ScienceDaily (Apr. 4, 2009) — Astronomers are reporting the first clear detection of signatures long sought in the spectra of X-ray astronomical sources.

The research is being published in the journal Astronomy & Astrophysics.

These signatures, the so-called EXAFS standing for “Extended X-ray Absorption Fine Structure,” were observed with an X-ray spectroscopic technique that is common in materials sciences. Up to now, EXAFS studies of astronomical sources have been unsuccessful because of the weak X-ray signals received from celestial objects.

Using the Reflection Grating Spectrometer (RGS) onboard the XMM-Newton satellite, Dutch astronomers C.P. de Vries and E. Costantini, both of SRON/Utrecht Univ. Netherlands, have obtained high-quality X-ray spectra of Scorpius X-1, one of the brightest X-ray sources in the sky, located about 2800 parsecs from the Earth. For the first time, they have found clear evidence of an EXAFS signature coming from the dust seen toward a celestial source.

EXAFS is a powerful tool for studying the structure of grains in the interstellar medium (ISM). It is based on the phenomenon that X-ray photons can eject electrons from atoms inside solid particles, which in turn can be backscattered onto the emitting atom by atoms in their immediate neighborhood. This causes characteristic sinusoidal absorption features in the X-ray spectrum of a distant source that depend on the structure of the absorbing solid material.

Another, perhaps better known, technique of probing ISM dust, infrared spectroscopy, can also be used to study crystalline dust. However, EXAFS has a major advantage over infrared spectroscopy, in that it can probe the solid matter along the line-of-sight at the level of the atomic structure, even for irregular amorphous materials. Infrared spectroscopy, by comparison, provides information at the mineralogical level.

As a result, using EXAFS, astronomers can obtain a very detailed sampling of the composition and atomic structure of the dust along the line-of-sight. EXAFS gives a more detailed picture of the chemical composition and atomic structure of amorphous grains than is possible with infrared spectroscopy.

Story Source:

Adapted from materials provided by Astronomy & Astrophysics.

Journal Reference:

1. C.P. de Vries and E. Costantini. Physical properties of amorphous solid interstellar material from X-ray absorption spectroscopy of Scorpius X-1. Astronomy and Astrophysics, 2009; DOI: 10.1051/0004-6361/200811260

enlarge

Artist's impression of X-rays from a far-away source (top right) intercepted by an interstellar dust particle (yellow square), in which emittance and absorption of electrons between neighboring atoms causes a sinusoidal behavior in the observed X-ray spectrum. (lower left). Top right shows a drawing of the XMM satellite. (Credit: Image courtesy of Astronomy & Astrophysics)

Related Stories

First 'Garden Hose’ Jet Trail Nebula Discovered (Apr. 23, 2009) — Using the NASA Rossi X-ray Timing Explorer (RXTE) satellite, a team of astronomers have discovered an object predicted, but never seen before – a ‘jet trail’ nebula. The nebula ...  > read more

Organic Molecules Transport Strongest Spectral Signature Of Interplanetary Dust Particles (Jan. 23, 2005) — Carbon and silicate grains in interplanetary dust particles are helping scientists solve a 40-year-old astronomical ...  > read more

Meteorite Grains Divulge Earth's Cosmic Roots (June 16, 2009) — The interstellar stuff that became incorporated into the planets and life on Earth has younger cosmic roots than theories predict, according to ...  > read more

Interplanetary Dust Particles: Reproducing GEMS-Like Structure In The Laboratory (Feb. 16, 2006) — For the first time, a team of French scientists were able to reproduce the structure of the exotic GEMS (glass with embedded metal and sulphides) in the laboratory. The results of their experiments ...  > read more

Search ScienceDaily

Smart Sensors for Disasters