Crab Nebula Surprises Astronomers With Noble Gas Molecules
December 13, 2013

First-Ever Noble Gas Molecules Discovered In Space

[ Watch the Video: Supernova Remnant Shows Signs Of Noble Gas ]

redOrbit Staff & Wire Reports - Your Universe Online

Astronomers from the UK have discovered argon hydride within the Crab Nebula, marking the first time that noble gas molecules have been detected in space, according to research appearing in Friday’s edition of the journal Science.

As part of their study, Mike Barlow of the University College London Department of Physics and Astronomy and his colleagues used the ESA’s Herschel Space Observatory to observe the supernova remnant in far infrared light, the school explained in a statement.

By measuring areas of cold gas and dust, they were able to discover the chemical fingerprint of argon hydride ions, the university added. Their findings helped support existing theories as to how argon forms in nature.

“We were doing a survey of the dust in several bright supernova remnants using Herschel, one of which was the Crab Nebula,” Barlow said, adding that the discovery was “unexpected” because they did not expect argon “to form molecules, and you wouldn't expect to find them in the harsh environment of a supernova remnant.”

The noble gases, which also include helium and radon, typically do not react easily with other chemical elements, and as such are typically found on their own. However, the study authors report that the gases can form molecules under the right circumstances. Since these chemical compounds had only ever been studied in laboratories on Earth, astronomers believed that the right conditions for their formation did not exist in space.

“The Crab Nebula was only formed 1000 years ago when a massive star exploded,” explained Dr. Haley Gomez of Cardiff University's School of Physics and Astronomy. “Not only is it very young in astronomical terms, but also relatively close, at just 6,500 light years away, providing an excellent way to study what happens in these stellar explosions.”

“Last year, we used the European Space Agency's Herschel Space Observatory to study the intricate network of gas filaments to show how exploding stars are creating huge amounts of space dust,” she said, adding that additional measurements of the Crab Nebula were completed using the telescope’s SPIRE instrument, which helps researchers study wavelengths of light (known as “emission lines”) to help determine the chemistry of space.

Gomez said that the team was focusing on analyzing dust in the filaments using SPIRE, when they found two bright emission lines at the same place where they witnessed dust shining. She said that none of the researchers had seen anything like that before, and as such they had difficulty determining where the lines came from.

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

“It now seems the Crab Nebula provides exactly the right conditions to form such molecules,” Cardiff University added. “The argon was produced in the initial stellar explosion, and then ionized, or energized, with electrons stripped from the atoms in resulting intense radiation as shockwaves. These shockwaves led to the formation of the network of cool filaments containing cold molecular hydrogen, made of two hydrogen atoms. The ionized argon then mixed with the cool gas to provide perfect conditions for noble gas compounds to form.”

Image 2 (below): Herschel image and spectrum of the Crab Nebula, with emission lines from the molecular ion argon hydride. Credit: ESA/Herschel/PACS, SPIRE/MESS Key Programme Supernova Remnant Team