Dark energy

A measurement of the Hubble constant based on quasars suggests possible changes to cosmological models

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An article published in the journal “Nature Astronomy” describes the use of quasars as cosmic tracers to measure the expansion of the universe up to 12 billion years ago. Guido Risaliti of the University of Florence and Elisabeta Lusso of Durham University studied the X-ray and optical emissions of a number of quasars using the comparison between those emissions to accurately assess their distances. The results could explain the discrepancies between the different measurements carried out with other methods suggesting that the density of the mysterious dark energy isn’t constant over time.

Artist's concept of the universe on a 5D bubble (Image courtesy Suvendu Giri)

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An article published in the journal “Physical Review Letters” describes a new model of the universe that proposes that it exists on the edge of an expanding bubble in a five-dimension space-time. A team of researchers from the Swedish University of Uppsala used string theory to hypothesize that the matter existing in the universe is accomodated at the edges of strings that extend into the fifth dimension. According to this hypothesis, what is called dark energy is an effect described by a cosmological constant in the four-dimension Friedmann equations.

CMB Final Map (Image ESA/Planck Collaboration)

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ESA presented the final map of the cosmic microwave background radiation created thanks to the Planck Surveyor space probe. This map shows what the universe was like before galaxies formed when it was about 380,000 years old. These are the results of the last processing of the collected data and now scientists are certain that the temperature and polarization are accurately determined. This final map confirms the standard model but also the inconsistency between the calculation of the Hubble constant based on those data and the one based on observation of the current universe.

Scheme of Hubble and Gaia at work (Image NASA, ESA, and A. Feild (STScI))

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An article published in the journal “The Astrophysical Journal” describes a new measurement of the expansion of the universe. A team of astronomers led by Nobel Prize winner Adam Riess combined observations made with the Hubble Space Telescope and those made with ESA’s Gaia space probe, an observatory that specifically aims to map billions of objects in the sky including the variable stars called Cepheid variable used for those measurements. The new results increase the accuracy but also the discrepancy between the measures of the expansion of the near universe and those of the early universe.

Dark Energy Survey's map (Image Chihway Chang/Kavli Institute for Cosmological Physics at the University of Chicago/DES Collaboration)

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The Dark Energy Survey (DES) collaboration presented a map of dark matter at the American Physical Society Division of Particles and Fields at Fermilab created using gravitational lensing effects from 26 million galaxies. These results show the composition of the recent universe and are very close to the predictions based on the map created upon measurements the primeval universe of ESA’s Planck Surveyor satellite.