Recipe dark matter may comprise supercritical fluid
Through years of research, it became clear that the dark matter behaves abominably. This term was introduced about 80 years ago, astronomer Fritz Zwicky, who realized that in order to keep the run of individual galaxies in a giant galaxy clusters, you need some kind of gravitational force. Later Vera Rubin and Kent Ford used the 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 which move slowly under the influence of gravity. This so-called "cold" dark matter accurately describes the large-scale structures such as clusters of galaxies. But it is well short of predicting individual rotation curves of galaxies. Dark matter if differently acts in such scales.
In an attempt to solve this puzzle, recently two physicists have suggested that dark matter can change when you change the scale of phase. Justin Khoury, a physicist at the University of Pennsylvania, and his former graduate student Lasha Berezhiani working at Princeton University, said that in the cold and dense environment of the galactic halo dark matter condensed into a supercritical fluid - exotic quantum state of matter with zero viscosity. If dark matter forms a supercritical fluid on a galactic scale, there may be a new force, which would explain the observations that do not fit into the model of cold dark matter. But the scale of galactic clusters of special conditions necessary for the formation of the supercritical state, does not exist; Here dark matter behaves like a normal cold dark matter. "It's a great idea," said Tim Tait, particle physicist at the University of California at Irvine. "Two different types of dark matter described by the same thing." And soon this interesting idea can be tested. While other physicists have already seen similar ideas, and Khouri Berezhiani close to having to extract testable predictions, which would allow astronomers to investigate, whether our galaxy floats in a sea of a supercritical fluid.
Impossible superfluid liquid
On Earth sverkriticheskie liquid can not be called something ordinary. But physicists prepare them in their laboratories since 1938. Cool the particles to a sufficiently low temperature, and begin to manifest their quantum nature. They will worry, and the waves will overlap until eventually begin to act like one big "superatom". They will be coherent, like particles of light in a laser, which has one energy and vibrate as one. Nowadays, even the students create Bose - Einstein condensates in the laboratory, many of which can be classified as a supercritical fluid.
Superfluidity phenomena in the everyday world does not exist - too warm, so that we can manifest the desired quantum effects. Because of this "Ten years ago, people would have simply refused the idea and said it was impossible," says Tate. But lately, more and more physicists are coming to believe that supercritical phases are formed naturally in the extreme conditions of space. Superfluidity can be inside neutron stars, and the space-time itself, according to some, may be a supercritical fluid. Why not be the dark matter itself?
To make a set of supercritical fluid particle, two conditions must be met: pack particles with high density and cool them to an extremely low temperature. Physics Laboratory (or students) bound particles in an electromagnetic trap, and then irradiated with a laser to remove the kinetic energy and reduce the temperature to near absolute zero. Inside galaxies role of electromagnetic traps will play the gravitational pull of the galaxy, which will compress the dark matter is sufficient to meet the criterion of density. With the temperature easier: in space it is very cold.
Outside halo, which are found in the immediate vicinity of galaxies, gravity is weaker, but the dark matter is not packed tightly enough to go into a supercritical state. It will operate as a normal dark matter, explaining that astronomers see a large scale.
small eddies are formed in rotating superfluid helium
But what's so special about that dark matter will a superfluid? As a special condition will change the behavior of dark matter? In recent years, many scientists have thought about this issue. But Khouri approach is unique because it shows how superfluidity could give rise to a new force.
In physics, if you break the box, you create a wave of (often). Shake several electrons - for example, in the antenna - and you break the electric field and radio waves get. Alarm gravitational field of two colliding black holes - and get gravitational waves. Similarly, if you will push sverhzhidkost, you will generate phonons - sound waves in superfluid itself. These phonons give rise to additional force in addition to gravity, similar to the electrostatic force between charged particles. "That's good, because you have an additional force of gravity on top, while internally linked to dark matter," says Khouri. "It is this environment property of dark matter giving rise to this force." It could explain the strange behavior of the dark matter in the galactic halo.
Another dark matter particles
Hunters in the dark matter search for it for a long time. Their efforts have focused on the so-called weakly interacting massive particle, or WIMP. WIMP were popular because these particles could not only explain the majority of astrophysical observations, but also come naturally from the hypothetical extensions of the Standard Model of particle physics.
