Dec. 12, 2013 — A molecule containing a noble gas has been discovered in space by a team including astronomers from Cardiff University.
visible light from the Crab Nebula seen by the Hubble Space Telescope.
This comes from emissions of gases in the nebula, which are energised by
the neutron star at the centre. In red, far infrared light seen by the
Herschel Space Observatory. This comes mainly from cold dust and gas.
(Credit: NASA, ESA, Alison Loll & Jeff Hester (University of
The find was made using a Cardiff-led instrument aboard Europe's
Herschel Space Observatory. The molecule, argon hydride, was seen in the
Crab Nebula, the remains of a star that exploded 1,000 years ago.
Before the discovery, molecules of this kind have only been studied in
laboratories on Earth.
The noble gases, which include helium, argon, radon and krypton,
usually do not react easily with other chemical elements, and are often
found on their own. In the right circumstances, however, they can form
molecules with other elements. Such chemical compounds have only ever
been studied in laboratories on Earth, leading astronomers to assume the
right conditions simply do not occur in space.
"The Crab Nebula was only formed 1000 years ago when a massive star
exploded," said 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."
Further measurements of the Crab Nebula were made using Herschel's
SPIRE instrument. Its development and operation was led by Professor
Matt Griffin, from the School of Physics and Astronomy. As molecules
spin in space, they emit light of very specific wavelengths, or colours,
called "emission lines." The precise wavelength is dictated by the
composition and structure of the molecule. Studying the emission lines
observed by the SPIRE instrument allows astronomers to study the
chemistry of outer space.
The team, led by Professor Mike Barlow from University College
London, did not set out to make the discovery, but stumbled upon it
almost by accident. "We were really concentrating on studying the dust
in the filaments with SPIRE, and out pops these two bright emission
lines exactly where we see the dust shining," says Dr Gomez. "The team
had a hard time figuring out what these lines were from, as no-one had
seen them before."
Professor Barlow said, "At first, the discovery of argon seemed
bizarre. 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
It now seems the Crab Nebula provides exactly the right conditions to
form such molecules. The argon was produced in the initial stellar
explosion, and then ionised, or energised, 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 ionised argon then
mixed with the cool gas to provide perfect conditions for noble gas
compounds to form.
The measurements allowed the team to gauge other properties in argon
molecules. "Finding this kind of molecule allowed us to evaluate the
type (or isotope) of argon we discovered in the Crab Nebula," said Dr
Gomez. "We now know that it is different from argon we see in rocks on
the Earth. Future measurements will allow us to probe what exactly took
place in the explosion 1000 years ago."
"What a great detective story," added Prof Matt Griffin, from Cardiff
University, and lead scientist of the team behind the SPIRE instrument.
"Here we see the excellent performance of the Herschel-SPIRE
spectrometer, the expertise of the instrument team in producing the
highest quality data, and the tenacity and vision of the scientists
analysing it, all coming together to make an intriguing new discovery."