The most detailed map ever made of the afterglow of the big bang – the primordial release of energy that gave rise to the visible universe some 13.8 billion years ago – has been unveiled.
The afterglow, a cosmic Rosetta Stone, provides a wealth of information on conditions in the early universe and its composition. And it reveals the seeds of structure that would eventually grow into the galaxies, clusters, and vast sheets and filaments of galaxies that populate the universe astronomers see today.
The data, unveiled Thursday, show a universe with slightly more matter and less "dark energy" than previously estimated, a slightly older universe, and one expanding more slowly than previously measured.
In key ways, the new map is providing a remarkable confirmation of the story cosmologists have compiled on how the universe came to be. But it's also displaying features that researchers are having a hard time explaining.
The inexplicable features could be the cosmological equivalent of an optical illusion, resulting from gravity's effect on the path of the afterglow's photons as they travel through space. Or the features could be embedded in the afterglow itself.
"Either possibility is fascinating," says Scott Dodelson, an astrophysicist at the Fermi National Accelerator Laboratory in Batavia, Ill.
But if the features truly are embedded in the afterglow, "that would be really important," he says, adding that it would lead to a better understanding of the processes that drove the early, exponential expansion of the universe.
For a fleeting moment some 10 nano nano nano nanoseconds after the big bang, the universe inflated at a stunning pace. In that fleeting moment, the cosmos expanded by 100 trillion trillion times, says Charles Lawrence, a researcher at NASA's Jet Propulsion Laboratory and the US project scientist for Planck, the European Space Agency space telescope that made the measurements.
As early as 1946, theorists predicted that the big bang would leave a relic afterglow. But researchers didn't deem it detectable until 1964 – about the same time two Bell Laboratory engineers were testing an exquisitely sensitive microwave antenna for telecommunications work.
The two unwittingly stumbled across the afterglow, formally known as the cosmic microwave background. They saw it as nuisance noise that wouldn't go away, no matter where in the sky the duo aimed the antenna. Cosmologists got wind of the measurements and checked them against theory. The results put the two engineers, Anro Penzias and Robert Wilson, on the fast track to Stockholm and a Nobel Prize in physics.
Planck is the third space telescope sent into orbit in the past 34 years to measure the cosmic microwave background.
The microwave radiation started out as white-hot light permeating a smaller, toastier universe made of a roiling soup of protons, photons, and electrons, cosmologists say. At the time, the universe was about 380,000 years old with temperatures of around 4,900 degrees Fahrenheit.
As the universe expanded and cooled, so did the radiation that traveled with it, until it dropped to microwave wavelengths and nosedived to about 2.7 degrees above absolute zero. The information cosmologists seek is recorded in subtle variations in temperature across the microwave sky on large and on small scales. Subtle is an understatement. Researchers are mapping variations on the order of 100 millionths of a degree.
Compared with its predecessors, Planck has an unmatched sensitivity to these changes and an ability to distinguish them across much smaller patches of sky. It is revealing the richest vein of information in the afterglow that cosmologists have ever seen.
"The latest results from Planck are breathtaking," writes Anais Rassat, an astrophysicist at the Swiss Federal Institute of Technology in Lausanne, in an e-mail.
The results show that the universe is a little older than previous estimates – 13.82 billion years old instead of 13.7 billion. Its composition has shifted a bit. Normal matter, which makes up stars, planets, and plants, is slightly more abundant than previous estimates. It makes up 4.9 percent of the matter and energy in the universe, rather than 4.3 percent. Dark matter, unseen but detected through its gravitational effects, is slightly more abundant – up from 22.7 percent to 26.8 percent of matter and energy. Dark energy, which is speeding the expansion of the universe, makes up 68.3 percent of the cosmos's matter and energy, down from 72.8 percent.
These may seem like trivial adjustments, but they are not, says Martin White, an astrophysicist at the University of California at Berkeley and a member of the Planck science team.
"For the working cosmologist, a number of these shifts are significant enough that I feel as though an awful lot of people will be doing calculations and rerunning their computer simulations with the new numbers," he says. "These are not irrelevant shifts. These are quite important."
But the oddities in Planck's map may turn out to muddy the picture – something scientists would eagerly embrace because if those oddities are embedded in the afterglow, "it could turn out to be a signature of exotic early-universe physics," Dr. Rassat says.
One such oddity appears as an unusually large cold spot in one hemisphere. Another shows up as a one hemisphere on the map being colder on average than the other. The warmer hemisphere seems to have the region of relative warmth aligned with the boundary between the hemispheres.
Some theories have predicted that the fluctuations in the microwave background should be randomly distributed across the sky – in effect expressing no preferred direction. The notion of a lack of preferred direction in the universe, which appears to hold for observations over a range of spatial scales, is a cornerstone of cosmology.
So when the odd features cropped up in data from earlier missions, scientists took note. But it was unclear if the effects were imposed by the instruments used to make the measurements or whether the features were indeed from outer space. Between Planck and NASA's earlier WMAP microwave observatory, it's clear the features are in space and not in hardware, researchers say.
Members of the Planck team express confidence that the unexpected features they see are embedded in the afterglow itself.
Others argue that those features could yet be illusions. Gravity from large galaxy clusters or sheets of galaxies could have altered the path of photons as they traveled, making it look as though some regions of the cosmic microwave background were denser and hotter than others.
It could take time to sort out with confidence whether the oddities are real or illusions, suggests Fermilab's Dr. Dodelson. Data from new sky-survey programs should help. These surveys are designed in part to hunt for ever more-distant galaxies in the universe. As the data roll in, researchers will be able to get a better estimate the mass of the matter along the line of sight to these features, refine their estimates of the gravitational effect the mass has on passing photons, and calculate its contribution to the unusual features they see.