Australasian Science: Australia's authority on science since 1938

Galaxy Caught Feeding

By Stephen Luntz

New insight into galactic formation in the early universe has been gained from the discovery of a galaxy whose fortunate positioning allows the observation of infalling gas.

A/Prof Michael Murphy of Swinburne University was part of an international collaboration that found a galaxy 11 billion light years away whose orientation enables measurements of the speed of gas circling its core. The galaxy is also lit up by the fortuitous presence of a quasar directly behind.

While the red shift of the gas indicates that some is orbiting at the same rate as the galaxy’s stars, Murphy says that other gas is moving at a different rate, consistent with what we would expect of slower objects entering the galaxy’s whirlpool.

“Star formation consumes gas very quickly,” says Murphy. “We can measure how quickly stars are formed, so we know that galaxies don’t contain enough gas to sustain themselves for long and must be drawing some in.”

While we have been able to observe this process in nearby galaxies, Murphy points out: “Star formation was much more prevalent in the early universe, so there must have been much more gas being sucked in”. There are competing theories of how this occurred, and the galaxies at a much earlier stage of their development are usually too far away to observe clearly.

The gas in this case is cold and dense, which is consistent with theories that it arrives in thick filaments rather than settling diffusely from all directions.

The galaxy in question is known as a starburst galaxy for its huge rate of star formation – 30 times that of the Milky Way. “It’s like feeding time for lions at the zoo,” says Murphy. “This particular galaxy has a voracious appetite, and we have discovered how it feeds itself to grow so quickly.”

The rapid growth results from a combination of sufficient mass to attract large amounts of gas, and the density of nearby gas on which it can draw. Murphy says smaller galaxies may feed in a subtly different manner.