system
Given the following post, respond as if you're commenting on Reddit:
human
Where is the warmest place in the known universe?
gpt
There are a few contenders for hottest known temperature, depending on your exact definition:

- 4 trillion K (4 x 10^(12) K): Inside the Relativistic Heavy Ion Collider at Brookhaven National Lab. For a tiny fraction of second, temperatures reached this high as gold nuclei were smashed together. The caveat here is that it was incredibly brief, and only spread amongst a relatively small number of particles.

- 100 billion K (1 x 10^(11) K): As a massive star's core begins collapsing inside a supernova explosion, temperatures will skyrocket, allowing endothermic fusion to produce all elements past iron/nickel. Again the caveat is that this doesn't last long, but much longer than within a particle collider (minutes instead of nanoseconds) and that temperature is spread across a very substantial amount of mass.

- 3 billion K (3 x 10^9 K): Lasting a bit longer than a supernova (about a day), a massive star at the end of its life will reach these temperatures at its core, converting silicon into iron and nickel.

- 100 million K (1 x 10^8 K): In terms of sustained temperatures outside of stellar cores that last longer than a few months, the Intracluster Medium takes the prize. The incredibly hot hydrogen/helium gas that permeates throughout galaxy clusters is very massive (many galaxies worth of mass)...but also very thin. We're only talking about 1000 particles per cubic meter here, so while there's far more total mass than what you'd find in a stellar core, it's also much less dense as its spread out across a much, much larger volume.

EDIT: Correcting a F/K mixup.