Does the pool contract is automatically liquidate the borrower debt?

In liquidation process. if an borrower account is under Collateralize, then the borrower health factor bellow 1. that time there is no liquidator is try to repays the borrowers debt then what will happen? in the pool contract?

1. The pool contract is automatically liquidate the borrower debt? or
2. It will wait until the liquidator came to repays the debt of borrower?