what will happen when you kill the CTWR process on oracle database?

I did some simple experiment with CTWR. I killed the CTWR  process when the database running,but instance got terminated and shutdown.
alert log recorded the below error.

Instance Critical Process (pid: 38, ospid: 8984, CTWR) died unexpectedly
PMON (ospid: 3189): terminating the instance due to error 487