Dust in Galaxies: Clumps Instead of Haze express
Light from a distant galaxy reaches us through its own dust. This dust is not a smooth haze but ragged clouds, like wisps of cotton. Old models treated it as a uniform mist, and then the galaxy didn't add up energetically: too much light disappeared in the ultraviolet and too little came back in the infrared.
Astronomers did what a cook does when they dice a potato instead of tossing it in whole. They replaced each dense dust cloud with a virtual 'pseudo-grain' having the same properties — how it absorbs light, how it scatters, how it glows when warm. These pseudo-grains were added to the standard dust model. The absorption curve became flatter: the dust stopped gobbling up blue light so greedily.
They applied the model to seven galaxies with different inclinations. It turned out that clumpy dust lets more light through than previously thought: the maximum optical depth in the blue filter dropped by a factor of 1.3–2.8. Two galaxies remained opaque at their centers, two were moderately transparent, and three were clear.
Clumps change the picture: you need less dust to explain the same absorption. So estimates of dust mass in galaxies may be too high. And light from distant stars reaches us more easily than we used to think.
In the galaxy NGC 891, dust is gathered into clouds that resemble giant 'filaments'—visible in images as dark streaks across the disk.
In Charles Pellegrino's novel 'Dust', interstellar dust becomes a threat to a starship — the clumpy structure of the dust makes collisions more dangerous.