Most precise snapshot of the universe unveiled

From a palace in Ferrara, Italy, cosmologists have unveiled the most detailed maps yet of the infant universe. The announcement, on December 1, kicked off a weeklong conference showcasing the latest findings from the European Space Agency’s Planck satellite. The new results largely confirm earlier measurements of the makeup of the cosmos, but they also rule out some ideas about dark matter, the elusive substance thought to bind galaxies together.

There are no major surprises, says David Spergel, a cosmologist at Princeton University who, like most researchers, is relying on e-mail and Twitter to hear about the results. Compared with Planck’s first results, presented in 2013, not much has changed (SN: 4/20/13, p. 5). We live in a 13.8 billion-year-old universe where atoms and their subatomic components account for only 4.9 percent of all the mass and energy that’s out there. Dark matter makes up 26.6 percent, and 68.5 percent resides in the even more enigmatic dark energy, a repulsive force that is speeding up the expansion of the cosmos.

Planck’s value for the Hubble constant — which quantifies the current rate of cosmic expansion — holds steady in the new results at 67.3 kilometers per second per megaparsec. This value was previously at odds with a slightly higher number obtained through observations of supernovas (SN: 4/5/14, p. 18). A recent reanalysis of the supernova data, however, brings the two closer together.

Planck spent more than four years gathering light from the cosmic microwave background, the first light released into the universe, about 380,000 years after the Big Bang. The previously released results relied solely on measurements taken in Planck’s first year or so, which were of subtle differences in the intensity of that light coming from different points on the sky. Those variations map density fluctuations in the early universe, which in turn can be used to calculate the fundamental numbers, such as the Hubble constant, that describe the cosmos.

This week’s results incorporate not only fluctuation data taken in subsequent years but also polarization maps, which trace how the microwave light waves align with one another. The additional data allow researchers to home in on the most precise measurements of cosmological components to date.

“We’re squeezing” the data, says astrophysicist Joanna Dunkley of the University of Oxford, a member of the Planck team. Whereas Planck’s previous value for the relative amount of dark energy in the universe was good to within about 2 percent, she says, the new analysis tightens the uncertainty to just 1 percent. Dunkley also emphasizes that these results are preliminary. The team plans to publish a set of papers on December 22 and then publicly release all the data.

Planck may be able to rule out some theories about the nature of dark matter, which continues to evade direct detection. Recently the Fermi and PAMELA satellites, along with the Alpha Magnetic Spectrometer experiment onboard the International Space Station, have reported an abundance of positrons coming from deep space (SN: 5/4/13, p. 14). Many researchers attribute the high signals to collisions between dark matter particles.

But those collisions should have left a mark in the microwave background, a signal which Planck doesn’t see. That doesn’t rule out the existence of dark matter, or that it can create showers of subatomic particles. Instead it favors high-mass particles as dark matter candidates.

There’s no word yet on the alleged detection of primordial gravitational waves — ripples in the fabric of space injected into the universe in the first moments following the Big Bang — announced by the BICEP2 project earlier this year (SN: 4/5/14, p. 6). Other Planck results published in September did not support BICEP2’s report (SN: 10/18/14, p. 7), but the teams have since combined forces to jointly analyze data from both experiments. Those findings, originally planned for release in November, will probably be announced in several weeks.

In the meantime, mission scientists will keep wrestling with the data. This is not the last word from Planck, says Raphael Flauger, a cosmologist at Carnegie Mellon University in Pittsburgh, who is not involved with the mission. “It’s more of preview of what’s to come.” While the conference was intended to showcase the satellite’s latest insight into the universe, the complex analysis has taken longer than researchers had hoped. “I’ll be excited to see what happens a few weeks from now,” he says, when the data are finally published.

Editor’s Note: This article was updated December 8, 2014 to correct the length of time Planck spent gathering data.