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Cosmic conundrum puzzles astronomers

Distant galaxies

Abundances of two very different types of hydrogen in certain galaxies have been found to be equal. Astronomers aren't sure why.

Researchers have 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 has left the team, including researchers from Melbourne’s Swinburne University of Technology, scratching their heads.

According to Swinburne scientist Dr Michael Murphy, the research reveals a strange coincidence—or at least what appears to be a strange coincidence—occurring in distant galaxies.

The astronomers were measuring the abundance of a type of hydrogen—called deuterium-deuterated molecular hydrogen, or HD for short—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,” says Dr Murphy.

Distant galaxies

More observations are planned of other galaxies

“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.”

A bizarre cosmic coincidence?

Measuring the abundance of deuterium is one of the few relatively precise ways of telling 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,” adds Dr Murphy.

“But HD should be a completely different story,” according to 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.

Keck Observatory

The astronomers used the huge Keck Observatory in Hawai'i

“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,” adds Malec.

“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 [HD] separated by very large distances, and in each case the abundance aligns with D,” he said.

The astronomers say they probably need a dozen more measurements before they can conclusively state whether this is a just strange coincidence or whether measurements of HD could potentially be used to help them understand the evolution of the universe.

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.

A paper describing the work has been accepted for publication in the journal Astrophysical Journal Letters.

Adapted from information issued by Swinburne University / STScI / Keck Observatory.

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