Scientists have long known that something is missing in our understanding of the universe.
About 85% of the matter in the cosmos is invisible and mysterious.
This “dark matter” doesn’t emit light or energy, so we can’t see it directly. However, we know it’s there because of the way it affects the things we can see, like stars and galaxies, through its gravitational pull.
A team of around 250 scientists from across the globe, including myself, has been working on a dark matter experiment called LUX-ZEPLIN (or LZ). Our mission is to discover exactly what this dark matter is made of.
While we haven’t found the dark matter particles yet, we’ve made some exciting progress.
Our latest research sets new limits on what these particles could be, and we’ve confirmed that our detector is working well. This means we’re getting closer to uncovering the secrets of dark matter.
What Exactly is Dark Matter?
When astronomers observe the universe, they notice that visible matter, like stars and gas, doesn’t fully explain what they see. For instance, galaxies spin at speeds that suggest there’s much more mass than what’s visible. Also, the afterglow of the Big Bang, the event that created the universe, shows patterns that imply the existence of large amounts of invisible matter—this is what we call dark matter.
But what is dark matter made of? Currently, we don’t have a clear answer. Many theories have been proposed, ranging from unknown particles to tiny black holes or even changes to our understanding of gravity. However, none of these ideas have been proven correct.
One popular theory suggests that dark matter is made up of “weakly interacting massive particles” (or WIMPs). These particles are thought to be relatively heavy and could be responsible for the gravitational effects we observe. They are also believed to interact with regular matter, but only very rarely.
How Can We Detect Dark Matter?
If WIMPs exist, they should be passing through Earth all the time. Most of the time, they would go unnoticed, but occasionally, one might collide with the nucleus of an atom. This is what we are trying to detect in the LZ experiment.
Our experiment is located deep underground in an old goldmine in South Dakota, USA. Being so far below the surface helps to shield the experiment from background radiation that could interfere with our results. We use a large tank filled with seven tons of liquid xenon, a special gas cooled to –98°C. If a dark matter particle hits a xenon atom, it should create a tiny flash of light, which we can detect with our 494 light sensors.
However, dark matter isn’t the only thing that can cause these flashes. There is still some background radiation that we need to filter out to identify genuine dark matter signals. We do this by running detailed simulations of what we expect to see with and without dark matter.
What Have We Found So Far?
So far, our results haven’t shown any direct signs of dark matter. However, this helps us narrow down what dark matter could be. We found no evidence of particles with masses greater than 1.6 × 10–26 kilograms, about 10 times heavier than a proton.
Our findings are based on 280 days of observations. We plan to collect data for 1,000 days, which will give us an even better chance of finding these elusive particles.
Even if dark matter doesn’t show up in this experiment, we’re already planning a bigger and better detector for the future. The next-generation experiment, called XLZD, will be nearly 10 times larger and could help us finally uncover what dark matter is made of.
The search for dark matter is challenging, but each step brings us closer to solving one of the biggest mysteries in science.
Based on a story written by Theresa Fruth, The Conversation.
