Approximately ten billion years ago when the universe was one-fifth its current age, early proto-galaxies were in a state of extreme activity, forming new stars nearly one hundred times their current rate. Because stars form from gas, this fecundity demands a steady source of cosmic fuel.
In the past decade, supercomputer simulations of galaxy formation have become so sophisticated that they can actually predict how galaxies form and are fed: gas funnels onto galaxies along thin "cold streams" which, like streams of snow melt feeding a mountain lake, channel cool gas from the surrounding intergalactic medium onto galaxies, continuously topping up their supplies of raw material for star formation.
However, testing these predictions has proven to be extremely challenging, because such gas at the edges of galaxies is so rarefied that it emits very little light. Instead, the team of astronomers systematically searched for examples of a very specific type of cosmic coincidence.
Quasars constitute a brief phase in the galactic life-cycle, during which they shine as the most luminous objects in the universe, powered by the infall of matter onto a supermassive black hole.
As light from the quasar travels toward Earth, it passes by the galaxy and through the primordial gas, before reaching our telescopes.
The cosmic gas selectively absorbs light at very specific frequencies which astronomers refer to as "absorption lines." The pattern and shape of these lines provide a cosmic barcode, which astronomers can decode to determine the chemical composition, density, and temperature of the gas.
Using this technique, a team of astronomers led by Neil Crighton (Max Planck Institute for Astronomy; now at Swinburne University of Technology, Melbourne) has found the best evidence to date for a flow of pristine intergalactic gas onto a galaxy, denoted Q1442-MD50.
The results have been published in the Astrophysical Journal Letters.
--ANI (Posted on 03-10-2013)