Algorithmic Money Operations (or AMOs) are an investment strategy that utilizes the collateral that is locked up in the unused pools to earn interest that will be paid to all stakers and ARTHX holders.
An AMO can be thought of as a strategy that utilizes unused funds from the ARTH collateral pools and invests them into protocols like Compound Finance or AAVE to earn extra yield.
An AMO gets its funds from the ARTH collateral pools. The collateral pools contain collateral that is deposited by users which is used to back ARTH. An AMO is given special permission to a collateral pool to borrow funds from it.
Hence funds for an AMO to invest are borrowed from the ARTH collateral pools.
The returns are given back to ARTHX holders through the ARTHX staking pool.