HACing out a dusty light source.

HACing out a dusty light source

Studying the spectra of a tough compound that coats some electrodes and the fuel pellets used in fusion experiments has helped solve a long-standing astronomical mystery -- the emission of red light from interstellar dust clouds.

The curious interstellar emissions appear to arise from a solid form of a diamond-like compound known as hydrogenated amorphous carbon (HAC), report David A. Williams of the University of Manchester in England and his colleagues at York University in Ontario. Their laboratory experiments show that HAC absorbs short-wavelength light and reradiates it at red and infrared wavelengths closely matching the spectra emitted by interstellar dust.

The researchers point out that differing properties of the two known forms of HAC may explain observed variations in absorption and emission properties of interstellar dust clouds. Polymeric HAC, for example, contains an abundance of hydrogen and strongly absorbs ultraviolet. Graphitic HAC contains less hydrogen and absorbs visible light. Such telltale differences in the spectra of each HAC may allow scientists to calculate the hydrogen in a given region of interstellar dust, the investigators say. They will detail their work in upcoming publications of the Royal Astronomical Society.