Neutrino study companion

Open the study companion, find answers in its FAQ, use the study timer, and chat with the optional AI about informatics, physics or astronomy.

Neutrino is a study companion available in two ways: click its glowing mascot (bottom-right by default) to open it in place, then choose Float inside the companion to open a separate window above your other windows. The floating window uses Chrome's Document Picture-in-Picture feature, so use a recent desktop version of Chrome and keep the Cherenkov tab open. The in-page companion works without Picture-in-Picture support.

The mascot

Neutrino's mascot is a small glowing lattice with a bright core and a ring around it. It turns slowly while you study and spins faster while it is thinking about an AI chat reply.

Move it: drag it anywhere on the page. Click it (or press Enter while it is focused) to open the companion. With the keyboard, focus the mascot and use the arrow keys to move it; hold Shift for bigger steps. The position is remembered on this device.
Hide it for now: hover or focus the mascot and use the small × button, or use Hide until I reload the page under the companion's Settings tab. A small button at the bottom-right brings it back.
Motion: if your system asks for reduced motion, the mascot stays still.

Ask: the FAQ and AI chat

The Ask tab has two modes, switched with the FAQ and AI chat buttons at the top. A notice under the buttons always says which one you are in, and the line under Neutrino's name in the header repeats it.

FAQ is where the companion starts every time. Its answers are written by the Cherenkov team and point to the right page of the site. It works without an account, and nothing you do there is sent to an AI. Pick a question from the list, search it, or narrow it by topic; the answer appears with links and a few follow-up questions. The text you type in the search box stays in your browser.
AI chat answers free-form study questions with replies generated by Google's Gemini. It needs an account, counts against the daily limit below, and can be wrong. See Study chat.

If AI chat is switched off in Settings, the Ask tab shows only the FAQ.

Settings

Open the companion and choose Settings, or go to Account → Study companion. Both places change the same settings.

Setting	What it does	Saved
Name	The name shown on the companion.	Your account (signed in)
Show the companion	Turn the mascot off on every page. Turn it back on here or under Account.	Your account (signed in)
Use AI chat	Turn off only the AI. The AI chat button disappears, the server refuses chat requests for your account, and the mascot, FAQ and timer carry on.	Your account if signed in, otherwise this device
Size	Small, medium or large.	Your account if signed in, otherwise this device
Rotation style	Automatic uses smooth 3D turning and switches to simple turning if your device struggles. 3D always uses 3D turning. Simple uses flat turning that needs less power.	Your account if signed in, otherwise this device

Resizing the panel

On screens at least 640 px wide the panel can be resized. It stays attached to the mascot, so the two edges that face away from the mascot (and the corner between them, marked with a small grip) are the ones you drag; the other two stay put. In the default bottom-right corner that means the top and left edges. The panel will not shrink below a usable minimum or leave the screen.

Keyboard: focus an edge (Tab) and use the arrow keys, which move that edge; hold Shift for bigger steps.
Reset: double-click an edge, or choose Reset panel size in Settings.
The size is remembered on this device. On narrow screens the panel is a bottom sheet with a fixed height.

Name and timer

The default name is Neutrino. While signed in, change it in the settings above. The name is saved to your Cherenkov account and appears the next time you open the companion.

The companion includes Cherenkov's study timer. It uses the same timer state as the regular timer page, so an active timer can be seen in either place. The timer state is kept in this browser's local storage. If you are signed in, completed focus sessions can be saved to your study log; breaks do not count as study time. See the study planner for the rest of the study tools.

Study chat

Study chat is the AI mode of the Ask tab. It is available only when you are signed in and have not switched it off. Neutrino uses Google's Gemini API to answer short questions about learning. It is meant for explanations, examples, checking your reasoning and hints. Avoid sending passwords, private information or anything you do not want sent to an AI service.

Cherenkov applies a limit of 10 chat requests per account per UTC day. A failed provider request and a retry each count as a request. The limit is shared by the normal Cherenkov Gemini configuration and a personal key. Messages are limited to 1,200 characters, only the latest six conversation messages are sent, and replies are limited to 256 generated tokens. These caps help keep the feature suitable for a small shared API allowance; Google's own model and project quotas still apply separately.

Google applies Gemini API limits by project and model. A 429 can mean a per-minute rate limit or a daily/project quota, and actual available capacity may vary. It does not by itself show that Gemini is down. A 503 indicates temporary service unavailability. Current limits depend on Google's project tier and the selected model; see Google's Gemini API rate limits and API error guide.

Errors and what to do

Message	What it means	What to do
Today's Cherenkov chat limit is used	This account has sent 10 requests during the current UTC day.	Wait until the next UTC day. A personal key does not extend this limit.
Cherenkov's Gemini project or model quota is exhausted	Google's API returned a quota or rate-limit response (`429`).	Try later. If the prompt offers it, you may choose to make one request with your own key.
Gemini is temporarily unavailable	Google's service returned a temporary service error, or the request timed out.	Try again later. The message does not claim a global outage.
Chat is not configured	Cherenkov's server is missing or cannot use its Gemini configuration.	Contact the Cherenkov team; changing your prompt will not fix server configuration.
Your personal key could not be used	Google rejected the submitted key or its project access.	Check the key and API access in Google AI Studio. The key is discarded after that request.

Using your own Gemini API key for one request

After a Gemini project quota, availability or server-configuration error, the companion may show an optional key form. Choosing it is entirely opt-in. Check the consent box, enter a Gemini API key and retry once. The key is sent from your browser to Cherenkov's server, then to Google to make that request. It is not stored in your Cherenkov account, database or browser storage, and the interface clears the field after the retry. The server does not log the key or Google's response body.

Cherenkov's per-account daily request limit still applies when you use your own key. Google applies the key's own project's model and quota limits, and Google's terms govern that request. Only enter a key you control, and do not use the form if you are not comfortable sending it to both services.