My very basic understanding of GR leads me to think that if a substance has a high enough temperature, it can transform into a black hole without a mass required to create a black hole.
The equation that I figure can express this is: $$\frac{2G(m+(stm)/c^2)}{c^2}=\text{Schwarzschild radius}$$ Where $G$ is the gravitational constant, $m$ is mass, $s$ is specific heat, $t$ is temperature, and $c$ is the speed of light. "$stm$" is equal to heat in joules and when it is divided by $c^2$ it is equal to mass. The masses are then added together, and the equation becomes identical to the Schwarzschild radius equation.
I'm sure there are much more advanced principles than what I am familiar with at such high heats, but is the premise of my logic sound? I doubt that energy from heat can translate so easily into mass, but I don't see the error in writing it so. Also, would this mean that there is a "maximum temperature" since anything that surpasses it would create a singularity?