cosmic dust

History

The existence of cosmic dust was hypothesized as early as the 19th century, but serious study began with the development of astrophotography in the 20th century, when dark spots blocking stars were noticed on photographs.

How it works

Just as dust in the atmosphere gives sunsets red hues, cosmic dust makes the light from distant stars redder. Small particles scatter blue light more strongly than red, so the red part of the spectrum predominantly reaches the observer — this effect is called interstellar reddening.

History

The existence of cosmic dust was hypothesized as early as the 19th century, but serious study began with the development of astrophotography in the 20th century, when dark spots blocking stars were noticed on photographs.

How it works

Just as dust in the atmosphere gives sunsets red hues, cosmic dust makes the light from distant stars redder. Small particles scatter blue light more strongly than red, so the red part of the spectrum predominantly reaches the observer — this effect is called interstellar reddening.

History

The existence of dark regions in the Milky Way has been known since antiquity, but their nature remained a mystery for a long time. In the 18th century, William Herschel suggested they were 'holes in the heavens'. Only in the early 20th century did Edward Barnard and other astronomers prove that they are clouds of light-absorbing matter. A decisive contribution was made by Robert Trumpler in 1930, who showed that distant star clusters appear redder and dimmer due to interstellar absorption, revealing the existence of scattering dust particles. Later, spectroscopic and infrared observations allowed detailed study of the composition and distribution of dust.

How it works

Cosmic dust interacts with electromagnetic radiation through absorption (photons turn into thermal energy) and scattering (photons change direction). Mie theory is used to describe scattering on spherical particles, and the Rayleigh approximation for very small particles. Dust also emits in the infrared range according to Planck's radiation law, modified for emissivity depending on composition. Chemical reactions on the surface of dust grains, including the formation of molecular hydrogen, are catalyzed by low temperatures and a large surface area. Elongated particles, aligned by the galactic magnetic field, cause partial linear polarization of transmitted light (polarimetry).

Open problems & fun facts

The exact chemical composition and nuclear structures of dust grains, especially the carbon component, remain a subject of debate.; The role of dust in the formation of complex organic molecules, including prebiotic ones, is not fully understood.; Dust introduces uncertainty into measurements of cosmological redshift and dark energy parameters.

💡 Analysis of meteorites shows that cosmic dust can preserve presolar grains — microscopic crystals of silicon carbide and diamond, formed in the atmospheres of ancient stars and surviving the formation of the Solar System.