Physicists plan not to miss a single opportunity: whether dark matter affects different types of detectors, whether the light of the stars bends, whether the cores of the planets heats up and whether it is deposited in rocks.
Chart options mass of dark matter particles (clickable)
Since then, as in the 1980s it agreed that most of the mass in the universe is invisible to us, and that this "dark matter" should hold the galaxy from destruction and to form by gravity appearance of the whole cosmos The experimenters hunted for these non-luminous particles.
They first began looking for a heavy and slow form of dark matter called weakly interacting massive particles.(weakly interacting massive particle, WIMP) - wimps. This early candidate was one of the most preferable candidates for the role of lost cosmic matter - he could solve another, separate puzzle from particle physics. For decades, physicists have been building ever larger targets in the form of crystals and multi-ton reservoirs of exotic liquids, hoping to capture the rare flickering in atoms that occurs after the collision with WIMPs.
But detectors have remained silent, and physicists are increasingly beginning to speculate about a wider range of possibilities. On the more massive side of the spectrum, they say, the invisible matter of the Universe can clump , forming black holes weighing from a star. At the other extreme, dark matter can propagate as a thin haze of particles, thousands of trillion trillion times lighter than an electron.
New hypotheses bring with them new detection methods. Catherine Zurek, a theoretical physicist at the California Institute of Technology, says that if we don't see anything in the current WIMP experiments, "then a lot of research in this area will shift to these new experiments."
And the work has already begun. Here are a few of the many new frontiers in the search for dark matter.
Between an electron and a proton
Wimps would have enough mass to knock down whole atoms like a bowling ball. But in case the dark matter is lighter, in some experiments lighter pins are prepared.
A light rain of dark matter particles weighing less than a proton could sometimes knock electrons out of the atoms containing them. The first experiment designed specifically to capture such dark matter is the Sub-Electron-Noise Skipper CCD Experimental Instrument ( SENSEI ), which uses technology similar to that found in digital cameras. It amplifies signals from unexpectedly accelerated electrons that appear inside the substance.
When the SENSEI prototype was turned on, placing one-tenth of a gram of silicon in it, it did not find dark matter. Still, the results, published by the team in 2018, immediately ruled out certain models.
“As soon as we turned it on, we immediately got the best constraints in the world,” said Tien-Tien Yu , a physicist at the University of Oregon and a member of the SENSEI team. "Because there were no restrictions before."
Recent resultsThe two-gram version of the SENSEI experiment has expanded those limitations, and now Yu and his colleagues are preparing to implement the 10-gram version in an underground laboratory in Canada, away from interfering cosmic rays. Other groups are developing alternative low-cost versions of experiments aimed at similar, easily achievable results.
Towards relief
If dark matter is even lighter, or is not susceptible to electrical charges, it will not knock out electrons. Tsyurek brainstormed methods that would allow even such a small amount of her presence to be influenced by groups of particles.
Imagine a block of silicon in the form of a mattress, the springs of which are atomic nuclei. If you throw a small coin into such a mattress, says Tsyurek, then none of the springs will move too much. However, the coin will cause a wave that then travels through many springs. In 2017, she suggested that a similar disturbance caused by dark matter could generate sound waves that slightly heat the system.
One of the projects following this path, Tesseract, works now in the basement of the University of California at Berkeley. He searches for waves generated by dark matter particles, similar in weight to those that SENSEI is looking for. However, future versions of the experiment will theoretically make it possible to search for particles that are a thousand times lighter.
However, there are also more Lilliputian possibilities. Dark matter can be composed of axions - particles so light that they look more like waves than particles. It would also solve the riddle of the strong nuclear force. Recently, the Axion Dark Matter Experiment ( ADMX ) began looking for axions that decay into pairs of photons in a powerful magnetic field. Several other similar experiments are starting to work.
Some experiments are aimed at even lighter particles. The smallest mass that a dark matter particle can theoretically possess is a thousand trillion trillion times less than the mass of an electron. It would be a particle with an extremely low energy wave, and with a wavelength comparable to the diameter of a small galaxy. Even less weighty particles would be too smeared in space and could not explain why galaxies do not fall apart.
Hints from above
While some experimenters are preparing the next generation of devices, intending to establish direct contact with dark matter, others plan to comb the heavens in search of indirect signs of it.
It is believed that galaxies and stars create huge clouds of dark matter that gravitationally pull visible matter. However, if there are small clusters of dark matter, they would not be able to do this. These modest lumps would be completely dark, but would still bend the passing starlight. One group of researchers is looking for signs of this "lensing" of starlight by lumps of dark matter in the data from the Gaia Space Telescope, which is currently operating .
“Dark structures are moving through our galaxy,” said Anna-Maria Taki , a physicist at the University of Oregon and one of the group's members. "When they move, they distort the location, movement and trajectories of light sources."
Preliminary results , published in September, did not show the presence of such structures, the mass of which would be greater than 100 million suns. The researchers hope to have larger databases where smaller clouds can be found. And based on the size and shape of these hypothetical structures, scientists will already be able to understand how dark matter particles interact with each other.
Other researchers have figured out a way to accommodate the rapidly growing catalog of exoplanets for the search. “There are billions of these things,” said Rebecca Lin , a particle physicist at the SLAC National Accelerator Laboratory and co-author of the September proposal .
The idea is that a planet flying through the Milky Way could accumulate dark matter in its core. Particles of this dark matter, annihilating with their antiparticles, heat up the planet. Exoplanets closer to the center of the galaxy pass through denser clusters of dark matter, so they should glow brighter in the infrared range. Lin and colleagues calculated that if the future James Webb Space Telescope can measure the temperature of several thousand exoplanets, then in such a dataset it would be possible to consider signs of annihilation of dark matter particles, the mass of which is in the range between an electron and a proton.
Dark matter is everywhere
The Wimps may be in decline, but they have not yet been completely abandoned. Next March, the Gran Sasso National Laboratory in Italy will launch an experiment with a 4-ton xenon tank. South Korean team Cosine-100 wants to test a controversial claim made by participants in another experiment in Gran Sasso, DAMA. In the latter, an array of sodium iodide crystals recorded exactly the kind of seasonal changes in the data that should occur when the Earth puts different sides of the “wind” of dark matter through which it passes. “They have an annual modulation, no doubt about it. But where does it come from? " Said Catherine Fries , an astrophysicist at the University of Texas at Austin. "We cannot understand this."
Fries's calculations helped kick-start the era of WIMP experimentation. Now she has new ideas for finding these particles. In 2018, she suggested that wimps could be contained in rocks several kilometers deep, and she recently joined a proposal to dig them up.
Many physicists expect dark matter to be both apathetic and ubiquitous. If they can think of enough ways to sense the invisible, then its invisible influence can manifest itself anywhere. These methods include capturing different types of detectors, distorting starlight, heating the cores of planets, and even accumulating in stones.
“Anything can be a dark matter detector,” Lin said. "You just need to be creative enough to figure out how to use it."