Early Conditions in the Universe

In the first few seconds after the Big Bang, the universe was incredibly hot – too hot for atoms to form stably on their own. It wasn’t until around 20 minutes after the Big Bang that temperatures cooled enough for helium atoms to form. Around 25% of all matter in the universe is helium today.

However, even after 20 minutes, temperatures were still too warm for individual atoms to combine into molecules. The early universe consisted of neutral hydrogen and helium atoms floating alone in the hot plasma. Hydrogen atoms could not stably combine with each other to form the hydrogen molecule, H2.

Formation of Helium Hydride

For the universe to cool enough to form molecules, scientists theorized another molecule must have formed first to help kickstart the process. This molecule was helium hydride, also known as HeH+.

Helium hydride was believed to exist in the early universe around 100,000 to 377,000 years after the Big Bang. Its existence was necessary for hydrogen molecules (H2) to form. Helium hydride interacts with single hydrogen atoms, adding a second hydrogen to make H2 molecules.

Helium hydride was first artificially created in the lab in 1925. However, it can only exist in extreme conditions similar to the early universe, with a lot of heat. At normal temperatures and pressures, it is too unstable and reacts rapidly with other substances.

Detection of Helium Hydride

The Sofia Telescope

In 2022, astronomers were able to detect helium hydride for the first time in space, confirming its role in the early universe. They used the Stratospheric Observatory for Infrared Astronomy (SOFIA) telescope to make the discovery.

SOFIA is a 2.7 meter infrared telescope aboard a modified Boeing 747SP jetliner, operated jointly by NASA and the German Aerospace Center. Flying in the stratosphere at altitudes of up to 45,000 feet, SOFIA has a clear view of the skies without 95% of the obscuring atmosphere below. It can also be repositioned to observe different regions of the sky.

Using SOFIA, scientists detected a spectral line signature that matched what would be expected from helium hydride. The molecule was found inside the planetary nebula NGC 7027, located around 3,000 light years from Earth.

Properties of Helium Hydride

Helium hydride is an extremely reactive molecule. It is considered the strongest acid that exists, able to react even with helium which is normally a noble gas.

The only way scientists have been able to contain helium hydride in the lab is by constantly producing new molecules. There is no way to store it, as it will immediately destroy any container by reacting with the material.

Its extreme reactivity helps explain why helium hydride cannot exist on Earth today outside of the specialized conditions it was first created in. However, inside the hot gases of NGC 7027, conditions mimic those of the early universe allowing the molecule to form.

Significance of Finding Helium Hydride

The detection of helium hydride inside NGC 7027 provides strong evidence that supports theories about molecular formation in the early universe. Scientists had predicted that helium hydride must have existed based on what is needed to form other molecules like hydrogen gas.

Finding helium hydride in the location it was predicted to be further confirms our understanding of universal evolution following the Big Bang. The early universe conditions required for helium hydride to form over 13 billion years ago still exist inside the planetary nebula.

The discovery answers long-standing questions about how the first steps in molecular chemistry occurred after the Big Bang. Helium hydride helped hydrogen atoms combine, without which star and planet formation may not have been possible. Its detection marks the first direct observation of a molecule from the early universe.