The universe was created about 13.8 billion years ago in the light: the big bang. About 380,000 years later, after matter (mostly hydrogen) had cooled enough for neutral atoms to form, light could freely cross space. That light, the cosmic microwave background radiation (CMB), comes uniformly from all directions in the sky … or so it seemed at first. In recent decades, astronomers have discovered that the radiation has faint ripples and bulges in it at a brightness level of only a fraction of a hundred thousand – the seeds for future structures, such as galaxies.
Astronomers have assumed that these ripples also contain traces of an initial expansion eruption — the so-called inflation — that swelled the new universe by thirty-three orders of magnitude in just ten-to-power-minus-33 seconds. Clues about inflation should be weakly present in the way the cosmic ripples curl, an effect due to gravitational waves in cosmic childhood that are expected to be perhaps a hundred times or more weaker than the ripples themselves.
The curling effect produces patterns in the light known as “B-mode polarization”, and it is expected to be extremely weak. Other exotic processes are working in the universe to make this scary measurement even more challenging. The most important is the faint light of light from dust particles in our galaxy, which has been adjusted by magnetic fields. This light is also polarized and can be twisted by magnetic fields to produce B-mode polarization patterns. Radio waves from our galaxy can produce similar effects. About six years ago, CfA astronomers working at the South Pole reported the first evidence of such curling, “B-mode polarization,” at levels consistent with simple inflation models but subsequent measurements at different frequencies (or colors). ) of microwave light revealed the signal must be explained with galactic dust.
In the years since the first measurements of B-mode polarization, astronomers have continued their careful observations and added powerful data from new telescopes at many different frequencies operating at the South Pole. CfA astronomer D. Barkats, H. Boenish, J. Connors, J. Cornelison, M. Dierickx, M. Eiben, DC Goldfinger, P. Grimes, S. Harrison, KS Karkare, JM Kovac, B. Racine, S. Richter, BL Schmitt, T. St. Germaine, C. Verges, CL Wong, L. Zeng and a large team of colleagues have just completed an analysis of all data from the South Pole experiments BICEP2, Keck Array and BICEP3 through 2018, and correlate the results with results from the CMB space missions Planck and WMAP. (Although data collection for these missions ended in 2013 and 2010, respectively, data processing continues, and researchers used the 2018 release.) that could describe the earliest moments of the universe.
A wide class of simple models is now largely ruled out. The team reports that the most favored of the remaining class of models predict initial gravitational waves at levels that should be detected (or ruled out) within the next decade with upgraded telescopes at the South Pole. The team is already in the process of upgrading the BICEP system and expects to get another factor of around three improvements within five years, enough to set tight limits for inflation models.
The study was published in Physical review letters.
Cosmologically complicated dust
PAR Ade et al., Improved limitations on primordial gravitational waves using Planck, WMAP, and BICEP / Keck observations throughout the 2018 observation season, Physical review letters (2021). DOI: 10.1103 / PhysRevLett.127.151301
Provided by the Harvard-Smithsonian Center for Astrophysics
Citation: Latest results from cosmic microwave background measurements (2021, October 8) retrieved October 8, 2021 from https://phys.org/news/2021-10-latest-results-cosmic-microwave-background.html
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