A new detector in Canada has begun its search for the elusive dark matter, which scientists believe accounts for nearly 90% of all matter in the universe.
Scientists heard their first pops in an experiment that searches for signs of the invisible particles in the form of tiny bubbles.
They need further analysis to discern whether dark matter caused any of the COUPP-60 experiment's first bubbles at the SNOLAB underground science laboratory in Ontario, Canada.
Astrophysicists think dark matter accounts for about a quarter of the matter and energy in the universe. But no one has conclusively observed dark-matter particles.
"Our goal is to make the most sensitive detector to see signals of particles that we don't understand," said Hugh Lippincott, a postdoctoral scientist with the Department of Energy's Fermi National Accelerator Laboratory.
The COUPP-60 detector is a jar filled with 60 kilogrammes of purified water and CF3I - an ingredient found in fire extinguishers. The liquid in the detector is kept at a temperature and pressure slightly above the boiling point, but it requires an extra bit of energy to actually form a bubble.
When a passing particle enters the detector and disturbs an atom in the clear liquid, it provides that energy.
"This device has the potential to become the most sensitive dark matter detector in the world, for both modes of interaction expected from Weakly Interacting Massive Particles," said Juan Collar, associate professor in physics at the University of Chicago, who is leading the experiment.
Dark-matter particles, which scientists think rarely interact with other matter, should form individual bubbles in the COUPP-60 tank.
"The events are so rare, we're looking for a couple of events per year," Lippincott said.
Other, more common and interactive particles such as neutrons are more likely to leave a trail of multiple bubbles as they pass through.
Scientists will analyse the bubbles that form in their detector to test how well COUPP-60 is working and to determine whether they see signs of dark matter.
One of the advantages of the detector is that it can be filled with a different liquid, if scientists decide they would like to alter their techniques.