Atomic secret of star formation uncovered

Astronomers have discovered new information regarding the role of hydrogen atoms in stellar formation. Hydrogen molecules are thought to fuel star formation, but this new research shows there are more hydrogen atoms than molecules – even in young star-producing galaxies. In the Milky Way, almost 70% of hydrogen gas is found in individual atoms, while the rest are in molecules.

Astrophysicist Dr Luca Cortese, from the International Centre for Radio Astronomy Research (ICAR), in Australia said: “New stars are born in dense clouds of gas and dust that are found in most galaxies. Our own Milky Way forms about one new star a year on average.”

Astronomers expected to see younger galaxies containing more molecular hydrogen as they looked back in time, however atomic hydrogen makes up the majority of gas in younger galaxies too. This was found to be true even in galaxies under conditions similar to those occurring in what is known as a cosmic noon – a period seven billion years after the Big Bang when stellar formation reached its peak.

Over the last 10 years, astronomers have discovered young, star-forming galaxies at cosmic noon with 10 times more hydrogen molecules than the Milky Way. Now, Dr Cortese and his team have discovered a cluster of galaxies 3billion years younger. These galaxies were hosting gas reservoirs at least as large as those of galaxies at the cosmic noon.

Dr Cortese said: “What we found is that despite hosting 10 billion solar masses of molecular gas these young galaxies turn out to be very, very rich in atomic hydrogen as well. The balance between atomic and molecular hydrogen is pretty much the same as in the Milky Way. In other words, it’s still dominated by atomic gas.”

The researchers used data from the Arecibo Observatory in Puerto Rico and the European Southern Observatory’s Atacama Large Millimeter/submillimeter Array in Chile. The paper was published in Astrophysical Journal Letters.