What is the density of the Carina Nebula?

[ozipin]

In a James Webb photo thread, someone posted that the Carina Nebula has a density of a few atoms per cubic meter. This seems off to me, as this is close to the average density of the intergalactic medium of one atom per cubic meter, which is much less than the interstellar medium average density of one atom per cubic centimeter, which is much less than the average density of a planetary nebular (100-10,000 atoms per cubic centimeter). But I can't find any information on the web to help me understand this better.

 

[PeterDonis]

Moderator's note: Thread moved to astronomy forum.

 

[Ibix]

I take it that it was you who asked the same question on reddit? If not, a poster there cited https://academic.oup.com/mnras/article/456/3/2406/1089538?login=false, which gives column densities that are about consistent with the NASA figures.

 

[phyzguy]

I believe the Carina nebula is what is called a Giant Molecular Cloud (GMC). The Wikipedia article says the following: "Whereas the average density in the solar vicinity is one particle per cubic centimetre, the average density of a GMC is a hundred to a thousand times as great." The value of one atom/cubic meter is about the average mass density of the universe as a whole, so is much too low for even the vicinity of the sun, let alone a dense nebula like Carina.

For a more scholarly reference, this paper has the following quote, "By terrestrial standards, the interstellar matter is exceedingly tenuous: in the vicinity of the Sun, its density varies from ∼ 1.5 × 10−26 g cm−3 in the hot medium to ∼ 2 × 10−20 − 2 × 10−18 g cm−3 in the densest molecular regions, with an average of about 2.7 × 10−24 g cm−3 (see next subsections). This mass density, which corresponds to approximately one hydrogen atom per cubic centimeter, is over twenty orders of magnitude smaller than in the Earth’s lower atmosphere."

 

[Bandersnatch]

which gives column densities

Translating column density to density requires some specialist knowledge, though. I'm not sure it helps the OP by itself.

 

[Ibix]

Translating column density to density requires some specialist knowledge, though. I'm not sure it helps the OP by itself.

Sure - the reddit poster translated the column densities into a density range on an assumption that the nebula was about 15ly deep from our perspective.