you create a wave (often). Shake a few electrons, e.g., in antenna and you violate the electric field and receive radio waves. Alarm gravitational field of two colliding black holes — and receive gravitational waves. Similarly, if you push overheadcosts, you will produce phonons — sound waves in superfluid itself. These phonons give rise to an additional force in addition to gravity, the same electrostatic force between charged particles. “That’s good, because you have more power over gravity, while internally tied to dark matter,” says Hori. “It is an environment property of dark matter gives rise to this force.” It could explain the strange behaviour of dark matter in the galactic halo.
Even one particle of dark matter
Hunters on dark matter searching for her for a long time. Their efforts were concentrated on the so-called weakly interacting massive particles, or WIMP. WIMP was popular because these particles not only could explain the majority of astrophysical observations, but also come naturally from the hypothetical extensions of the Standard model of particle physics.
However, no one has ever seen a WIMP, and these hypothetical extensions of the Standard model didn’t show in the experiments, much to the dismay of physicists. With each new zero-sum prospects brood more and more, and physics are increasingly considering other candidates for dark matter. “At what point should we decide that barking up the wrong tree?”, asks Stacy Makkah, an astronomer at the University of Case Western Reserve.
Dark matter particles, which implies the work of Hori and Berezhiani, strongly similar to WIMP. WIMP needs to be pretty massive for a fundamental particle — about 100 proton masses. To load the script, houri, dark matter particles must be a billion times easier. Accordingly, the Universe will be billions of times more — and that’s enough to explain the observed effects of dark matter and to achieve the density required for the formation of the supercritical fluid. In addition, the usual WIMP does not interact. But superfluid dark matter particles will strongly interact.
The closest candidate is the axion, a hypothetical ultralight particle with a mass that can be 10,000 trillion trillion times smaller than the mass of the electron. In the words of Chanda Prescod-Weinstein, theoretical physicist at the University of Washington, axions could theoretically condense in the condensate Bose — Einstein.
But the standard axion does not entirely satisfy the needs of Hori and Berejiani. In their model, the particles should experience a strong repulsive interaction. Typical models of axions interact weakly and attracting. By the way, “I think everyone believes that dark matter interacts with itself at a certain level,” says Tate. We only need to understand the strong or weak interaction.
In search of cosmic superfluidity
The next step for Hori and Biriyani will be figuring out how to test their model is to find the little signature that could distinguish the concept of the supercritical fluid from the usual cold dark matter. One possibility: the vortices of dark matter. In the laboratory rotating supercritical fluid give rise to twisted vortices, which continue without losing energy. Halo superfluid dark matter in the galaxy must rotate fast enough to create arrays of vortices. If these vortices were massive enough, they could be detected directly.
Unfortunately, this is unlikely: the latest computer models, Hori show that vortices in a superfluid dark matter are “pretty flimsy” and unlikely to exist in reality. He suggests that it would be possible to use the phenomenon of gravitational lensing to see any effects of scattering, similar to how the crystal scatters the x-ray passing through it the light.
Astronomers could also look for indirect evidence that dark matter behaves as a supercritical fluid. To this end, they will study the mergers of galaxies.
The speed at which galaxies collide among themselves, is determined by the dynamic friction. Imagine a massive body passing through a sea of particles. Many smaller particles will be attracted massive body. And since the total momentum of the system does not change, the massive body needs will slow down to compensate.
This happens when two galaxies begin to merge. If they get close enough, the halo of their dark matter will begin to pass one through the other, and the rearrangement of independently moving particles will lead to dynamical friction, pulling halo closer. This effect helps galaxies to merge and stepping up the pace of mergers of galaxies in the Universe.
But if halo dark matter were in a state of supercritical fluid, the particles would move synchronously. And there would be friction, closer galaxy, it would be difficult to merge. All this would have amounted to an eloquent picture of the fluctuations of the interference patterns in the distribution of matter in galaxies.
Acceptable wonders
Although Makkah a positive attitude to the idea of a superfluid dark matter, he admits that trying so hard to combine the best of both concepts, physics can come to a “decision of Tycho Brahe”. Danish astronomer of the 16th century invented the hybrid cosmology in which the Earth was the center of the Universe, but all other planets revolved around the Sun. He tried to draw a line between the ancient Ptolemaic system and the Copernican cosmology, which eventually replaced it. Maybe the scientists are missing something fundamental. But the idea is worth consideration.
Tate believes the new model is beautiful in General, but wish she was more specific at the microscopic level, to such an extent that “we can calculate and show why it all works as it should work. Only need a few miracles” that everything fell into place. Perhaps these miracles are quite valid, but he’s not sure.
Although scientists experimented with superfluid many decades of particle physics are only beginning to fully understand the usefulness of the ideas emerging from the field of condensed matter physics. By combining this physics with gravitational physics, to resolve long-raging question of dark matter and who knows what other breakthroughs we are waiting for?
“Do I need a superfluid model? Not quite, says Prescod-Weinstein. — But the universe can do. It can in a natural way to form the condensates a Bose — Einstein condensate, as the masers is naturally formed in the Orion nebula. Do I need masers in space? No, but they’re cool.”
Recipe of dark matter can include a supercritical fluid
Ilya Hel