I am 100% sure you're issue is the hybrid graphics and I have finally managed to tame this issue in most overheating laptops out there. Here is the ugly but workable hack:
yes there is an ugly hack, which needs to be in place so that it shuts down your discrete graphics card on boot and will disable it on ubuntu. Which I think should be fine as it will totally chill your system
Step1. goto terminal (alt+ctrl+t) and type:
sudo gedit /etc/rc.local
Step2. add the following lines before exit 0:
echo IGD > /sys/kernel/debug/vgaswitcheroo/switch
echo OFF > /sys/kernel/debug/vgaswitcheroo/switch
So your rc.local would look something like this:
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
echo IGD > /sys/kernel/debug/vgaswitcheroo/switch
echo OFF > /sys/kernel/debug/vgaswitcheroo/switch
exit 0
Step3: Save and exit gedit, then type:
sudo reboot
Enter your password when required.
Basically what you did was, you switched to Integrated (IGD) graphics. then switched off the other one.