Sunday, October 17

Dark matter: one last push to decipher the greatest secret in the universe | Space


DDeep underground, scientists are closing in on one of modern science’s most elusive targets: dark matter. In underground laboratories in the US and Italy, they have installed huge vats of liquid xenon and lined them with high-sensitivity detectors in hopes of detecting subatomic collisions that reveal the presence of this elusive material.

However, the researchers acknowledge that the current generation of detectors is reaching the limit of their effectiveness and warn that if they do not detect dark matter with these types of machines, they could be forced to completely reevaluate their understanding of the cosmos.

“Dark matter represents about 85% of all the mass in the universe, but so far we have not been able to detect it, despite having built increasingly powerful detectors,” said physicist professor Chamkaur Ghag of University College London. “Now we are approaching the limits of our detectors and if they do not find dark matter in the next few years, we may have to accept that there is something very wrong with the way we think about the universe and gravity.”

The search for dark matter began last century when astronomers discovered that galaxies appeared to be spinning too fast to remain stable. Observations indicated that they must have masses 10 times greater than their visible content (stars, planets, and dust clouds), otherwise they would break apart.

Professor Chamkaur Ghag
Professor Chamkaur Ghag: ‘It could be that we are looking for our keys under the lamppost. Dark matter could be a lot weirder than we’ve assumed so far. Photograph: John Gaffen / Alamy

The missing material that generates the extra gravity needed to hold the galaxies together was called “dark matter.” Astronomers initially thought that it could be made up of stars too small or faint to be seen from Earth or by other candidates, such as neutron stars. However, newer generations of powerful telescopes showed that these were not viable possibilities.

So scientists went from astronomically large to incredibly small to explain the missing mass of the universe. Large numbers of undetected particles form invisible halos around galaxies and increase their gravitational fields, they argued. These hypothetical particles are called weaklings, massive particles that interact weakly, and researchers have struggled to detect them for two decades.

These efforts have involved building detectors deep underground where they are shielded from subatomic particles, triggered by cosmic rays hitting the upper atmosphere that constantly fall on Earth and would trigger streams of false positive readings on their instruments.

“The expectation has been that a wimp will hit a xenon core and the resulting flash of light will be detected by a detector and thus reveal the presence of a dark matter wimp,” Ghag said. “However, despite years of effort, we have yet to see a single flash like that. We need more sensitivity. “

Now researchers are pinning their hopes on the two most sensitive wimp hunters ever designed. One, built under the Gran Sasso mountains of Italy, is known as XENONnT. The other, Lux-Zeplin, has been built on a former South Dakota gold mine. Both devices have been filled with several tons of xenon, far more than has been put into any previous device, and that should increase the chances of a wimp hitting a core.

Ghag, a member of the Lux-Zeplin team, said: “Both devices are now undergoing operational tests and in a few months those tests will be completed. We may find that we have detected dark matter during that period, which would be very good news. Otherwise, both devices will run without interruption for several years. Essentially, the more xenon we have in our machines and the longer we run our detectors, the better our chances are for collisions to occur and for dark matter to reveal its presence. “

However, it is now accepted that there is a possibility that this will not happen and dark matter could still be elusive. As Mariangela Lisanti, a physicist at Princeton University in New Jersey, said in the magazine Science recently: “The weakling hypothesis will face its true reckoning after these next-generation detectors are run.”

The Lux-Zeplin detector
The Lux-Zeplin detector is sealed before being placed underground.

If Lux-Zeplin and XENONnT don’t find Wimps, the two teams of scientists will have one last chance to use current technology to find them, joining forces to create a final super-large detector that would contain tens of tons of xenon, a rare and expensive gas to isolate. , and that it would work for several years.

And if that last-chance detector fails to find dark matter, scientists would be stumped. Making their machines even more sensitive would result in them being inundated with signals triggered by another type of subatomic particle, the neutrino, which rains down on Earth in billions of dollars every second. Other approaches should be taken.

“It could be that when looking for the weak, we are looking for our keys under the lamppost,” Ghag added. “Dark matter could be a lot weirder than we’ve assumed so far. It could be made up of small black holes. Or it could be made of something a million times lighter than a wimp and spotting it will be very difficult. So we will have to be much more sophisticated in our detection attempts. “

Such efforts to find a form of matter that can barely interact with normal matter may seem unnecessary. But if it weren’t for the pervasive gravitational influence of dark matter, galaxies, stars, and planets would not have been held together in the early universe and life as we know it would not have evolved. Hence, scientists continue their efforts to discover its true nature.


www.theguardian.com

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