In the beginning, there were no molecules. For hundreds of thousands of years after the big bang, the universe was too hot and full of radiation for atoms to bond together聽鈥� but now, for the first time, we have spotted the first type of molecule to arrive on the scene.
Just after the big bang, there were only three kinds of atoms: the three lightest elements: hydrogen, helium and lithium. Temperatures throughout the universe were in the thousands of degrees, and harsh UV radiation made it difficult for atoms to stick together to form molecules. When things finally calmed down enough, nearly 400,000 years after the big bang, theoretical chemistry tells us that the first molecule to form was a combination of a helium atom and a hydrogen ion. The product of this union is called a helium hydride ion.
For decades, astronomers have tried and failed to find any definitive trace of helium hydride ions in space, but now David Neufeld at Johns Hopkins University in Maryland and his colleagues have finally spotted them.
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They used a detector on-board the Stratospheric Observatory for Infrared Astronomy (SOFIA), a telescope on an aeroplane that flies high in atmosphere. Because SOFIA flies so high, there is little water vapour that blocks the infrared light from ions in space and makes them difficult to detect using ground-based telescopes.
Neufeld and his colleagues found signs of an area with about 3000 helium hydride ions per cubic metre in the planetary nebula NGC 7027. This sits some 3000 light years from us, and is home to one of the hottest stars we have ever seen.
鈥淲e haven鈥檛 detected those helium hydride molecules that were the first in the universe, they鈥檙e lost in the sands of time,鈥� says Neufeld. Instead, he says, they have detected the same type of molecule in the relatively recent past 鈥� from just 3000 years ago, because that is how long it would take light from the nebula to reach us.
Because the conditions in this sweltering-hot cloud of gas are similar to those in the early universe, this is a sign that our understanding of the chemistry back then is correct, he says. 鈥淚t basically helps confirm that we have some understanding of interstellar chemistry,鈥� says Neufeld. 鈥淚t鈥檚 the tendency for molecules to form in the most unlikely and harsh environments that makes it very cool to me.鈥�
Nature
