GLOBLA_STATS vs USER_STATS

 Hi

I have created a table and loaded the data into the table using import utility, after two days I have checked the dba_tables for the specific user,  the table having last_analyzed date. but I have not run any analyze command or dbms_stats process is also false.

SQL> select JOB_NAME,state,enabled from dba_scheduler_jobs WHERE job_name LIKE 'GATHER%';

JOB_NAME                       STATE           ENABL
------------------------------ --------------- -----
GATHER_STATS_JOB               DISABLED        FALSE

can any one of you please tell me, how the last_anlyzed date got updated, and what is the different between global_stat and user_stat. Is there any background job collects the stats automatically.