Searching for Inflation (cont.)
Page 3/3 - Posted August 1, 2016
“We had detected B-mode polarization,” Kovac said. “It looked as though the most likely explanation was that in fact it was produced by gravitational waves from inflation.”
Photo Credit: Mike Lucibella
The BICEP3 receiver is the part of the collaboration that is tuned specifically to the polarized swirls of light left over from the early universe.
After the announcement, unexpected data started to come out about the strength of galactic dust that mimics these B-mode signals. The team had corrected for this based on what was known about the dust at the time, but new research was starting to emerge indicating that this dust might be a bigger problem than anticipated.
“What we subsequently found with data from the Planck satellite and now multi-frequency data from our own telescope… is that the dust in our galaxy produces more polarized emissions than had been previously thought,” Kovac said.
Ultimately, the dust turned out to be so bright that they couldn’t definitively separate out the signals from the early universe from the interfering dust. Undeterred, the team set about developing a way to sift through all of the noise and extract that weak signal from the louder interference.
“We know how to separate those signals out by continuing to take multi-frequency data that allows the separation,” Kovac said. “It just means that there’s more work involved in the interpretation.”
View previous Antarctic Sun articles about cosmic inflation research.
Now, observing this dust is a central part of the team’s approach.
“In order to tell [if] whatever signal we see is from the beginning of the universe, or from the galaxy, what you need to do is you need to look in ‘color.’ You need to look at different frequencies of microwave light. BICEP3 by virtue of being all in one receiver can only really look at one color at a time,” Karkare said. “What Keck Array can do here, is because it’s modular, we can change colors as individual receivers.”
The two telescopes are collecting complimentary data while pointed at the same patch of sky, a region known as the Southern Hole because there’s little galactic dust blocking the telescope’s view of the distant universe. BICEP3 is using its state of the art light detectors to observe microwave emissions at 95 gigahertz, the range where interference from galactic dust is the least. Nearby, the Keck Array is tuned to some of the frequencies where the glare from the galactic dust blots out everything else.
Photo Credit: Mike Lucibella
Together, the BICEP3 and Keck Array are working to detect signals from the ancient universe.
“We’re going to replace this [95 gigahertz detector array] with this 220 gigahertz one which is very sensitive to dust,” Karkare said as he worked on one of Keck’s receivers in December. “We’re not going to see CMB B-modes in here; we’re going to see dust B-modes in here.”
With a comprehensive map of all of the swirling polarization patterns in the sky, the team can meticulously subtract out the patterns that originated from the galactic dust from the CMB signals they’re looking for.
It’s a long, laborious process to collect all the data and process it. It’ll likely take at least a few seasons to finish scanning the skies using the two telescopes, then more time to fully disentangle the B-modes of the ancient universe from the ones produced by galactic dust. They’re not sure how soon they might be ready to announce their next results, but when they do, they’re confident that it’ll shed new insight onto the early evolution of our universe.
“The science over here [at BICEP3] and the science at Keck are blended together to produce results,” Ahmed said. “The combined power from all of this should get us some exciting results.”
NSF-funded research in this story: John Kovac, Harvard University, Award No. 1313287 . Chao-Lin Kuo, Stanford University, Award No. 1313010 . Clement Pryke, University of Minnesota-Twin Cities, Award No. 1313158 . James Brock, California Institute of Technology, Award No. 1313062 .