There were no galaxies, stars, or even molecules in the eons following the Big Bang. There were, however, plenty of atoms. With an entire universe of mass in atomic form, it was only a matter of time until the first molecules formed. Scientists have long suspected that helium hydride was the first molecule in the universe, but no one has ever detected it in space until now. NASA researchers have spotted helium hydride many light years away in a planetary nebula.
Scientists working on NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) have now confirmed the existence of helium hydride in the planetary nebula NGC 7027. This cloud of dust and gas, the remnant of a sun-like star that perished ages ago, is 3,000 light-years away in the constellation Cygnus.
The early universe was too hot for anything other than helium and hydrogen atoms to exist. Scientists estimate it took about 100,000 years for the universe to cool enough for the first molecules to form. It makes sense those first molecules would be helium hydride, and it would have been essential in the formation of the first stars. As the universe cooled, hydrogen would have been able to interact with helium hydride, generating the molecular hydrogen that gave rise to the first stars. In stars, hydrogen is fused into all the heavier elements we see in the modern universe.
NASA describes helium hydride as “finicky.” Helium is a noble gas that rarely combines with other elements. However, experiments decades ago showed it was possible to create helium hydride, but the conditions necessary to generate the molecule naturally are rare indeed. Astronomers have long suspected NGC 7027 would have just the right combination of ultraviolet radiation and heat.
To lessen interference from Earth’s atmosphere, SOFIA’s instruments were integrated with a Boeing 747SP aircraft that can fly at 45,000 feet. The 106-inch telescope recently received an upgraded instrument called the German Receiver at Terahertz Frequencies, which added the necessary channel to scan for helium hydride. When astronomers pointed it at NGC 7027, the helium hydride signal came through clear as day.
Confirming the existence of helium hydride where scientists predicted is an important step toward understanding the early universe. We can now focus on exploring other predictions with greater confidence.
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