In the beginning, there was a big bang. And then, around 100,000 years later, helium and hydrogen combined for the first time to create a molecule called helium hydride. For the first time in history scientists have detected helium hydride, offering a direct connection to the earliest days of the universe.
While it may not present the photo opportunities of a black hole, helium hydride has been crucial in the formation of the known universe. When it was first forming, there wasn't much of a universe yet and it was all extremely hot, with helium and hydrogen constantly bumping into each other. Only when helium hydride started forming could the universe cool down and expand. Later, cooled helium would interact with helium hydride and create molecular hydrogen, a crucial ingredient in the development of stars.
That's been the longtime theory, at least. But this theory, which tracks the very earliest moments of chemistry in history, has been unproven until now.
“The lack of evidence of the very existence of helium hydride in interstellar space was a dilemma for astronomy for decades,” says Rolf Guesten of the Max Planck Institute for Radio Astronomy, in Bonn, Germany, and lead author of the paper, in a press statement.
The dilemma was solved by NASA’s Stratospheric Observatory for Infrared Astronomy, or SOFIA. The world’s largest airborne observatory, SOFIA is an 80/20 partnership of NASA and the German Aerospace Center (DLR). It's an airplane—an extensively modified Boeing 747SP aircraft carrying a 2.7-meter (106 inch) reflecting telescope.
Helium hydride has long presented challenges to scientists. In the late 1970s, while studying a planetary nebula called NGC 702, a growing suspicion formed that it could be a cradle for this earliest of molecules. But nothing, not even space telescopes, could clear the noise of the nebula for the specific signal of helium hydride.
So scientists turned to SOFIA. The plane flies at 45,000 feet, above the interfering layers of the Earth's atmosphere. While it can't get as close to objects in space as the Hubble, it does have one serious advantage—it can come back to Earth. That means scientists can make adjustments based on why they are searching the skies.
“We’re able to change instruments and install the latest technology,” says Naseem Rangwala SOFIA deputy project scientist. “This flexibility allows us to improve observations and respond to the most pressing questions that scientists want answered.”
One of those instruments is known as the German Receiver at Terahertz Frequencies, or GREAT. Scientists were able to alter GREAT by adding a channel specifically geared towards helium hydride. Similar to a radio receiver, GREAT was able to tune into the frequencies generated by helium hydride molecules.
“It was so exciting to be there, seeing helium hydride for the first time in the data,” said Guesten. “This brings a long search to a happy ending and eliminates doubts about our understanding of the underlying chemistry of the early universe."