Main thread is the execution thread. As asked, it stays outside the event loop and will check for any events pertaining to the event loop.

If the even added to the event loop is synchronous and only needs some CPU operations, the main thread will take control directly and will execute the need.

If an asynchronous event is added to the event loop that is delegated to the worker threads available. Worker threads will perform the async operation(db/API/fs calls). Once the async part of the event is completed the event is again added to the event loop for the execution of the remaining synchronous part.

The worker threads are built over libUV and will spawn according to the main thread requirement. This reason makes Node.js more efficient while handling async calls and less preferred for CPU extensive operations.

Follow this for a more detailed explanation:
What function gets put into EventLoop in NodeJs and JS

In a Node.js application, when an HTTP request hits the server, the request is indeed received by the main thread before being passed to the event loop. The main thread in Node.js is the JavaScript main thread and it is responsible for executing user-written JavaScript code.

The event loop in Node.js is indeed the mechanism that allows non-blocking I/O operations to be performed. It works by offloading certain operations, such as file I/O or network requests, to the system kernel whenever possible, thus preventing the main thread from becoming blocked while waiting for I/O operations to complete.

To answer your question about where the main thread lives in relation to the event loop:
- The main thread exists outside of the event loop in Node.js.
- The event loop is a separate mechanism that coordinates I/O operations and callbacks alongside the main thread.

In Node.js, JavaScript is indeed single-threaded, meaning that all JavaScript code runs on this main thread. However, the event loop and other mechanisms in Node.js help facilitate non-blocking behavior and efficient handling of I/O operations.

As for a graphical representation of how Node.js works internally, there are various diagrams and illustrations available online that show the main components of Node.js, such as the main thread, event loop, callback queue, and system kernel interactions. You can refer to official Node.js documentation, online tutorials, or resources like technical blog posts and presentations for detailed graphical representations of Node.js internals.