First molecular bond in the universe found at last
Long theorised but never observed, helium hydride has now been observed in a young nebula. Andrew Masterson reports.
What is thought to be the first molecular bond ever formed in the universe has been detected for the first time – in a young planetary nebula 3000 light-years from Earth.
The discovery – which adds strong evidence to the standard model describing the events soon after the Big Bang – is reported in the journal Nature.
In one sense, the chemistry of the immediate post Big Bang period, around 14 billion years ago, is simple. First came ions for only the lightest of the elements – hydrogen and helium primarily, with trace amounts of lithium and beryllium.
As the temperature began to fall towards 4000 degrees Kelvin, these ions began to combine with free electrons to form neutral atoms. After that, neutral helium atoms hooked up with a proton to form helium hydride – the first molecular bond in the history of the universe.
It was a transient marriage, with the bond resulting in the destruction of the helium hydride and setting the chemical scene for the creation of molecular hydrogen.
So far, so straightforward, but although the molecular combination was isolated in a laboratory as early as 1925, it has never been observed in space – until now.
Researchers led by Rolf Güsten, from Germany’s Max Planck Institute for Radioastronomy in Bonn, Germany, report the successful detection of the elusive ion in a distant planetary nebula called NGC 7027.
The discovery was made after Güsten and colleagues analysed data gathered in 2016 by a high-resolution spectrometer on board a flying facility known as the Stratospheric Observatory for Infrared Astronomy (SOFIA) a joint venture between NASA and the German Aerospace Centre.
NGC 7027 was a prime target in the hunt for helium hydride because it is a very young nebula and has chemical conditions, therefore, moderately similar to those that pertained in the early universe.
In the modern world, the researchers say, the molecular bond is of only limited importance. However, “the chemistry of the universe began with this ion”.
“The lack of definitive evidence for its very existence in interstellar space has been a dilemma for astronomy,” they write.
“The unambiguous detection reported here brings a decades-long search to a happy ending at last.”