Q:

What causes hot temperature extremes? 

Recently I looked into the hottest(and coldest, but in another question) natural places.  I find this to be a "cloud of searing gas that is surrounding a swarm of galaxies clustered together five billion light-years away in the constellation of Virgo".  This place has a temperature of 300 million degrees Celsius, which is super hot even compared to the temperature at our Sun's core.  A quick search why gives:

A group of galaxies collided violently with another swarm of galaxies at a speed of 2,500 miles per second. 

https://www.skymania.com/wp/hottest-spot-in-universe-found/

However, what mechanism exactly causes this temperature?  Friction?  Or something else?  Would stars there be fusing stuff from the outside?  

A:

Within that galaxy cluster, things become chaotic as these galaxies are flung around but kept in orbit by their strong gravity.  And as Steven Linton mentioned, 

the galaxy's organized motion is turned primarily into disorganized
  motion within the material that is stuck together, which is what we
  know as heat.  So the atoms of gas in these clouds collided and bounced
  off in all directions, where they hit other atoms, until the two
  clouds had formed one, with huge random internal motions (i.e. very
  hot).