Unsolved Mystery

The world’s brightest scientists have spent decades searching for something they can’t see.

Scientists from NYU Abu Dhabi and around the world are working to gain an understanding of the dark components of the universe — the enigmatic dark energy and dark matter that theoretically permeate the universe, yet have never been detected.

More than 95 percent of our universe is made up of two unknown substances called dark energy and dark matter, explains Andrea Macciò, associate professor of physics and head of the physics program. “The first is responsible for the observed accelerated expansion of the universe, while the second is the glue that keeps galaxies together,” he said.

Macciò studies the impact different theoretical models of dark energy and dark matter have on observable properties of the universe and its main building block, the galaxies. “Since we cannot recreate a galaxy in a lab, I use complex computer simulations of galaxy formation to study galaxy evolution in a universe dominated by dark energy and dark matter,” he said.

His research has been aided over the past decade by the development of ever more powerful supercomputers: “What took months ten years ago can now be done in a few days, if not hours,” Macciò noted. What’s more, his field has benefited from more and better data provided by advanced terrestrial and space telescopes, such as the Atacama Large Millimeter Array, in Chile, and Gaia, a space observatory launched by the European Space Agency in 2013.

One thing that has evaded discovery, however, and would dramatically change the field, is empirical evidence of dark matter.

“I would love to see dark matter detected in a lab to directly confirm its existence,” Macciò said, “but that discovery depends on how nature has decided to create dark matter.”

Francesco Arneodo, associate dean of science and associate professor of physics, and Lotfi Benabderrahmane, lecturer of physics, are working on an international collaboration called XENON1T, that uses a highly specialized instrument to detect evidence of dark matter for the first time.

“Proving that dark matter exists, and knowing what it is made of, would mean that we could probe the majority of the matter of the universe, which would be an incredible step forward in our knowledge,” Arneodo explained.

Proving that dark matter exists, and knowing what it’s made of … would be an incredible step forward in our knowledge.

Francesco Arneodo

In order to have any hope of detecting dark matter, he goes on, one must create an instrument in which there are nearly no other interactions between particles. The instrument is buried deep under a mountain, beneath thousands of meters of rock in central Italy.

Everything is radioactive, Arneodo explained, and every square meter of the Earth is bombarded with hundreds of high-energy particles every second. “So if I want to create a detector that gets rid of all background radioactivity and only captures the signal that is left, I first have to go underground, under ice, or under the sea to shield my detector from cosmic rays and other particles,” he said. The next step is to shield the detector from the rock itself, and build it out of materials that give off the least possible amount of radiation.

The result is one cubic meter with the lowest amount of background radiation ever achieved on the planet, Benabderrahmane noted. The instrument is filled with liquefied xenon, which emits light when a subatomic particle interacts within it. If dark matter interacts with a xenon nucleus, the liquid will release photons and ionization electrons with a particular signature. Both components of the signal will be captured by specialized sensors called photomultipliers.

Scientists work with the XENON 1T device located in a special physics lab deep underneath a mountain in central Italy. It is the world's most sensitive tool to find dark matter. NYUAD is a collaborating institution on the experiment.

Once researchers know the mass and probability of the interaction of dark matter in relation to standard matter, researchers would be able to “study the properties of dark matter, and perhaps produce them in accelerators," Benabderrahmane said.

If Arneodo, Benabderrahmane, and their colleagues uncover dark matter below the mountain of Gran Sasso, more observations would need to be made to verify the discovery. But this finding “would indicate which theoretical model would be the right one,” and would allow other researchers in the field to pursue research programs that adhere to those particular models.