Washington

The first data from the Wilkinson Microwave Anisotropy Probe (WMAP) were released last week, some eight years after the mission was first proposed to NASA. The analysis of the data, by contrast, is happening much faster — it is already appearing on preprint servers.

The WMAP probe's images of cosmic microwaves (above) are set to be bettered by the Planck satellite (right). Credit: WMAP SCIENCE TEAM; INSET, ESA

The satellite, which has now spent more than a year surveying the sky at a distance of some 1.5 million kilometres from Earth, measures variations in the temperature and polarization of the cosmic microwave background (CMB), the faint radiation dating from the dawn of the Universe.

In an analysis done before the data were released, the WMAP team produced the best estimates yet of key cosmological parameters.

The new data imply an age for the Universe of 13.7 billion years, and a distribution of mass and energy in which 4% of the Universe is normal matter (atoms), 23% is dark matter, and 73% is dark energy. These figures fit well with previous estimates. The age at which the first stars seem to have formed — 200 million years after the Big Bang — is significantly earlier than most astronomers had thought.

“The really huge impact is that they tightened all the screws and bolts, and hammered everything with a superb precision,” says Max Tegmark, a cosmologist at the University of Pennsylvania in Philadelphia. As a result, he says, cosmology has taken “a giant leap forward in credibility”, and “has been transformed into a real hard science”.

Soon after the data were released on 11 February, papers began appearing on the arXiv preprint server operated by Cornell University. A group led by Carlos Martins of the University of Cambridge used the WMAP data to investigate the value of fundamental constants in the early Universe. Others compared the data to previous sky surveys and assessed its impact on theories of the geometry of the Universe. “I predict that you'll see a thousand other papers in the coming years,” says Tegmark.

The next big step in all-sky CMB mapping will be the European Space Agency's Planck satellite, due to launch in 2007. Planck will have three times the resolution of WMAP, and it should do a more thorough job of characterizing the foreground radiation, which can mask the faint signal from the microwave background.

Before then, several ground-based studies will examine small patches of the sky with even greater resolution. Among these are the South Pole Telescope, led by the University of Chicago, and the Chilean-based Atacama Pathfinder Experiment, proposed by the Max Planck Institute for Radioastronomy in Bonn. Their images of the microwave background may yield new information on the period when the first stars formed.

Another goal for future investigations is a more precise measurement of the polarization of the microwave background, discovered last year by the Degree Angular Scale Interferometer in Antarctica. The WMAP also measured this polarization, and a host of ground- and balloon-based instruments will take the investigation a step further.

One such balloon-based experiment, called BOOMERANG, recently completed a flight in Antarctica, where it collected “beautiful data” on the polarization with greater sensitivity than WMAP, according to principal investigator Andrew Lange of the California Institute of Technology. He expects to publish the results later this year.

→ http://arxiv.org