Starship Asterisk*

What is the temperature of interstellar space? Is it determined by the proximity of the nearest star? The distance between stars is so vast that logically it would be indescribably cold, especially if there is no nearby surface to reflect light or heat. Just curious.

HERE is a theory about that.

But we should remember that space does not have a temperature. Only mass can have temperature.

brbear1 wrote:What is the temperature of interstellar space? Is it determined by the proximity of the nearest star? The distance between stars is so vast that logically it would be indescribably cold, especially if there is no nearby surface to reflect light or heat. Just curious.

Most likely, it is very hot. That is, the few particles you encounter will have high velocities. For instance, the temperature of space inside the Solar System reaches hundreds of thousands of degrees. Up where the ISS orbits, the temperature is thousands of degrees. But those numbers are all very misleading. Since there are so few particles, the efficiency of heat transfer is extremely low. The degree to which you will be heated up (or cooled down) by convective processes is vanishingly small. The dominant heat transfer process in a near vacuum is radiative. The temperature an object will reach in interstellar space is determined by its physical properties, the amount of radiation it absorbs from the distant stars, and what it radiates back out. You can pretty much figure that the equilibrium temperature for something in deep space, light years from any stars, is barely above the background temperature of the Universe, 2.7 K.

I recall reading that intergalactic gas gets up to hundreds of millions of degrees Kelvin.

Here's one site that says that, for example: http://library.thinkquest.org/C0126626/ ... %20gas.htm

-Noel

SmartAZ wrote:HERE is a theory about that.

But we should remember that space does not have a temperature. Only mass can have temperature.

That is according to the definition of temperature as the average kinetic energy of a mass. An alternate definition is the ability to transfer heat. In that regards, the temperature could be considered a little above 2.7 Kelvin, which Chris mentioned would be your equilibrium temperature in deep space. To say something is in thermal equilibrium with something else (eg, deep space) is equivalent to saying they have the same temperature.

Chris Peterson wrote:The dominant heat transfer process in a near vacuum is radiative.

Great post. That exact line, verbatim, actually popped into my head when I was reading the original question!