However, nobody has ever seen of WIMP, and the hypothetical extension of the Standard Model also does not show up in experiments, much to the dismay of physicists. With each new zero-sum perspectives brood more, and physicists are increasingly considering other candidates for dark matter. "At what point do we decide that barking up the wrong tree?" Asks Stacey Makgoh, an astronomer at Case Western Reserve University.
Particles of dark matter, which involves work Khouri and Berezhiani, decidedly not like the WIMP. WIMP should be pretty massive for fundamental particles - approximately 100 proton masses. To load a script Khouri, dark matter particles must be a billion times easier. Accordingly, in the universe there will be billions of times more - and this is enough to explain the observed effects of dark matter and reach the density required for the formation of a supercritical fluid. Furthermore, conventional WIMP not interact. But superfluid particles of dark matter would have to interact strongly.
The closest candidate is axion, hypothetical ultralight particle mass, which may be of 10 000 trillion trillion times less than the electron mass. According to Chanda Prescod-Weinstein, a theoretical physicist at the University of Washington, axions could theoretically condense in Bose - Einstein condensate. But the standard axion does not entirely satisfy the needs and Berezhiani Khouri. In their model, the particle must experience a strong repulsive interaction between them. Typical model axions interact weakly and Attracting. By the way, "I think everybody thought that dark matter interacts with itself at a certain level," says Tate. It is only necessary to understand this is a strong or weak interaction.
In search of space superfluidity
The next step for Khouri and Berezhiani will be figuring out how to check their model - found speaking signature that would distinguish the concept of a supercritical fluid from the usual cold dark matter. One possibility: eddies of dark matter. In the laboratory rotating supercritical fluid generate swirling vortices that are going on, without losing energy. Superfluid halo of dark matter in the galaxy must rotate fast enough to create a vortex arrays. If these vortices were massive enough, they can be detected directly.
Unfortunately, this is unlikely: the latest computer models Khouri show that vortices in superfluid dark matter will be "pretty shaky" and are unlikely to exist in reality. He suggests that one would use a phenomenon of gravitational lensing to see any effects of scattering, just as the crystal scatters the X-ray passing through the light.
Astronomers could also look for indirect evidence that dark matter behaves as a supercritical fluid. To this end, they will examine the merger of galaxies.
The rate at which galaxies collide with each other, determined by the dynamic friction. Imagine a massive body, passing through the sea of particles. A plurality of smaller particles will be attracted massive body. And since the total momentum of the system does not change, a massive body has to slow down a bit to compensate. This happens when two galaxies begin to merge. If they come close enough, a halo of dark matter will begin to take place one after another, and the rearrangement of independently moving particles will lead to dynamic friction, pulling halo closer. This effect helps galaxies to merge and the steps up merger of galaxies in the universe.
But if dark matter halo was able supercritical fluid particle would move synchronously. And there would be no friction, moving closer galaxy, it would be difficult to blend. All this would amount to an eloquent picture: fluctuations in the interference patterns in the distribution of matter of galaxies.
Although Makgoh positively to the idea of a superfluid dark matter, he admits that trying so hard to combine the best of both concepts of 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 the other planets revolved around the sun. He tried to draw a line between the ancient Ptolemaic system and the Copernican cosmology, which will eventually replace it. Perhaps scientists are missing something fundamental. But the idea is worth considering.
Tate says the new model a great overall, but would like to see it focus the microscopic level, to such an extent that "we can all calculate and show why it all works as it should work. Only need several miracles, "so that all fell into place. Perhaps these miracles are quite acceptable, but he is not sure.
Although scientists have experimented with superfluid many decades, particle physicists are only beginning to be fully aware of the usefulness of the ideas emerging from the field of condensed matter physics. By combining this with the physics of gravitational physics could be solved long-raging question of dark matter - and who knows what other breakthroughs are waiting for us? "Do I need superfluid model? Not really - says Prescod-Weinstein. - But the universe can do it. It may naturally form condensates Bose - Einstein as masers naturally formed in the nebula Orion. Do I need masers in space? No, but they're fun. "