How dense is space dust?


Like in the attached threads ( would it be like fog if we were to go through it or would we not even notice it if we were in it? Follow up, if that’s the case how is all the dust so contracted in one area to look so massive?

In: Other

Nubulaes like the one from the photo have densities of [up to tens of thousands of atoms per cm^3](, which is about a *hundred trillions* less than air.

You wouldn’t feel or see anything if you where close to it.

These clouds are huge, they can be several light years in size. Even if they are very thin, their gravity (plus all the stars inside) pulls them together over billions of years.

The density depends on where in space you are exactly, but never dense enough to be visible. Most “empty space” has, on average, a handful of particles per cubic centimeter (for reference, air at sea level pressure has about 10^19 molecules per cubic centimeter). Even the most dense nebulae only have a few thousand particles per cubic centimeter.

It’s important to know that while we call it dust, it’s not dust like we know here on Earth. Space dust is not individually visible particles. When we talk about space dust, we’re talking about particles that are anywhere from few micrometers (millionths of a meter) to just a few molecules in size.

1 Atmosphere (== 760 torr) has 2.5×10^19 molecules per cm^3

Super hard lab vacuum (the best achievable practically) = 10^-9 torr. That’s 3.3×10^7 molecules per cm^3 .

Ordinary space is about 1 molecule per cm^3 , but visible structures like shown in the picture are more like 10^4 molecules per cm^3 . They are better than any vacuum we can make on Earth, but much more stuff than normal space.