By Geoff Brumfiel

A spacecraft designed to study the faint afterglow of the Big Bang has discovered a rash of new galaxy clusters, along with details of our own Milky Way.

Orbiting the Sun roughly 1.5 million kilometres from Earth, the Planck space-based telescope is scanning the sky for ultra-cold objects. Its instruments are chilled to just a tenth of a degree above absolute zero and are designed to pick up the faint microwave afterglow from the Big Bang, which scientists hope can tell them about the earliest moments of the Universe (see 'The test of inflation').

But the telescope, operated by the European Space Agency, also picks up other things. In a press conference today in Paris, members of the Planck mission announced that it had detected some 15,000 sources of microwaves across the entire night sky.

"For the Planck community, this is a big day," says Jan Tauber, Planck's chief project scientist, based at the European Space Research and Technology Centre in Noordwijk, the Netherlands. "This catalogue we are releasing is really a treasure trove."

Galactic cobwebs

Among the microwave sources detected are 30 previously undiscovered galaxy clusters, clumps of galaxies that can measure 3 million parsecs across. The clusters sit at the intersections of vast 'cobwebs' of galaxies spreading across the Universe. Some researchers want to compare the spacing between clusters in the early Universe to those of modern clusters. Differences could reveal more about dark energy, a mysterious force that appears to be pushing the cosmos apart.

The mission has also picked up what researchers believe to be light from some of the earliest galaxies in the Universe. The ubiquitous infrared glow covers much of the sky and seems to be emanating from galaxies that form 10-1,000 new stars a year. By contrast, the Milky Way forms just one new star a year.

Closer to home, the spacecraft has apparently nailed the source of a microwave fog that covers much of the Milky Way. Researchers have known about the fog for decades, but only now can they say with confidence that it is coming from dust grains spinning rapidly in interstellar space. Their speedy spin causes their electrons to emit a faint glow, seen clearly by Planck's instruments.

Tracking inflation

All this is a prelude to the mission's main goal: charting the cosmic microwave background (CMB), which dates from just 380,000 years after the Big Bang, roughly 13.7 billion years ago. Measuring the CMB with unprecedented sensitivity will allow Planck to learn details of a period that cosmologists call inflation, in which the Universe expanded extremely rapidly. Inflation helps to explain the distribution of matter in the Universe, but nobody knows how it began, or why it ended. Planck's measurements could shed light on the origins and mechanism of the inflationary period.

Scientists will operate the Planck telescope until the end of the year and hope to complete their map of the microwave background by January 2013.From the perspective of the CMB, these newly announced discoveries are actually noise. Scientists will have to eliminate these microwave sources and many others before they can reconstruct an unpolluted map of the CMB. "It's a really juicy first taste of what's to come," says Tauber.