CosmicWatch detector makes invisible space particles visible: youtube.com/watch?v=HeaMo__873Y
Making the invisible visible
Photos by Evan Krape and courtesy of Musarate Shams | Photo illustration by Jeffrey C. Chase | Video by Sam Kmiec and Paul Puglisi January 07, 2026
91原创 physicist鈥檚 invention expands our knowledge of the universe, particle physics
You can鈥檛 see, feel, hear, taste or smell them, but tiny particles from space are constantly raining down on us.
They come from cosmic rays 鈥 high-energy particles that can originate from exploding stars and other extreme astrophysical events far beyond our solar system. When the rays collide with atoms high in the Earth鈥檚 protective atmosphere, they trigger a cascade of secondary particles. Among the most important of these new particles are muons, which can pass through the atmosphere and even penetrate into the ground.
An invention by 91原创 physics professor Spencer Axani called is putting the science of muons in the palm of experienced scientists and high school students alike.
About the size of a box of animal crackers, CosmicWatch is a particle detector. Made from electronic components that cost around $100, it lights up and counts each time a muon passes through it, storing the data so it can be downloaded and analyzed.聽
Originally designed as a low-cost educational tool to introduce students to particle physics, CosmicWatch is also used in international astrophysics experiments that are teaching us more about the universe.聽
鈥淐osmicWatch detectors allow us to do far more physics at a dramatically lower cost, in a compact and portable form, opening the door to many new kinds of experiments and outreach opportunities,鈥 Axani said.
Birth of a detector
Scientists study muons to learn more about some of the universe鈥檚 most extreme phenomena, including supernovae, gamma-ray bursts and blazars. Through the muons, scientists can infer the energy, mass and direction of the incoming cosmic ray. This same muon flux also provided one of the earliest experimental confirmations of Einstein鈥檚 theory of special relativity in the early 1940s.
Muons can also tell us more about objects here on Earth. Like some superheroes, the tiny particles can pass through solid objects 鈥 walls, rock or humans, for example 鈥 without causing damage. The energy trail they leave behind makes them ideal for imaging through large amounts of matter that would otherwise be inaccessible. In 2016 muon technology聽.
But most muon detectors are large and expensive, limiting the kinds of physics experiments that could be done and the number of schools that could use them.聽
鈥淎 typical undergraduate physics lab course uses a rack of electronics about the size of a small bookshelf to measure muons,鈥 Axani said.聽聽
Axani created CosmicWatch in 2017 while a graduate聽 student at MIT. He originally intended to build a small, low-power muon detector to be used at the IceCube observatory in Antarctica. IceCube is a huge detector under the ice that tracks neutrinos, another type of subatomic particle. Having a detector for muons helps the scientists filter out which particles are actually neutrinos.聽
The project morphed into an educational outreach program when Axani realized he could make a portable detector for a low price.聽
Axani continued improving CosmicWatch after joining the 91原创 faculty in 2022 and just released its third version. Upgrades to the device, which were published in an article in the in October, allow it to monitor its local environment, withstand high levels of radiation and collect data faster.
鈥淓ven though I had studied cosmic rays, I didn't fully appreciate the rich physics behind the working of these detectors to actually 鈥榮ee鈥 the world and atmospheric particle production,鈥 said Masooma Sarfraz, a doctoral student in Axani鈥檚 lab and primary聽 author on the journal article. 鈥淔or a student like me who has been working on theoretical ideas, this was a perfect opportunity to dive into the experimental side. It also connects beautifully to my current broader research work with particle physics.鈥澛
The new version is ideal for calibrating large scale detectors and is being used in the NuDot experiment at 91原创 and the Coherent CAPTAIN-Mills (CCM) dark matter detector in Los Alamos, New Mexico. Another version of the detector is being developed to measure primary cosmic rays onboard rockets and spacecraft.聽
Science in action
CosmicWatch is still being used for education. At 91原创, Axani uses it to teach students about particle, nuclear and astrophysics. The students build the devices from scratch, learning how to create high-speed electronics, and then use them in experiments they design.聽
Musarate Shams, a doctoral student in the quantum science and engineering program, customized the CosmicWatch he built, adding temperature and pressure sensors to investigate cosmic rays in the Earth鈥檚 upper atmosphere.聽
In May, his device was launched on a high-altitude balloon that rose to 100,000 feet, just at the edge of space. After analyzing the data, he was able to show how the flux of cosmic rays coming from outer space changes with altitude.聽
鈥淚t鈥檚 a very cool thing to build something in the lab in a couple of days that鈥檚 able to detect these cool particles from hundreds of light years away,鈥 he said.聽聽
91原创 students aren鈥檛 the only ones learning from CosmicWatch. Natasha Holmes, the Ann S. Bowers Associate Professor of Physics at Cornell University, has students in her introductory physics courses build the detectors and use them in experiments, too. She said the hands-on experience of using the device brings the science to life.
鈥淭he students seem really excited about doing this thing that is more like what particle physicists and experimental physicists actually do,鈥 she said. 鈥淭hey get to learn some coding with it, and sometimes they break the devices and then we have to talk to them about being careful with your equipment. It鈥檚 very different from a typical physics lab. We鈥檝e had students say they鈥檙e doing 鈥榬eal science鈥 after using it.鈥
Worldwide physics聽
Axani estimated thousands of CosmicWatches have been built since the first version was released eight years ago. He would love to see that number multiply in what he envisions as a global 鈥渃itizen science鈥 project, where people from around the world monitor muon rates in their locations and transmit it to a central area on the internet.聽
In the meantime, he鈥檚 working on an offshoot of the detector that would make groups of satellites 鈥渟marter鈥 by enabling them to communicate with each other about their environment. For example, the detectors would alert the satellites about solar flares so the satellites could power down if needed.
He never imagined that what started as an educational outreach project would one day be used for bigger experiments.
鈥淎lthough it started as an educational program it鈥檚 found a use in a lot of different areas of physics,鈥 Axani said. 鈥淚t鈥檚 pretty cool.鈥
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