Most ancient type of molecule in our universe

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Topics Covered:

  1. Awareness in space.

 

Most ancient type of molecule in our universe

 

What to study?

For Prelims and Mains: Helium hydride ion- discovery and significance.

 

Context: Scientists have detected the most ancient type of molecule in our universe- Helium hydride ion– in space for the first time ever.

  • It was discovered with the help of the GREAT spectrometer aboard SOFIA in the envelope of the planetary nebula NGC 7027.
  • Despite its importance in the history of the early Universe, HeH+ has so far escaped detection in astrophysical nebulae — cloud of gas and dust in outer space.

 

Key findings:

Helium hydride ion (HeH+) was the first molecule that formed when, almost 14 billion years ago, falling temperatures in the young universe allowed recombination of the light elements produced in the Big Bang. At that time, ionized hydrogen and neutral helium atoms reacted to form HeH+.

 

How and when was it formed?

  • During the dawn of chemistry when the temperature in the young universe had fallen below 4000 Kelvin, the ions of the light elements (hydrogen, helium, deuterium and traces of lithium) produced in Big Bang nucleosynthesis recombined in reverse order of their ionization potential.
  • Helium combined first with free electrons to form the first ever neutral atom. At that time hydrogen was still ionized or present in form of bare protons. Helium atoms combined with these protons into the helium hydride ion HeH+, the universe’s first molecular bond.
  • As recombination progressed, HeH+ reacted with then neutral hydrogen and created a first path to the formation of molecular hydrogen — marking the beginning of the modern universe.

 

Background:

The lack of definitive evidence of its very existence in interstellar space has been a dilemma for astronomy for a long time. The discovery of HeH+ is a dramatic and beautiful demonstration of nature’s tendency to form molecules.

 

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