The lowest temperature at which fire can burn depends on the fuel and the conditions under which it is burning. In general, fire is sustained by the combustion of a fuel source in the presence of oxygen and heat. The fuel must reach its ignition temperature, which is the minimum temperature required to initiate and sustain combustion.
Different fuels have different ignition temperatures. For example, wood typically ignites at around 300 degrees Celsius (572 degrees Fahrenheit), while gasoline has an ignition temperature of approximately -40 degrees Celsius (-40 degrees Fahrenheit).
However, it's important to note that fire cannot burn at temperatures below absolute zero, which is the lowest temperature possible in the known laws of physics. Absolute zero is defined as 0 Kelvin, or approximately -273.15 degrees Celsius (-459.67 degrees Fahrenheit). At this temperature, molecular motion ceases, and there is no heat energy available for combustion to occur.
So, while the ignition temperatures of various fuels may differ, there is a limit to how low the temperature can be for fire to sustain itself, and that limit is above absolute zero.