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HeH+: Universe’s first molecule detected in space

Date: 20 April 2019 Tags: Space

Scientists for the first time ever have detected Universe’s most ancient type of molecule- Helium hydride ion (HeH+) in space. It was discovered in the envelope of planetary nebula NGC 7027 using GREAT spectrometer aboard onboard the flying observatory SOFIA.

Helium hydride ion (HeH+)

It was first molecule that formed almost 14 billion years ago, when temperatures of young universe had fallen below 4000 Kelvin. This had allowed recombination of light elements (hydrogen, helium, deuterium and traces of lithium) produced in Big Bang. At that time, ionized hydrogen and neutral helium atoms reacted to form HeH+ through process of nucleosynthesis in reverse order of their ionization potential.

In this process, Helium first combined with free electrons to form first ever neutral atom. During this time, hydrogen was still ionized or present in form of bare protons. Helium atoms combined with these bare Hydrogen protons resulting in formation of helium hydride ion HeH+, the universe’s first molecular bond.

As further this recombination process progressed, HeH+ reacted with then neutral hydrogen and created first path to formation of molecular hydrogen — marking beginning of modern universe.

Significance of this discovery

Despite importance of HeH+ in history of the early Universe, it has so far escaped detection in astrophysical nebulae — cloud of gas and dust in outer space.  The lack of definitive evidence of its very existence in interstellar space was dilemma for astronomy for long time. The discovery is demonstration of nature’s tendency to form molecules.