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Black holes blamed for 'missing' hydrogen

Supermassive black hole

Supermassive black holes have enough power to ionise all the hydrogen in an entire galaxy (Source: NASA/JPL)

Ripped apart Supermassive black holes lurking in the heart of distant galaxies could be to blame for the 'missing' hydrogen in the early universe.

The discovery by Dr Stephen Curran of the University of Sydney and Dr Matthew Whiting of the CSIRO, explains why there doesn't appear to be enough hydrogen in the ancient universe to make all the stars we see today.

Their finding appears in the latest edition of the Astrophysical Journal.

Curran and Whiting were studying radio signals caused by monster black holes feeding in some of the earliest galaxies, 11 billion light years away.

"These are some of the oldest objects in the universe," says Curran.

Stars form from clouds of cold hydrogen at temperatures of just a few degrees above absolute zero (-273°C), collapsing through their own gravity.

"If you've got a galaxy then you've got hydrogen," says Curran.

"By studying these hydrogen signatures, we can determine the size and rotation of galaxies."

But some of the galaxies Curran and Whiting looked at appeared to contain less hydrogen than expected.

"We looked at ten ancient galaxies and were surprised to find no signs of hydrogen in any," says Curran.

"There should have been more cold hydrogen gas in these ancient distant galaxies than there is today."

A pattern emerges

As Curran and Whiting looked at other galaxy surveys, they found a critical level beyond which cold hydrogen could not be detected.

They found that in galaxies of certain luminosity, extreme levels of ultra-violet radiation given off by the supermassive black hole at its cores, generates enough energy to ionise all the hydrogen gas.

This ionised hydrogen can't be detected by radio telescopes.

"We didn't know all the gas in the galaxy was being ionised. We thought it was just around the black hole's accretion disk," says Curran.

"But it's the lot; ripping all the hydrogen into protons and electrons, preventing us from detecting it."

According to Curran, the Square Kilometre Array (SKA) radio telescope to be built in Australia, New Zealand and South Africa will provide a boost for their research.

"Not even the SKA can detect the hot ionised hydrogen in these active galaxies," says Curran.

"But it will let us look for other galaxies in the early universe which do have the cold hydrogen gas we're seeking."

Tags: blackholes, the-universe, physics, galaxies