- Researchers detected the first kind of molecule formed in the Universe, using NASA’s airborne observatory SOFIA.
- They found helium hydride in a very young and dense planetary nebula located 3,000 light-years from Earth.
The early stages of the Universe consisted of limited types of atoms. Nearly 100,000 years after the Big Bang, helium and hydrogen merged to form a molecule named helium hydride for the first time.
The helium ions He+ and He2+ were the first ions to merge with free electrons, creating the first neutral atoms, followed by the recombination of hydrogen. In low-density and metal-free environment, neutral atoms of helium created the Universe’s first molecular bond in the HeH+ through radiative association with protons. As these ions recombined, they destroyed HeH+, creating a path to the formation of molecular hydrogen.
Now, scientists have discovered this molecule in space for the first time, after decades of observations and studies. They have found the signature of helium hydride in the Milky Way galaxy using the NASA’s airborne observatory SOFIA (short for Stratospheric Observatory for Infrared Astronomy).
Today’s universe is filled with massive, complex structures like galaxies, stars, and planets. However, the early universe — thousands of years after the Big Bang — was too hot and contained only a few kinds of atoms, mostly hydrogen and helium.
As these elements merged to create the first molecules (helium hydride), our universe began to cool and take shape. Then atoms of hydrogen interacted with this first primordial molecules, triggering the formation of molecular hydrogen which ultimately created the first stars in the universe. Stars then forged all the atoms and molecules that make up the complex chemical cosmos of today.
Until now, scientists haven’t been able to detect helium hydride in interstellar space, the very first stage of the birth of chemistry.
Since helium is a noble gas, it hardly merges with other atoms. However, a research team in 1925, created a helium hydride molecule in a lab: they coaxed the helium atom to share one of its electrons with a hydrogen ion H+.
The Right Equipment In The Right Position
In the late 1970s, astronomers explored a very young and dense planetary nebula named NGC 7027. It is located 3,000 light-years from Earth in the constellation Cygnus. They found that the nebula hosts a perfect environment for forming helium hydride. UV rays and heat from the old star create suitable conditions that enable this mystery molecule to form.
The space telescopes do not have the particular technology to capture signs of helium hydride and differentiate them from other molecules in the dense planetary nebula. That’s why researchers used SOFIA to make observations above the Earth’s atmosphere.
SOFIA is Boeing 747SP aircraft specifically designed to carry a 2.7-meter reflecting telescope. It can make observations while flying at 45,000 feet into the stratosphere. This blocks 99% interference from Earth’s infrared atmosphere and allows researchers to effectively explore the solar system and beyond.
NGC 7027 with illustration of molecules of helium hydride | Credits: NASA/ESA/Judy Schmidt
Unlike space-based telescopes, the instruments and technology on SOFIA can be updated regularly, as it returns to ground after every flight. This flexibility enabled researchers to enhance their observations and solve the decades-old mystery.
One of the recent upgrades on SOFIA’s equipment named GREAT (short for German Receiver at Terahertz Frequencies) added certain channels for helium hydrides which aren’t available on existing space-based telescopes.
Like tuning a radio to the right station, researchers tuned to the helium hydride frequency and recorded the data in real time. The signals came through loud and clear, helping them understand the underlying chemistry of the young universe.