About ten seconds after the big bang, the relatively small but rapidly expanding universe consisted of atomic nuclei, electrons and photons all floating freely in a superheated plasma. Eventually things cooled enough for these particles to form stable atoms, and the universe was filled with mostly hydrogen and helium. Some 100,000 years into the history of the universe, atoms finally combined to form the first molecules—neutral helium atoms combined with positively charged hydrogen atoms to form the molecule helium hydride.
Helium hydride has long been thought to be the beginning of a long chain of chemistry that ultimately led to all the diverse molecules of the universe, and for the first time, scientists have spotted the molecules in space. Astronomers using NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), an infrared telescope mounted on a Boeing 747, discovered modern helium hydride in a planetary nebula in our own galaxy, as detailed in a study published this week in Nature.
“Although HeH+ [helium hydride] is of limited importance on Earth today, the chemistry of the universe began with this ion,” the authors write in the study. “The lack of definitive evidence for its very existence in interstellar space has been a dilemma for astronomy. The unambiguous detection reported here brings a decades-long search to a happy ending at last.”
SOFIA took three flights in May 2016, climbing as high as 45,000 feet, to observe the planetary nebula NGC 7027, Maria Temming reports for Science News. Positioned about 3,000 light-years away, the planetary nebula is an expanding cloud of gas surrounding a star that was once similar to the sun but has ejected most of its material, leaving behind a stellar remnant called a white dwarf. Within the hot gas of the nebula, SOFIA was able to pick out the signature of helium hydride in infrared light.
“This molecule was lurking out there, but we needed the right instruments making observations in the right position—and SOFIA was able to do that perfectly,” says Harold Yorke, director of the SOFIA Science Center in California, in a statement from NASA.
Helium hydride is not a particularly stable molecule, but scientists were able to create the positively charged ion in the lab in 1925, reports Bill Andrews for Discover. Astronomers have hoped to find the molecule in a nebula for decades, and in the 1970s, observations of NGC 7027 suggested that it might have the right conditions—high heat and large amounts of ultraviolet radiation—for helium hydride to form.
More recently, an upgrade to one of SOFIA’s instruments, the German Receiver at Terahertz Frequencies (GREAT), allowed the airborne telescope to search for the wavelength of light emitted by helium hydride ions. The instrument works like a radio receiver, according to the NASA statement, and telescope operators can tune to the correct frequency to search for specific molecules.
The helium hydride observed by SOFIA was formed in NGC 7027, long after the first molecules were created more than 13 billion years ago. But the lead author of the new study, Rolf Güsten of the Max Planck Institute for Radio Astronomy in Germany, and his team plan to use the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to search for helium hydride that was created shortly after the big bang. If they are successful, humanity will have peered back in time billions of years and spotted some of the first building blocks of everything that was to come.