The race to find dark matter is heating up

After finding "God's seeds", physicists rushed into a new race - searching for the dark matter, the material that was held between the keys of the movement of the galaxies. in the universe.

This year, the search for dark matter seems to dominate the minds of many physicists. This is an extremely attractive issue. We have gathered a lot of evidence of the gravitational force of dark matter in length, from single galaxies to galactic clusters - to the cosmic microwave background. These evidences are so diverse that it would be difficult to imagine any more appropriate answer to this law of universal gravitation with this "invisible" material .

Dark matter is very elusive.

However, dark matter is still very elusive. We will discuss in more detail later. But if we can detect dark matter, we will see them in a very close day.

Exploring the universe

So how do we detect dark matter? Francesca Calore from the University of Amsterdam (Netherlands) presented observational results of gamma ray and cosmic ray production. The idea here is that dark matter forms a halo of particles moving relatively slowly around galaxies, where these particles occasionally collide. When they bump into each other, matter particles are destroyed and produce a high-energy particle that we can detect. In some possible ways of decay, we get gamma rays along with / or cosmic rays.

The Euclid telescope is launched to find dark matter and dark energy.

Gamma rays are essentially the same as ordinary light rays, but they have very high energy. So they move through galaxies that are almost unimpeded. This means that we can adjust the probes towards the sky and note the energy, intensity and direction of the high energy gamma rays. These data can be used to compare predictions from astronomical sources we already know.

In fact, this work is much more complicated than we thought. First, you need to consider all possible gamma ray generation processes and eliminate those sources. You must then create a model of dark matter distribution and see if any of the observed redundant signals have a relationship with the predicted dark matter blocks.

Finally, you need to check the energy spectrum of gamma rays and see if they belong to the correct energy range and energy intensity (spectral shape) in accordance with what is expected from physical damage. dark or not.

All of this sounds strange. We do not know what dark matter is, then how to know exactly the range of energy that gamma rays need to have? Oh, the reality is not so. For example, we have a lot of particle physics data and many observations can eliminate all known energy bands. If excess energy occurs in the spectral region that we already know is not in the destruction of dark matter, they are false signals.

Comparing this information with what we already know, we see a signal source that is similar to that of dark matter. However, we still don't know all the gamma ray production processes. It is possible that a certain source of gamma rays appears to coincide with the hot spots we observe. These sources of gamma rays can come from astronomical objects like hidden galaxies that we didn't know during the observations of the universe.

The cluster of Abell 3827 clusters with green rings is believed to be the place where dark matter is present.

To eliminate this hypothesis, the team will focus radio telescopes on feasible sources and see if there is anything there. If nothing, then another theory is excluded. However, there are still many things to do.

In any case, every time we detect an abundance of cosmic rays, it is most likely due to dark matter. But the whole picture is much darker, because there are too many cosmic rays. If all were caused by dark matter, they would contradict measurements that excluded the possibility of dark matter. It is clear that in any case, we still have a lot of work to do, but this is really an exciting time.

Exploration on Earth

Many people spend time at the bottom of the mines deep in the ground, hoping to explore dark matter there. In this case, we rely on the fact that the Solar System is orbiting the Milky Way, with the plane of the system tilting at an angle to the galactic plane. As a result, our Earth plunges against the dark matter (if any) because the Sun pulls us around the galaxy with it. However, just like the Earth rotates around the Sun, we experience weak, strong, dark matter streams like the seasons on Earth.

"Dark matter wind (WIMP) blows in the opposite direction" when the solar system flies in the Milky Way.

This idea has become the subject of an extensive search, and the DAMA collaboration in Italy has confirmed dark matter discovery nearly a decade ago. Indeed, these signals are consistent that they have exceeded 9 standard deviations (in particle physics, only 5 standard deviations can be published in a new particle).

However, so far no other probes have detected this signal. Indeed, Laura Baudis came from Zurich University (Switzerland) with Patrick Decowski and Andrew Brown from Nikhef, Amsterdam presented the results of the XENON collaboration, showing that many of the possible explanations have been excluded. Dark matter for DAMA signals. Moreover, they also have a lot of data to analyze. However, the key will really be a type of independent verification. In order to provide these data, a copy of the DAMA experiment is being built in Antarctica.

Conflicting observations are not necessarily an argument at the present time. In the case of astrophysical detection, you need to eliminate a lot of background signals from these experiments.

Concept image of the solar plane deviation of the solar system with the Milky Way.

The basic idea behind these probes is that a dark matter particle can sometimes collide with other elementary particles. The echo of the collision signal can cause the following: heat emission, glowing if the nucleus suddenly moves faster than the local light speed (light travels in matter more slowly in a vacuum ), or luminescence by separating several electrons from atoms. All of these events can also be created by background radioactivity, cosmic rays in space and other unwanted elements.

Excluding these events requires not only understanding the frequency of occurrence, but also requiring the material you use to make these sensors respond to these different possibilities to be highly sensitive. That means the process has a rather high level of instability.The XENON probe was last operated to be dedicated to reducing these uncertainties.

The XENON partnership is on the verge of upgrading: researchers are increasing the size of the tools so they can hold 1 ton of xenon (a chemical element) in the probe cavity (previously 62kg xenon). ). At the same time, they also hoped to eliminate a large number of background signals. At the present time, one has recorded an event on 10kg of xenon each year, but they want to reduce them to 1 event per ton of xenon each year. That will be a remarkable achievement.

It will take more time for physicists to remove "noise" parameters from the results of observing dark matter.

More xenons, we will understand how the xenon reacts to more background radiation, reducing the signal noise level more. XENON cooperation program is looking forward to a bumper 2016 season. However, this is not the limit of ambition of researchers. They are still in the process of planning to upgrade XENON into a device that holds more tons of xenon. Finally, they want to be able to create the spectrum of dark matter, which requires 1 to 2 more upgrades. Big plans with bright future and require a lot of time.