There is a phrase in a Science Daily article which appears to be wrong:

The Milky Way has a very high content of carbonaceous dust, which has been shown to be very rare in other galaxies.

Is there a theory that explains these observations?

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    $\begingroup$ The abstract of the linked article seems to say that this type of dust is rare at high red shifts, which is not the same thing add being rare in other galaxies $\endgroup$ – Steve Linton Jul 7 '18 at 15:51
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    $\begingroup$ @com.prehensible: what part of the statement do you believe to be wrong: the high level of atomic carbon in the Milky Way, or its rarity in other galaxies? Also, these are observations rather than theory. Perhaps you could amend your last sentence to ask "Is there a theory that explains these observations?" But +1 for a fascinating question, I look forward to seeing an answer! $\endgroup$ – Chappo Jul 7 '18 at 23:50
  • $\begingroup$ @SteveLinton the full article says "Beyond the local Universe, the 2175 ̊A extinction feature [indicating neutral atomic or molecular carbon] becomes very uncommon". The "local Universe" in this context means the MW and two Magellanic Clouds. But the feature does seem to be observed at z>1. So, why don't galaxies at lower redshift show it? $\endgroup$ – Chappo Jul 8 '18 at 0:06
  • $\begingroup$ Good idea to check the article reference, I had searched google and had found an abstract from 2010 which stated that carbon in galaxies didn't vary a lot, so I thought that ScienceDaily was wrong. Any information is good because previously it was a mystery if it was graphite / naphthalene / polysaccharides. $\endgroup$ – com.prehensible Jul 8 '18 at 7:38
  • $\begingroup$ I'm assuming you mean a theory for why the emission bump doesn't appear in all observations of other galaxies, and not why it's present at all, right? The latter seems to be settled in favor of a graphite lattice; at least, that's what's been theorized for ~50 years. $\endgroup$ – HDE 226868 Jul 8 '18 at 20:18

From the introduction of the source paper, we can see that what is described is a particular bump in the extinction curve of the galaxy centered at 2175 Ångström (a unit of length used for wavelength). The strength of this bump is large compared to the Large Magellanic Cloud, and is rarer toward the Small Magellanic Cloud.

As mentioned in the comments, the main candidates for the origin of the feature are non-graphitic carbon or polycyclic aromatic hydrocarbons (PAHs). The absence in other environments is attributed to low metallicities or different radiative environments.

Basically, this is a case where we lose information in science reporting. "Very high content of carbonaceous dust" was a translation of a specific strength at a specific wavelength, and "other galaxies" was a translation of surrounding galaxies.



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