From UPSC perspective, the following things are important :
Prelims level : Helium hydride ion
Mains level : Formation of Elements
- Scientists have detected the most ancient type of molecule in our universe in space for the first time ever.
Helium hydride ion
- 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+.
- 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.
- Operating the GREAT spectrometer aboard SOFIA the team now reports the unequivocal detection of HeH+ towards the envelope of the planetary nebula NGC 7027.
- 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.
Importance of the discovery
- The chemistry of the universe began with HeH+.
- The lack of definitive evidence of its very existence in interstellar space has been a dilemma for astronomy for a long time.
- In the late 1970s, astro-chemical models suggested the possibility that HeH+ might exist at detectable abundances in local astrophysical nebulae.
- The discovery of HeH+ is a dramatic and beautiful demonstration of nature’s tendency to form molecules.
- It would be most easily observed in so-called planetary nebula, ejected by Sun-like stars in the last stage of their lifetime.
- The hard radiation field produced by the central white dwarf star with a temperature of more than 100,000 degrees drives ionization fronts into the ejected envelope, where HeH+ is predicted to form.
- The molecule will emit its strongest spectral line at a characteristic wavelength of 0.149 mm.