Something vital is missing in the far distant reaches of the Universe: hydrogen - the raw material for stars, planets and possible life.
The discovery of its apparent absence from distant galaxies by a teamof Australian astronomers is puzzling because hydrogen gas is the mostcommon constituent of normal matter in the Universe.
If anything, hydrogen was expected to be more abundant so early in thelife of the Universe because it had not yet been consumed by theformation of all the stars and galaxies we know today.
Dr Steve Curran and colleagues at the University of New South Walesmade their observations with the Giant Metrewave Radio Telescope inIndia, which comprises thirty 45-metre-diameter dishes and is one ofthe world's most sensitive radio telescopes. The results are to bepublished in a forthcoming issue of Monthly Notices of the RoyalAstronomical Society.
By looking at galaxies in which the light has taken over 11.5 billionyears to reach us, they found an apparent lack of hydrogen when theUniverse was only two billion years old - long before our own Sun andall other stars in the present Universe had formed.
Stars form when extremely cold clouds of hydrogen collapse under theirown gravity until they become dense enough to ignite nuclear fusion.Over billions of years, this leads the formation of the heavierelements that make up planets, people and other matter. Each galaxyshould contain gas masses equivalent to several billion stars, as inthe Milky Way.
"Since hydrogen gas is consumed by star formation, we may expect morehydrogen gas in the distant, and therefore earlier, Universe as all ofthe stars we see today have yet to form," Dr Curran says.
His group analysed the data from optical telescopes and found that,although apparently dim due to their immense distances, the distantgalaxies actually emit vast amounts of energy.
This energy is generally believed to result from the friction of thematerial spiralling at close to the speed of light into the black holelurking within the heart of each galaxy. These "quasars" are found allover the sky but occur predominantly in the early Universe.
"At such distances, only the most optically bright objects are known,"Dr Curran says. "The intense radiation from the matter accreting intothe black hole in these quasars is extreme and we believe that thisradiation is ripping the electrons from the atoms, destroying thehydrogen gas."
This would leave the gas as a soup of free subatomic particles knownas a "plasma", which cannot be detected at the radio frequenciessearched.
"Searching for neutral hydrogen in quasar host galaxies at suchdistances is really pushing current radio telescopes to their limits,"Dr Curran says. "With the next generation of instruments, such as theAustralian Square Kilometre Array Pathfinder, we may be able to probedeep enough to find just how ionised the gas is.
"Meanwhile, astronomers should search for sources of radio emissionthat have no optical counterpart. The emission tells us that somethinginvisible to an optical telescope is there. Such galaxies would hostmore benign quasars in which we may detect the neutral gas."
Source: University of New South Wales