Oldest molecules in the universe found

Helium hyride in planetary nebula 7027
Image of planetary nebula NGC 7027 with an illustration of helium hydride molecules. In this planetary nebula, SOFIA detected helium hydride, a combination of helium (red) and hydrogen (blue),This is the first time helium hydride has been found in the modern universe. Credits: NASA/ESA/Hubble Processing: Judy Schmidt

The T.C. Team

Yes, scientists have found the first molecules that may have ever formed in the universe. And no, not in some galaxy far, far away, but in our own backyard, figuratively speaking – a trip of a mere 3,000 light years.

The abstract about their work in Nature opened almost poetically.

“During the dawn of chemistry, when the temperature of the young Universe had fallen below some 4,000 kelvin [6700 F],” it began, before talking of how the lightest elements produced after Big Bang and their charged variants recombined with each other.

The early universe had very small atoms – hydrogen and helium being the primary products. Often they lacked sufficient electrons, the negatively charged particles orbiting a clump of the positively charged protons and the neutral, well, neutrons. As long as the number of protons and electrons in an atom were equal, it has neutral charge.

SOFIA carrying GREAT
The SOFIA photographed during nighttime operations prior to flying with the GREAT instrument installed on the airborne observatory. Pic, NASA Photo / Tom Tschida

Helium tends to get to neutral quickly by sopping up elections – in a way lighter hydrogen cannot. But in the absence of much other material to work with in the immediate post-Big Bang era, neutral helium bonded with a positive hydrogen ion (a proton-neutron nucleus minus the negatively charged electron). The result was the unstable HeH+, that is helium hydride that slowly recombined to form helium and hydrogen molecules.

Of course the early material was pulled together by gravity that ultimately set them aflame as stars. Considerable bumping and grinding pushed these light atoms together to form larger ones within those stars, and much larger ones when stars either exploded or smashed into each other.

For the moment, the theory about helium hydride being the first molecules was all good. It had even been created in the laboratory back in 1925. But for long there was no evidence of it lingering on anywhere in the cosmos.

Then came SOFIA – the Stratospheric Observatory for Infrared Astronomy, carried by an aircraft at 45,000 feet. That height is a little above what most aircraft fly, and certainly clear of atmospheric phenomena. SOFIA had the advantage of being able to come down to earth for changes in equipment in a way an observatory in orbit could not.

“We’re able to change instruments and install the latest technology,” Naseem Rangwala, a SOFIA deputy project scientist, told nasa.org. “This flexibility allows us to improve observations and respond to the most pressing questions that scientists want answered.”

Rolf Guesten and Urs Graf
Rolf Guesten, left, and GREAT team member Urs Graf, discuss preparations for the flights with the instrument. Pic, NASA Photo / Tom Tschida

That latest tech was the German Receiver for Astronomy at Terahertz Frequencies (oh, GREAT), which is a sensitive spectrometer. A spectrometer gauges the composition of stars or other objects based on the light they project.

With new equipment included, SOFIA went up again only to find that helium hydride certainly did exist in NGC 7027, a planetary nebula. A planetary nebula is the expanding mass of charged gas around an aging red giant.

“The lack of evidence of the very existence of helium hydride in interstellar space was a dilemma for astronomy for decades,” Rolf Guesten, the first author on the paper, was quoted as saying by nasa.org. Guesten, of the Max Planck Institute for Radio Astronomy, in Bonn, Germany, was the lead author of the piece.

“It was so exciting to be there, seeing helium hydride for the first time in the data,” Guesten continued. “This brings a long search to a happy ending and eliminates doubts about our understanding of the underlying chemistry of the early universe.”

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