Cosmological anomaly confounds astronomers

An international team of researchers has uncovered a cosmological anomaly and are now trying to determine if it is an uncanny coincidence or a vital clue to understanding the origins of our Universe.

The irregularity, described in a paper accepted for publication in Astrophysical Journal Letters, has left the team, including researchers from Melbourne's Swinburne University of Technology, scratching their heads.

According to Swinburne co-author Dr Michael Murphy, the paper reveals a strange coincidence - or at least what appears to be a strange coincidence - occurring in distant galaxies.

"We were studying the abundance of molecules containing deuterium-deuterated molecular hydrogen (HD) in two different galaxies in the distant Universe.

"What we inadvertently discovered was that in these two galaxies the fraction of molecules which were HD was the same as the fraction of atoms which were deuterium (D), hydrogen's doubly-heavy cousin. We then looked at the only other two existing measurements of HD in distant galaxies and found almost exactly the same thing."

Dr Murphy said this was extremely unusual because HD should have a far more complex life cycle than D and researchers would expect it to be produced in very different amounts.

"Because deuterium was produced just after the Big Bang and never again, measures of its abundance are extremely important in telling us about cosmology. It is one of the few relatively precise probes of how many atoms there are in the Universe overall. Knowing this basic parameter is important if you want to know how the Universe began, the fate of the Universe and all of the steps in between," he said.

"But HD should be a completely different story," according to co-author Adrian Malec, a PhD student at Swinburne. "When we realised that the abundance of HD aligned with the abundance of D we were extremely surprised.

"It would appear that HD can be used to probe cosmology like D can. But this seems extremely far-fetched because of the complex life of HD molecules - how they're formed and how they're destroyed," he said.

"You would expect the abundance of HD to vary dramatically from place to place in the Universe. So if it is a coincidence, then it is a one in a million. Which means we now have to ask the question - is this is a bizarre coincidence or is it actually meaningful?"

According to Malec the finding raises more questions that now need to be answered. "We have four measurements of this molecule separated by very large distances, and in each case the abundance aligns with D," he said. "But we probably need a dozen more measurements before we can conclusively say whether this is a really strange coincidence or whether HD could potentially be used as a tracer for cosmology," he said.

The measurements were conducted using the world's largest optical telescopes at the Keck Observatory in Hawaii. Swinburne has an agreement with the California Institute of Technology (Caltech) that gives Swinburne astronomers access to the telescopes for up to 20 nights per year.