Helonium: The First Molecule in the History of the Universe

Even before the formation of stars, planets, or the first atom of carbon, a strange and fragile molecule is thought to have emerged, from nothing but hydrogen and helium, the remnants of the Big Bang. The molecule is called helonium, and it is the story of nearly a century of laboratory chemistry, a discovery in 1925, and the now-landmark discovery in deep space in 2019 that finally substantiated what physicists had theorized for decades. This book explains why helonium is so significant to the study of the early universe, and how it was ultimately discovered in the cosmos after so many years of search.

What Is Helonium?

A Simple Formula With an Extraordinary Backstory

The common name for helium hydride ions is helium hydride, or “hydridohelium(1+)”. It’s a positive ion (cation) that’s made up of helium and a hydrogen atom with one electron stripped away. Its name is a typical chemical name; the name “helium” is followed by “-onium”, a suffix used by chemists to indicate a positively charged ion, as in more familiar ammonium.

The Lightest Heteronuclear Ion

Helonium is the lightest heteronuclear ion, that is, the smallest ion composed of two different elements linked together. It is so simple that it is scientifically very significant—the only elements involved are helium and hydrogen, both of which date back to the earliest times after the Big Bang; helonium is pretty close to the beginning.

Why Helonium Is Considered the First Molecule

Formed in the Chemistry of the Early Universe

Helonium is believed to be the first molecule to have been created in the universe, some 100,000 years after the Big Bang. The Universe at this time was almost pure hydrogen and helium—the two lightest and most abundant elements—with no other elements having yet been produced in the stars. Helium is the first element that could have formed a stable bond in that primordial environment and it was able to react with hydrogen to form helonium before any other molecular chemistry could occur.

A Different Kind of Periodic Table

Astronomers typically use a “simplified” version of the periodic table, one that includes only hydrogen, helium and all others put together, whatever these elements are in their actual form. Before the early universe created heavier elements by nuclear fusion, hydrogen and helium were the only elements at the disposal of chemists, and that’s why helonium’s simplicity makes it a perfect starting point for all subsequent molecular chemistry.

The 1925 Laboratory Discovery

Created in a Lab Decades Before Being Found in Space

Helonium was first synthesized in a lab in 1925 and was produced in space long before anyone found it there. That early “discovery” established the chemical reality of the ion and its stability to be studied, at least in isolation, for decades before it could be detected in the “cosmic web” of thousands of light-years of interstellar space.

Stable Alone, But Extremely Reactive

One of the more interesting features of helonium is that it’s stable when it’s isolated, but reacts very readily with almost any other molecule. This reactivity is what makes helonium impossible to prepare in large quantities in the laboratory as it will react to whatever it comes into contact with including the walls of the container, the presence of air molecules or any other material added to its container. It was the fragility that drove the effort to be sure of its presence in space.

The Decades-Long Search for Helonium in Space

A Theory Without Observational Proof

Helonium was known in the laboratory for almost 100 years, but was never found in the sky. It has also been theoretically predicted that it should exist somewhere in the universe, but, even though astronomers would have expected it to have formed many times in the early universe, there had been no evidence of its existence outside of the Earth’s laboratories for many decades.

Why Detection Was So Difficult

Helonium was also difficult to study due to its own reactivity, which made it difficult to study in bulk on Earth, and therefore hard to remotely detect with the light signatures detectable by astronomers. To identify a molecule this delicate, the cosmic environment had to be just right, in which helonium could not immediately react away, and the instruments had to be sensitive enough to pick up helonium’s spectral signature amidst the cacophony of all the other activity in the cosmic environment.

The 2019 Breakthrough Detection

Finally Found in the Planetary Nebula NGC 7027

Eventually, in 2019, scientists led by Güsten detected HeH+ in a planetary nebula, the NGC 7027 in Cygnus, about 3,000 light-years from the Earth. The discovery was published in the international journal Nature, and was an actual breakthrough in astrochemistry because it had been a long time since its prediction, which had been central to the models of chemistry in the early universe, had been validated.

Following in the Footsteps of Argonium

The detection of helonium is part of a similar discovery six years ago that argonium (ArgH+) was detected in the Crab Nebula, which was then hailed as the first naturally occurring noble gas molecule ever observed. This previous result with a similar noble-gas hydride ion bolstered the methods and theory for detecting noble-gas hydride ions, which would later be used to finally detect helonium in NGC 7027; two major achievements in astrochemistry in one decade.

