In a feat of cosmic observation, astronomers have used the distortions of ancient light left over from the Big Bang to explore how clumps of matter are distributed in the distant universe.
The work also independently confirms the existence of dark energy, an enigmatic force that appears to be pushing the cosmos apart faster and faster.
Researchers using the Atacama Cosmology Telescope in the Chilean Andes reported the discoveries July 5 in two papers in Physical Review Letters. The new work “will be a really powerful probe for figuring out dark energy and a lot of other interesting things,” says team member Blake Sherwin, a graduate student in astronomy at Princeton University.
Several scientists have won Nobel Prizes for studying the cosmic microwave background radiation, the afterglow left from the fireball that accompanied the creation of the universe 13.7 billion years ago. In the 2000s, a satellite called the Wilkinson Microwave Anisotropy Probe mapped how the radiation is spread across the entire sky. But seeing details like the distortions requires a telescope with more precise vision.
Using the 6-meter Atacama telescope, the astronomers analyzed the temperature of the afterglow in a narrow strip of sky along the celestial equator. They used complex statistical analyses to tease out how temperature fluctuations — essentially, hot and cold spots on the ancient sky map — had been distorted by intervening matter.
Astronomers regularly see such “gravitational lensing” with individual galaxies or galaxy clusters, when another massive clump of matter gets in the way. Just as a piece of broken glass distorts light passing through it, gravity from the foreground clump distorts the light coming from the more distant one, making it appear as a smeared-out arc.
Scientists first reported seeing gravitational lensing in the cosmic microwave background in 2007. Now the Atacama scientists have taken that work a step further: Their high-resolution data about gravitational distortions allowed them to extract more statistical information about how mass in the early universe is distributed. The new papers are also the first to discern the lensing without using other, outside sources of data.
“What’s nice about being able to detect lensing using just the cosmic microwave background is that you don’t have to make an assumption about knowing where the dark matter already is,” says team member Sudeep Das, a postdoctoral fellow at the University of California, Berkeley.
Using the new analyses, the Atacama team also verified that dark energy exists, as studies of distant exploded stars have suggested. “It’s arguably the most important measurement in physics in the last couple of decades, so it’s definitely worth confirming,” says Sherwin.
Together, the new studies open a window to studying where matter lies in the distant universe, says Wayne Hu, a cosmologist at the University of Chicago.
A different telescope may soon prop that window open even further. Astronomers working at the South Pole Telescope, a 10-meter behemoth in Antarctica, are expected to announce soon the results of a similar statistical analysis of gravitational lensing in the cosmic microwave background.
“This is the first time we’ve been able to get to this next step — to start mapping the mass distribution on the sky, which will be a very powerful probe of cosmology,” says John Carlstrom of the University of Chicago, leader of the South Pole team.
Other experiments will soon start hunting for lensing in polarized light coming from the Big Bang afterglow. When combined with data from the European Space Agency’s Planck satellite, cosmologists will have even more discoveries to chew over, says Das.
“There’s a lot to look for,” he says.
