Scientists this week heard their first pops in an experiment that searches for signs of dark matter in the form of tiny bubbles. Dark-matter particles, which scientists think rarely interact with other matter, should form individual bubbles in the Fermi COUPP-60 tank.
The COUPP-60 detector is a jar filled with 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 itrequires 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.
Other, more common and interactive particles such as neutrons are more likely to leave a trail of multiple bubbles as they pass through.
Over the next few months, scientists will analyze 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.
The COUPP-60 detector is the latest addition to a suite of dark-matter experiments running in the SNOLAB underground science laboratory, located in Ontario, Canada. Scientists run dark-matter experiments underground to shield them from a distracting background of other particles that constantly shower Earth from space. Dark-matter particles can move through the mile and a half of rock under which the laboratory is buried, whereas most other particles cannot.
Scientists further shield the COUPP-60 detector from neutrons and other particles by submersing it in 7,000 gallons of water.
Scientists first proposed the existence of dark matter in the 1930s, when they discovered that visible matter could not account for the rotational velocities of galaxies. Other evidence, such as gravitational lensing that distorts our view of faraway stars and our inability to explain how other galaxies hold together if not for the mass of dark matter, have improved scientists’ case. 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.
The COUPP experiment includes scientists, technicians and students from the University of Chicago, Indiana University South Bend, Northwestern University, University of Valencia, Virginia Tech, Fermi National Accelerator Laboratory, Pacific Northwest National Laboratory and SNOLAB.
Clues from the Chandra X-Ray Observatory (image at the top of the page) have enabled scientists to constrain the size of dark matter particles in galaxy clusters. Dark matter is the invisible and unknown material that constitutes about 80% of the matter in the Universe.
The Daily Galaxy via FermiLab
Image Credit: NASA/SAO/CXC