Why Helonium Matters to Science Today

A Missing Piece in Models of the Early Universe

By confirming the existence of helonium in space, they not only answered the scientific question, but also confirmed that the universe’s chemistry processes they believed took place billions of years ago, actually took place. Helonium is at the very beginning of molecular chemistry, and the confirmation of its detection thus bolsters the confidence in the rest of the chain of chemical reactions that lead from simple molecules of hydrogen to the more complex chemistry found in the chemistry of stars, planets and all life here on Earth.

A Bridge Between Chemistry and Cosmology

Helonium is a molecule that is unusually simple to be completely understood in a laboratory, and yet is sufficiently important to tie in our understanding of the earliest moments of chemical history in the universe. It is part of the reasons for the 2019 discovery to attract so much attention among the scientific community, although helonium is a somewhat obscure term to most people who aren’t in the chemistry and astronomy field.

How Helonium’s Structure Works at the Atomic Level

Understanding the Bond Between Helium and Hydrogen

Helonium may also be considered as a protonated helium atom, that is, a helium atom with an additional proton attached to it from some source of hydrogen. Normally one of the most inert elements on the whole periodic table, helium is a noble gas which is highly resistant to bonding under almost any normal conditions on Earth. The reason helonium can happen is because it’s a tailored, high-energy environment where that bond is forced into existence, something that is quite different from a standard laboratory or environment that most people experience.

Why Noble Gas Chemistry Is So Unusual

Noble gases such as helium and argon are in a special group because they normally don’t bond with other atoms, and their electron configurations are already stable without sharing or exchanging electrons with surrounding atoms. Helonium and its cousin argonium are among the few exceptions, which can only be produced under extreme conditions – in a space that is not just a laboratory or a small controlled facility – they are found only in nature in space, which is why the researchers involved were so impressed with this discovery.

Helonium in Popular Culture and Wordplay

A Word That Shows Up Beyond Chemistry

Helonium has also sometimes made the transition into pop culture and gaming, being used as an item or resource name in a number of online games that refer to the actual chemical ion for its creative inspiration rather than actual use. This sort of crossover is not very unusual for a word that has a vague and evocative and catchy scientific sound to it; helonium, for instance, evokes the flavour of science fiction and fantasy, even though in truth it’s not anything actually related to the chemistry behind the main substance.

Not a Valid Scrabble Word, But a Real Chemical Term

Helonium is a perfectly valid word in scientific terms, but is not in any valid word list, such as the North American or international Scrabble dictionaries. It’s a nice reminder that a word’s inclusion in a dictionary-based word game doesn’t necessarily mean it is a legitimate word in the dictionary nor a legitimate chemical or scientific term, and helonium is a good example of one that is a real chemical or scientific term, but not a word in the dictionary game.

What Helonium Teaches Us About Scientific Patience

A Nearly Century-Long Wait for Confirmation

It took almost 100 years for helonium to be discovered by a laboratory in 1925 and then be definitively detected in space in 2019. It is not that the science itself has been proved incorrect, but indeed because it takes decades to build instruments sensitive enough to test theoretical predictions, and decades more to secure the funding for such instruments, and decades more to make scientific progress that enables the development of such instruments.

A Model for How Science Confirms Its Own Theories

Rather, the long period of time also gives some insight into the nature of scientific practice: theories that are accepted by most scientists are not necessarily observationally confirmed, and serious scientists take that distinction seriously. This is a pretty pure example of the scientific process in action, and it came out exactly like it was supposed to—with a confident prediction, a lab demonstration, and finally, an astronomical confirmation that took much longer than anyone originally thought.

Final Thoughts

Not many molecules have the scientific clout as helonium, a simple and delicate structure formed from the universe’s two lightest elements that may have initiated all molecular chemistry as we know it today. Helonium’s story from discovery in the laboratory in 1925 to its much-anticipated discovery in the depths of NGC 7027 in 2019 is a testament to the fact that sometimes, the most important science breakthroughs come when the scientists have finally confirmed what they already knew was there in the first place, after all the theory, and after all the years of waiting.

Frequently Asked Questions

What is helonium made of?

Helonium or HeH+ consists of one helium atom and one hydrogen atom with the removal of one electron, leading to a positive charge.

When was helonium first discovered?

It was first made in a laboratory in 1925, but wasn’t found in space until 2019.

Why is helonium considered the first molecule in the universe?

It is believed to be created about 100,000 years after the Big Bang when there was hydrogen and helium only, and thus is the oldest possible molecule combination.

Where was helonium finally detected in space?

As reported in Nature 2019, in the planetary nebula NGC 7027 (the Secretariat) in the constellation Cygnus, approximately 3,000 light-years from Earth, the researchers observed a quasar and a radio source.

Why is helonium so hard to study?

It is very reactive and cannot be made in large quantities because it reacts with virtually any other molecule it comes into contact with in as near to real-time as possible.