Not long after the Big Bang, chemistry as we know it took its first baby steps
William B. Latter/SIRTF Science Center/Caltech, NASA, ESA
Helium hydride ions, thought to be the first type of molecule to form in the universe, have finally been spotted in space.
These charged molecules, each made of a neutral helium atom and a positively charged hydrogen atom, first emerged within about 100,000 years after the Big Bang. Back then, the universe was composed almost entirely of hydrogen and helium, and helium hydride was the only molecule that these two elements could create when they collided.
Although researchers have seen helium hydride ions in the lab, these molecules have never been definitively detected in space. The discovery of helium hydride in a nearby planetary nebula ends a decades-long search for these seminal molecules and helps confirm our understanding of chemistry in the infant universe, researchers report online April 17 in Nature.
During three flights in May 2016, the airborne Stratospheric Observatory for Infrared Astronomy observed a planetary nebula about 3,000 light-years away called NGC 7027. This shell of stellar material was blown off a sunlike star when its core collapsed into a white dwarf about 600 years ago. In the light emitted by the hot, dense cloud of gas, researchers detected helium hydride’s signature wavelength of infrared radiation.
The helium hydride ions seen in NGC 7027 were created in the planetary nebula, rather than being leftover from the early universe. But their existence confirms that helium hydride ions can exist outside the lab, which means that theoretical simulations of the primordial cosmos aren’t in serious need of revision.
Adam Perry, who studied helium hydride while at the University of Illinois Urbana-Champaign, likens the new find to unearthing a fossil that fills a missing link in animal evolution. “Everybody knew [helium hydride] had to be out there,” says Perry, who wasn’t involved in the study. But “where before there wasn't any hard evidence, now there is.… People who do astrochemistry are going to be very excited about this.”
Studying the helium hydride ions in NGC 7027 may offer new insights into the chemical reactions that form these ions, says study coauthor Rolf Güsten, an astrophysicist at the Max Planck Institute for Radio Astronomy in Bonn, Germany.
Güsten and colleagues also hope to use the Atacama Large Millimeter/submillimeter Array in northern Chile to scour the distant, early universe for helium hydride ions born soon after the Big Bang.
R. Güsten et al. Astrophysical detection of the helium hydride ion HeH+. Nature. Published online April 17, 2019. doi:10.1038/s41586-019-1090-x.
R. Cowen. Chemistry of the Cosmos: Quasars illuminate the young universe. Science News. Vol. 163, May 3, 2003, p. 278.