Located in the frigid desert that is the South Pole, the IceCube Neutrino Observatory isn’t your typical telescope. It doesn’t have an observatory dome or satellite dish. In fact, if you were standing at the South Pole looking at IceCube, you would see nothing but a small building in a vast, barren, snowy landscape.
That’s because the IceCube detector is underground. It comprises an array of 5,160 optical sensors that are frozen beneath a cubic kilometer of ice a mile beneath the surface. These sensors pick up signals left behind by mysterious particles called neutrinos.
Now, thanks to a new augmented reality (AR) app, anyone in the world can see what’s happening under the ice at the South Pole. And when a neutrino candidate sails through the detector, users will find out in real time!
Introducing IceCubeAR, aka IceBear.
Neutrinos are fundamental particles that travel through the cosmos. They come from myriad sources on Earth and in our solar system—but many are from outside our galaxy, known as astrophysical neutrinos, and those are the ones IceCube is interested in. Through IceCubeAR, users can receive neutrino alerts in real time, visualize the neutrino interaction in the detector, and see the estimated source direction projected onto a sky map.
The project was headed by IceCube collaborator Dr. Lu Lu and co-developed by Colin Baus, Vsevolod Yugov, and Thomas Hauth. It started as an app for the Microsoft HoloLens (see a demo here), but the team recently adapted it into an AR app for smartphones.
What does IceCubeAR show?
The IceCubeAR app shows visual representations of “neutrino events”: the patterns of sensors that light up in response to a passing charged particle.
IceCube doesn’t actually observe neutrinos directly. Instead, it detects light from charged particles produced when a neutrino crashes into an atomic nucleus. These charged particles travel faster than light in ice, creating “Cherenkov radiation”—like a sonic boom, but with light.
As the Cherenkov cone flies through the detector, it triggers IceCube’s in-ice sensors, called digital optical modules (DOMs). Each DOM houses an extremely sensitive photomultiplier tube along with minicomputers that relay data to the IceCube Laboratory at the surface.
These data are analyzed automatically at the South Pole, and if the event has a good chance of being a high-energy astrophysical neutrino, an alert is generated and shared with the entire astronomical community. This whole process happens in less than one minute. IceCubeAR users will receive these alerts at the same time. (However, not all of these candidate events turn out to be astrophysical neutrinos.)
Neutrino candidate events are sent out as either “gold” or “bronze” alerts. Gold denotes that the event has roughly a 50 percent probability of being astrophysical in origin; bronze means it has about a 30 percent probability.
The event’s pattern and colors indicate the particle’s direction and energy: The colored spheres represent DOMs that have detected light, and color indicates the time that the DOM was hit (red is earlier, green/blue is later). The size of the sphere scales with the amount of light recorded. The arrow indicates the estimated direction that the particle traveled through the detector. By tracing this trajectory backward, IceCube scientists hope to find the source that produced the original neutrino.
For now, IceCubeAR only shows one type of event, known as “tracks.” IceCube also detects “cascade” events, though these are not yet part of the app.
Please also note that this app is intended to be a fun tool for outreach; users cannot make scientific discoveries with IceCubeAR. If you have scientific questions on IceCube alerts, you may contact IceCube’s realtime oversight committee at email@example.com.
How to use the app
You can watch a demo of the app here.
1. Please allow camera access for AR. If you wish to receive notifications when alerts come, please give permission. Note that the initial download of the event list could take more than one minute, so please be patient on your first try!
2. Move device slowly to find a flat surface. When you see a triangular grid on the surface, tap to place the IceCube array. It works best in a well-lit area! (See image to the right.)
3. Pinch with two fingers or use the scroll bar on the left side to scale the detector.
4. Tap gray bar of text on bottom of the screen. This is the event list, showing neutrino candidate events and the dates they were detected. Not all of these are neutrinos—some were later found to be cosmic rays (a different kind of particle that IceCube isn’t as interested in). IceCube’s most famous events are on one end. Select an event.
5. You can play with the various toggles in the gray menu on the bottom of the screen, but you don’t need to touch these to enjoy the app. Some of these adjustments are more technical.
a. The color gradient slider allows you to adjust the way the colors change in time. The event looks best if the first notch (red) is aligned with the start of the event in time and the last notch (blue) is aligned with the end of the event. (Each event starts with a default color map that is close to this.)
b. The middle slider, labeled dt, adjusts how the size of the colored DOMs change over time. If this slider is all the way to the right, the colored spheres stay the same size throughout the event. If the slider is all the way to the left, the spheres will appear to lose their charge as time passes.
c. The third bar is the timeline; drag the triangle to move the event forward or backward in time.
6. Tap the small carrot to collapse the gray menu.
7. Tap the triangle Play button to watch the event appear in front of you! Turn the sound on to hear sonification of the event! Each string has an assigned instrument based on its radius from the center; tones are determined by the height of the triggered DOM.
8. Tapping “Reset” in the upper right will allow you to reposition the IceCube detector.
9. Check the box on the top of the screen next to “Tokyo Tower” to toggle a model Tokyo Tower next to the detector. This is to demonstrate the relative scale of IceCube. More monuments and buildings are coming soon.
There is still lots of room for improvement, and the development team is open to suggestions. You may send them an email at firstname.lastname@example.org.
If you enjoy playing with ICEcuBEAR, take a screenshot or record a video of you or your friends interacting with the neutrino events and share it with us on social media! Use the hashtag #IceCubeAR and tag us on Twitter (@uw_icecube), Facebook (@icecube.neutrino), or Instagram (@icecube_neutrino).