THE KELVIN SCALE

Of course, it is possible to freeze water and keep cooling it down or boil it all away into vapor and then keep heating it up. Temperatures can plunge far below 0°C and can rise far above 100°C. Are there limits to how low or how high the temperature can get?
Interestingly, there is an absolute limit to how low the temperature in degrees Celsius can become, but there is no limit on the upper end of the scale. We might take extraordinary efforts to cool a chunk of ice down to see how cold we can make it, but we can never chill it down to a temperature any lower than approximately 273 degrees Celsius below zero (-273°C).

This is known as absolute zero. An object at absolute zero can’t transfer energy to anything else because it possesses no energy to transfer. There is believed to be no such object in our universe, although some atoms in the vast reaches of intergalactic space come close.
Absolute zero is the basis for the Kelvin temperature scale (K). A temperature of -273.15°C is equal to 0 K. The size of the Kelvin degree is the same as the size of the Celsius degree, so 0°C = 273.15 K, and +   100°C = 373.15 K. Note that the degree symbol is not used with K.
On the high end, it is possible to keep heating matter up indefinitely. Temperatures in the cores of stars rise into the millions of degrees Kelvin. No matter what the actual temperature, the difference between the Kelvin temperature and the Celsius temperature is always 273.15 degrees.
Sometimes, Celsius and Kelvin figures can be considered equivalent. When you hear someone say that a particular star’s core has a temperature of 30 million K, it means the same thing as 30 million °C for the purposes of most discussions because±273.15 is a negligible difference value relative to 30 million.