A new Guinness World Record has been recognized for hottest man-made temperature at 4 trillion degrees Celsius, which, if you can imagine it, is 250,000 times hotter than the center of our own sun.
The Brookhaven National Laboratory with its Relativistic Heavy Ion Collider (RHIC), a "2.4-mile underground atomic 'racetrack,'" created the insanely hot "liquid-like quark-gluon plasma" by smashing together gold ions.
“There are many cool things about this ultra-hot matter,” physicist Steven Vigdor, who leads Brookhaven’s nuclear and particle physics program, said in the announcement on the Brookhaven website. “We expected to reach these temperatures – that is, after all, why RHIC was built – but we did not at all anticipate the nearly perfect liquid behavior.”
Brookhaven speculates that it might not old the record for long. ALICE at the large hadron collider at CERN in Geneva is larger and according to a CERN physicist has an energy density higher than RHIC by a factor of three. Still ALICE didn't publish an official temperature for Guinness to approve so RHIC's reading stands as hottest for now.
Watch this video from a couple years ago explaining what RHIC researches: