For a long time now, scientists have considered helium hydride to represent the first-ever molecular bond and chemical compound in the universe, hypothesised to have formed when a helium atom shared its electrons with a hydrogen nucleus.
And even though it was actually synthesised in the lab in 1925, detecting it in space under free-range conditions in gas clouds proved elusive, thereby pushing back the hopes of researchers to add support to various hypotheses about primordial chemistry after the big bang.
“Although [helium hydride] is of limited importance on Earth today, the chemistry of the universe began with this ion,” wrote the authors of a new paper in the journal Nature. “The lack of definitive evidence for its very existence in interstellar space has been a dilemma for astronomy.”
Now, culminating the decades-long search – which mostly turned up large organic molecules, but not helium hydride – a group of experts claim to have detected the presence of the molecule in a 600-year-old planetary nebula called NGC 7027 and located about 3,000 light years away in the constellation of Cygnus.
“This molecule was lurking out there, but we needed the right instruments making observations in the right position – and SOFIA [Stratospheric Observatory for Infrared Astronomy] was able to do that perfectly,” said Harold Yorke, Director of the SOFIA Science Centre in California’s Silicon Valley.
Search of the NGC 7027 began in the 1970s, as researchers thought it might be a likely place for the molecule to exist in the modern universe. Unfortunately, the technology used for the search was simply not advanced enough to pick up on the right signature among the medley of other molecules also present in the nebula.
With the recent upgrade to one of SOFIA’s instruments called the German Receiver at Terahertz Frequencies, or GREAT, which added a helium hydride channel which previous telescopes did not have, the team was able to zero in on the signal loud and clear.
“It was so exciting to be there, seeing helium hydride for the first time in the data,” said lead author Rolf Guesten of the Max Planck Institute for Radio Astronomy. “This brings a long search to a happy ending and eliminates doubts about our understanding of the underlying chemistry of the early universe.”