A new technique might soon enable cosmologists to map the universe even when they can’t pick out individual galaxies. If it works, researchers would be able to probe the structure of 500 times as much of the universe as they have studied so far.
* scientists have surveyed only 0.1% of the observable universe
* Instead of searching for the light from individual galaxies with an optical telescope, the team stalked a different quarry, red-shifted radio waves emitted by hydrogen atoms floating in huge clouds within the galaxies.
* Subtracting out radio signals 100,000 times stronger from our own galaxy and from television broadcasts, they detected the blurred 21-centimeter signals from galaxies about 6 billion to 12 billion light-years away.
* To be useful in mapping the universe, the method needs to be refined so that researchers need study only the variations in the 21-centimeter radiation alone. “We’re working on that right now,” Chang says. With a purpose-built radio telescope, the approach could map as much as 50% of the observable universe far faster and cheaper than galaxy surveys can
Chang and colleagues are developing plans for just such a radio telescope. Chang says it would cost about $20 million, a tiny fraction of the $2 billion radio astronomers want for the proposed Square Kilometre Array (SKA) of radio telescopes, which aims to trace large-scale structure by locating individual galaxies. If the new technique works, then in that regard “it does somewhat obviate the need for an SKA,” says Chris Carilli of the National Radio Astronomy Observatory in Socorro, New Mexico. But Chang is quick to point out that SKA has other objectives as well.