When the universe formed during the Big Bang 13.8 billion years ago, the chemical reactions of the aftermath formed the first molecules. Those first molecules were crucial in helping form everything we know, but they're also absent.
And although HeH+, the helium hydride ion, has been proposed for years as that first molecule, scientists couldn't find any evidence of its existence in space -- until now. The findings were published Wednesday in the journal Nature .
After the Big Bang, HeH+ formed in a molecular bond when helium atoms and protons combined. Later, these would break apart into hydrogen molecules and helium atoms. Both elements are the two most abundant throughout the universe, with hydrogen first and helium second.
Scientists were able to demonstrate the molecular ion in a lab in 1925 and study it, which sparked a decades-long search for HeH+ in space.
"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," said Rolf Güsten, study author and astronomer at the Max Planck Institute for Radioastronomy, in a statement.
Astrochemical models in the late 1970s pointed to a detectable possibility. This led scientists to believe that HeH+ might exist in the chaotic planetary nebula ejected by stars like our sun during the last stage before they explode in a supernova.
The molecular ion is formed when the radiation of the star, reaching temperatures more than 100,000 degrees, ionizes the nebula.
But detecting the molecule's signal at its strongest wavelength has been difficult. The opaqueness of Earth's atmosphere rules out any ground-based telescopes.
So researchers used SOFIA, the Stratospheric Observatory for Infrared Astronomy, a modified Boeing jet carrying a telescope that can fly above the lower atmosphere.
A high-resolution spectrometer called GREAT on board SOFIA detected the molecule in the planetary nebula NGC 7027.
"The discovery of HeH+ is a dramatic and beautiful demonstration of nature's tendency to form molecules," said David Neufeld, study co-author and professor in the Physics and Astronomy Department at Johns Hopkins University, said in a statement.
"Despite the unpromising ingredients that are available, a mixture of hydrogen with the unreactive noble gas helium, and a harsh environment at thousands of degrees Celsius, a fragile molecule forms. Remarkably, this phenomenon can not only be observed by astronomers but also understood using theoretical models that we have developed."