Hot iMac 50 degrees celsius!
The 21.5-inch, Late 2009, iMac has either a E7600 or E8600 Intel Core 2 Duo with a TCASE (Case Temperature is the maximum temperature allowed at the processor Integrated Heat Spreader (IHS).) temperature of 74.1°C and 72.4°C respectively.  So if the CPU is reading only 50°C, then it's not running hot at all.