So we’re wondering if you could **hear sounds in a nebula**. We’ve figured out that sounds, which are waves of pressure, can be detected by humans if they are larger than 20 micro-pascals (μPa).

**So what is the pressure in a nebula?** The *Clear Science staff* looked it up, and found that a cold, dark nebula (like the Horsehead Nebula) will have *at most* at its core **100,000 particles per cubic centimeter**, which is a box about the size of the end of your pinkie finger. Also, **the temperature** will be about 10 kelvins, or -263 °C.

Using a little math, we can figure out about what pressure this would mean. **Don’t panic! **This is using the **ideal gas equation**, PV=nRT, and the level of difficulty is about the same as in a high school **Chemistry I class**.

- The quantity
**n/V** is a **concentration of particles**, so we plug in the 100,000 part. per cm^3 we looked up
- We use Avogadro’s number to convert the particles to
**moles**, because problems are easier to do in moles
**R** is the **gas constant**, which we look up: 8.314 J/mol/K
**T** is the **temp**, 10 kelvins
- And the
**last two terms we add are unit conversions**: 1: a joule is a newton meter, and 2: we convert to make sure all lengths are in meters and not centimeters

The answer we get is **14 pico pascals** or pPa. This is **much lower than 20 μPa**, so no, **there is not enough gas density in nebulae to support sound waves!** (At least not the kind of waves *we* call “sound.”)