Latest results from cosmic microwave background measurements

The BICEP3 telescope is located at the Amundsen-Scott South Pole Station, Antarctica. The telescope is protected by the metal skirt that surrounds it. New data from BICEP3 and data from space missions, combined with older data, have helped improve previous limitations on the types of inflation models that could be used to describe the earliest moments in the universe. Credit: Harvard-Smithsonian Center for Astrophysics
The big bang was the moment that created the universe. It happened around 13.8 billion years ago. After matter (mostly hydrogen), had cooled sufficiently to allow neutral atoms formation, light was free to travel through space approximately 380,000 years later. The cosmic microwave background radiation (CMB) is that light that comes from the sky in uniform directions. Or so it seemed at first. Astronomers discovered over the past decades that radiation contains faint ripples and bumps at a brightness of just a part of one hundred thousand. This is the seeds for future structures like galaxies.

Astronomers have conjectured that these ripples also contain traces of an initial burst of expansionthe so-called inflationwhich swelled the new universe by thirty-three orders of magnitude in a mere ten-to-the-power-minus-33 seconds. The way cosmic ripples curl, which is due to gravitational waves during cosmic infancy, should hint at the existence of inflation. This effect could be as faint or even more subtle than the ripples.

It produces patterns in light called "B-mode Polarization", and is expected to be extremely faint. This daunting measurement is made even more difficult by other exotic processes in the universe. One of the most important is the faint glow from light particles in our galaxy aligned with magnetic fields. Magnetic fields can also be used to create B-mode patterns of polarization. This light is also polarized. Similar effects can be produced by radio waves coming from the galaxy. CfA astronomers at the South Pole discovered the first evidence of such curling six years ago. The signal was consistent with simple inflation models. However, subsequent measurements at different frequencies or colors of microwave light showed that the signal could be explained by galactic dust.

Astronomers have been meticulously observing the South Pole since the first B-mode polarization measurements. They have also added powerful data from telescopes operating at different frequencies to their observations. CfA astronomers D. Barkats, H. Boenish, J. Connors, J. Cornelison, M. Dierickx, M. Eiben, D.C. Goldfinger, P. Grimes, S. Harrison, K.S. Karkare, J. M. Kovac, B. Racine, S. Richter, B.L. Schmitt, T. St. Germaine, C. Verges, C.L. Wong, L. Zeng, and a large group of colleagues just completed an analysis all data from the South Pole experiment BICEP2, Keck Array and BICEP3 through 2018. They also compared the results to those from the CMB space missions Planck, and WMAP. Although data collection for these missions ended in 2013, and 2010, respectively, data processing continues. The scientists used the 2018 release. These new results improve on the best constraints on curling by approximately a factor two and provide powerful guidance on how models of inflation could be used to describe the earliest moments in the universe.

One broad class of simple models has been largely eliminated. According to the team, the best-known models of primordial gravitational waves are predicted by the South Pole's upgraded telescopes. These levels should be detected (or ruled off) in the next ten years. The team is currently upgrading the BICEP system. They expect to make another three significant improvements in five years. This will allow them to tighten constraints on inflationary models.

The research was published by Physical Review Letters.

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Additional information: P. A. R. Ade and co, Improved Constraints On Primordial Gravitational Waves Using Planck, WMAP, & BICEP/Keck Observations Through the 2018 Observing Season. Physical Review Letters (2021). Information from the Journal: Physical Review Letters P. A. R. Ade and co, Improved Constraints On Primordial Gravitational waves using Planck. WMAP and BICEP/Keck Observations Through The 2018 Observing Season (2021). DOI: 10.1103/PhysRevLett.127.151301