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The planet is cold and black deep underwater, thousands of miles off the Canadian coast of British Columbia. A group of underwater buoys that are firmly moored to the ocean floor bob upward from the sand below. Each line has huge glass spheres that are tethered at regular intervals and are equipped with sensitive light-detecting equipment. This deep-sea equipment wasn’t built by biologists or oceanographers but by scientists. They are astronomers and physicists. They are attempting to trap neutrinos, which are cunning, shape-shifting, practically massless particles that have the potential to alter our understanding of the cosmos, here, 2 kilometers beneath the icy Pacific oceans.
The majority of physicists’ work is spent observing mid- to low-energy neutrinos, which are frequently produced by particle decays. A high-energy cosmic neutrino, however, is occasionally found, which is a different form of neutrino. Since these super-powered particles have so high energy, scientists can assume that extreme things outside of our galaxy must have accelerated them. Juan Pablo Yanez Garza, a physicist and assistant professor at the University of Alberta, claims that “these energies are pretty hard to conceive.” You would want a “accelerator” the size of a whole galaxy to excite neutrinos to this degree, which is evident when you take into account how we accelerate particles in modern laboratories, such as the Large Hadron Collider, and factor in the average magnetic fields in the universe.
Scientists have just recently started to identify some of the extragalactic origins of these particles using enormous, specialized detectors. Finding the source of high-energy neutrinos can help address long-standing puzzles about the enormous cosmic accelerators that produce them, put an end to open-ended debates over cosmic rays, and even offer indications about the beginnings of dark matter. The Pacific Ocean Neutrino Experiment, or P-ONE, is a proposed experiment that scientists hope would enable them to understand the origins of cosmic neutrinos. The instruments in the Pacific Ocean are some of the initial stages toward this experiment.
Most of the universe is veiled from photon-based telescopes because of the size of the universe and the prevalence of view-obscuring dust clouds. Instead, to understand more about these dark regions, which contain some of the most powerful things in the universe, astronomers search for messenger particles, such as neutrinos. The best cosmic messengers are neutrinos. Due to their few interactions with other particles and chargelessness, they can travel quickly through space without being hampered by dust or magnetic fields.
However, because of their introversion, they might be challenging to capture once they arrive on Earth. In an effort to improve the chances, scientists have created goliath detectors. The likelihood of catching a high-energy cosmic neutrino is quite remote. Only a few hundred have been detected by the IceCube detector in its twelve years of operation, despite being one of the most important cosmic neutrino observatories and having a detection volume of one cubic kilometer. According to Lisa Schumacher, a research scientist at the Technical University of Munich who works on both IceCube and P-ONE, “We still do not know what most of the cosmic high-energy neutrino sources are, even with more than 10 years of data from IceCube.”
However, we are aware of some of them. A blazar located 3.7 billion light years away was identified as the origin of high-energy neutrinos in 2018 by the IceCube observatory. Powered by a black hole that can propel particles in massive jets at nearly the speed of light, a blazar is the galaxy’s core. After that, in 2022, IceCube revealed a second source in a nearby, active galaxy that is only 47 million light years away, where researchers believe neutrinos and other particles are accelerated around a massive black hole. Statistical analyses reveal that active galaxies cannot entirely account for all high-energy astrophysical neutrinos, despite the fact that they are now a source that has been confirmed. Elisa Resconi, a professor at the Technical University of Munich and an IceCube expert, claims that “the issue is that we need more data. “Statistics is what is currently constraining us,”
Scientists like Resconi have been envisioning novel neutrino observatories in order to amass more data. Resconi led the charge to get the new massive P-ONE experiment up and running. The experiment’s purpose is to supplement IceCube by constructing hundreds of neutrino detectors along numerous 1-kilometer-long lines. P-position ONE’s in the northeast Pacific makes it a potential neutrino detector for sources outside the reach of IceCube. “The aim is to create a telescope that would be similar to IceCube but with advantages given advances in technology over the last decade,” Resconi says. Our ultimate goal is to collaborate with other detectors and combine our data sets.
Like IceCube, P-ONE will detect neutrinos by searching for the small light streaks created when neutrinos collide with other particles in a media like water or ice. Subterranean placement of neutrino detectors is common practice since it helps to shield the instruments from other atmospheric particles that can masquerade as these tiny streaks. The Sudbury Neutrino Observatory in Canada and the Super-Kamiokande in Japan are two examples of neutrino detectors constructed in or near active mines. Some, like Russia’s Baikal Deep Underwater Neutrino Telescope and the planned future Cubic Kilometre Neutrino Telescope off the coast of Italy and France, are constructed at great depths below the surface of the ocean. The goal of the researchers at P-ONE is to expand the size and scope of the aquatic fleet.
P-ONE has an advantage over IceCube, which is buried two thousand meters beneath the surface of the ice. Polar ice may be very see-through, but its crystal structure distorts a light beam so that it can’t move in a straight path. This diffusion hinders IceCube’s ability to pinpoint cosmic neutrino factories by using the angle and direction of the streaks as a proxy for their point of origin in the sky. While P-detectors ONE’s won’t be able to measure as much light as IceCube, Schumacher claims they will be able to better recreate the source of the light they do measure.
Scientists have proposed constructing P-ONE atop Ocean Networks Canada’s oceanographic observatory, the world’s largest permanent oceanographic infrastructure. If they are successful, P-ONE scientists will be able to use the network of hundreds of kilometers of optical cables and substations already established on the ocean floor, saving time and money on the experiment. In exchange, P-ONE may also provide new opportunities in oceanography and biology. Extra detectors, like as hydrophones or oxygen sensors, might be connected to the P-ONE lines to conduct acoustic tomography, which utilizes low-frequency transmissions to assess ocean currents and temperature across wide regions.
And because P-detectors ONE’s are sensitive to light, they might also be utilized to examine long-term changes in bioluminescence activity in the deep. In 2018, the project scientists deployed STRAW-a, a cluster of instruments designed to evaluate the site’s appropriateness for the P-ONE experiment. Along with STRAW-b, whose tests concluded in 2021, the pathfinder mission demonstrated that the location’s pristine seas would be an excellent canvas for neutrino detection. Now, scientists are planning for the next phase, which will involve the installation of a prototype sensor in the spring of 2024.
At least three lines, each with 20 detectors, will be deployed on the ocean floor during the prototype phase. This should enable scientists to capture approximately 30 atmospheric neutrinos, sufficient for calibration and proof of concept. If all goes according to plan, P-ONE will consist of seventy 1,000-meter-long lines stretched across one square kilometer of ocean. And if the project’s popularity grows, the experiment is highly scalable. With P-ONE, IceCube, and other upcoming detectors, neutrino astronomy can be conducted properly, according to Resconi. “We’ll be able to target a large number of objects and do population studies to determine which things emit the most neutrinos.”