What is the $ORACLE_HOME/dbs/hc_$ORACLE_SID.dat file?

In every $ORACLE_HOME/dbs folder you will find a file named hc_$ORACLE_SID.dat.

What is it, and is it essential for your instance?

Oracle Support states:

The $ORACLE_HOME/dbs/hc_.dat is created for the instance health check monitoring. It contains information used to monitor the instance health and to determine why it went down if the instance isn't up.

The file can be deleted while the instance is up, it won't cause any harm to your instance.

In earlier versions of the Oracle database software a bug existed that would trigger an ORA-7445 if the file was deleted while the database was up, but this was fixed as early as in version 11.2.

The file is created at every instance startup.

Source: What Is The $ORACLE_HOME/dbs/hc_.dat File? (Doc ID 390474.1) from Oracle Support