Herschel detected argon signatures in the Crab Nebula

Dec 14, 2013 08:34 GMT  ·  By
Emission spectra collected by Herschel reveal the presence of argon-based molecule in the Crab Nebula
   Emission spectra collected by Herschel reveal the presence of argon-based molecule in the Crab Nebula

A team of astronomers from the University College London (UCL), led by expert Michael Barlow, was recently able to use observations from the European Space Agency's (ESA) Herschel Space Observatory to determine that gaseous filaments in the famous Crab Nebula contain argon molecules. 

This study marks the first time that the signatures of noble gas-based molecules are detected in space. Scientists hypothesized that this class of chemicals can exist in nebulae and other cosmic formations, but evidences to support this idea have thus far been lacking.

The discovery was made as UCL astronomers were investigating wispy gaseous filaments in one of the most famous nebulae out there. Data from Herschel revealed the presence of argon-based molecules in the supernova remnants, something that researchers were not looking for.

Supernova explosions – the most energetic in the Universe – are known to be capable of producing some types of noble gases, including argon, but the fact that the chemicals can endure in remnants comes as a surprise for astronomers.

Most noble gases, including helium, neon, argon, krypton, xenon and radon are inert. Argon's very name comes from the Greek word for idle, referring to its unwillingness to interact with other elements.

In a paper published in the latest issue of the top journal Science, researchers detail how they were able to discover a molecular ion called argon hydride (ArH+) in emissions spectra collected by Herschel, which was the world's most complex and advanced telescope.

“At first, the discovery seemed bizarre. With hot gas still expanding at high speeds after the explosion, a supernova remnant is a harsh, hostile environment, and one of the places where we least expected to find a noble-gas based molecule,” Barlow explains.

He adds that argon hydride is made up of argon ions (Ar+) that interact with hydrogen molecules. Interestingly, the ions seem to form predominately in the energetic regions of a supernova remnant, while hydrogen tends to dominate the outer reaches of the structure. Even so, they can sometimes interact to form compounds.

“But we soon realized that even in the Crab Nebula, there are places where the conditions are just right for a noble gas to react and combine with other elements. There, in the transition regions between ionized and molecular gas, argon hydride can form and survive,” Barlow concludes.