37 minutes ago
Carlos Serrano (@carliserrano) BBC News Mundo
Photo credit, LZ/SURF
What is dark matter? The answer is simple: no one knows. This is one of the greatest puzzles in science.
Scientists have been searching for decades for clues to this mysterious component that makes up 25% of the universe.
But how do you look for something you don’t even know what it is, how do you find something that is invisible?
And if it’s so hard to find, why embark on such a complicated mission?
These questions inspired a team of more than 250 researchers from several countries, who recently published the first results of an ambitious project that hopes to finally find signs of dark matter.
This is LUX-ZEPLIN (LZ), a sophisticated laboratory located 1.5 miles underground in an abandoned gold mine in the town of Lead, South Dakota, USA.
The idea behind the underground location is to isolate the site as much as possible from radiation and dust, which can cause contamination that can hamper the search for dark matter.
Photo credit, N JEFFREY/ DARK ENERGY OBSERVATORY
It is the most detailed map of the distribution of dark matter in the universe. The bright areas represent the points of greatest concentration, where galaxies form.
According to its creators, the LZ is the most sensitive dark matter detector ever built.
To do this, they made the interior of the landing zone “the purest place on the planet”.
“The center of the detector is like the mind of a Buddhist monk,” Mundo Chamkaur Ghag, LZ researcher and professor in the department of physics and astronomy at University College London, UK, tells BBC.
The detector is designed to pick up even a faint signal from what might be a dark matter particle.
It’s like “listening intently in the middle of a silent field”, say the creators of the LZ on their website.
How does the LZ work, how does it search for dark matter, and what happens if it finds it?
The enigmatic dark matter
Right now we only know what 5% of the universe is made of. This 5% is ordinary matter, that which we can see or touch.
The particles that make up ordinary matter are described in what is known as the Standard Model.
The remaining 95% of matter is a mystery.
Photo credit, Getty Images
No one has seen dark matter, but its effects can be felt in the cosmos.
Physicists and astronomers suspect that of this percentage, 70% is dark energy and 25% dark matter.
Dark energy is a kind of repulsive force that accelerates the expansion of the universe.
Dark matter, on the other hand, is an invisible “something” that acts like a magnet holding galaxies together.
Astronomical observations have shown that galaxies rotate much faster than one would expect from their visible mass.
Calculations indicate that the gravity corresponding to this mass is not sufficient to hold the galaxies together. So there must be “something” that adds mass, and therefore extra gravity, and keeps them from hurtling through space.
That “something” that explains the extra gravity is dark matter.
It is said to be dark because it does not emit, reflect or absorb light, which makes it very difficult to observe.
That’s why, so far, the only sign scientists have of its existence is the gravitational effect that dark matter exerts on ordinary matter, such as stars and galaxies, for example.
Photo credit, LZ/SURF
The LZ laboratory is designed to detect dark matter.
So we don’t know what dark matter is, but without it the universe would be very different from what we know.
And what is dark matter made of?
Several ideas have been put forward for decades to explain what dark matter is made of, but there is still no convincing answer.
One possibility is that it is made up of “supersymmetric particles”, that is, hypothetical particles that associate with those that make up ordinary matter.
And there is another candidate to explain what dark matter is made of.
These are WIMPs, a hypothetical particle that the LZ hopes to detect.
According to NASA, WIMPs are the leading candidate for explaining dark matter.
WIMP stands for Weakly Interacting Massive Particle.
It is thought that WIMPs formed naturally following the Big Bang and that there must be so many of them that they might provide an explanation for dark matter.
These WIMPs are said to have the ability to permeate the universe and even pass through ordinary matter, but on rare occasions one of them might crash into the nucleus of an atom.
The LZ is looking for that exact moment…
Play billiards
The principle on which the LZ works is simple.
It is a titanium tank, filled with 10 tonnes of ultrapure liquid xenon.
The researchers chose xenon because, as a noble gas, it can be brought to very high levels of purification so that most pollutants can be removed.
The experiment consists of observing the particles traveling through the cosmos until they reach the center of the vessel.
With any luck, one of these particles will collide with the nucleus of one of the xenon atoms, like two billiard balls.
When this collision occurs, a burst of light is generated, which is detected by the LZ’s sensors.
After a collision, it is therefore a matter of analyzing the characteristics of the light generated and, from this analysis, deducing what type of particle has collided with the xenon atom.
Photo credit, LZ/SURF
The LZ is equipped with light sensors to detect particle collisions.
With the patience of a Buddhist monk, the LZ researchers hope that at some point it will be a WIMP that enters the vessel and collides with the nucleus of a xenon atom.
The LZ began its work in April, and in its first results published in early July, it has not yet detected traces of dark matter.
The purest place on the planet
One of the big challenges of the LZ is preventing unwanted particles from entering the tank to contaminate, confuse, or obscure a suddenly arriving WIMP.
The goal is to clear the whole scene for when the WIMP, if any, decides to show up.
Therefore, it is essential that the landing zone be underground.
Cosmic rays are constantly bombarding the planet’s atmosphere, creating particles that can hit a detector like the LZ and generate unwanted signals.
Photo credit, LZ/SURF
Two LZ researchers inspect possible dust particles in the xenon tank.
Being 1.5 km below ground prevents many of these particles from reaching the reservoir. Some may make it to the reservoir, but the odds are 10 million times lower.
Why look for dark matter?
Discovering dark matter would help us solve the problem of missing mass,” says Ghag.
“It’s the equivalent of understanding what nearly 30% of the universe is made of.
Ghag also mentions that “understanding or discovering dark matter would be the first window to look beyond the Standard Model, which is currently a closed room.”
The Standard Model is so far the best explanation of the particles and forces that make up ordinary matter.
However, this model only explains what regarding 5% of the universe is made of.
Another question that arises is whether, by detecting dark matter, we might exploit it as a source of energy.
Photo credit, LZ/SURF
Scientists in the LZ laboratory.
In this regard, the creators of the LZ claim that “it is unlikely that we will be able to harness the power of dark matter for centuries.”
“It’s unclear exactly how much benefit future generations will derive from mining dark matter, although these things tend to be remarkably unpredictable.
But in addition to the main mission of the LZ, the laboratory itself constitutes a breakthrough for science and technology.
Its beam and sensor analysis techniques can lead to innovations in the pharmaceutical food industry, and its system of algorithms can be used in fields such as nuclear medicine.
“But perhaps the greatest benefit to mankind is knowledge itself,” say the creators of LZ.
“We are a curious species, we seem to be programmed to want to know how the world around us works”.
