United in the collaborative project H0LiCOW (acronym for H0 Lenses in COSMOGRAIL’s Wellspring ), a group of astronomers has set out to establish as accurately as possible the Hubble constant call , fundamental to understanding how the cosmos works. This value measures the speed at which galaxies are moving away from each other and, until now, it was fixed at 71 kilometers per second and megaparsec, taking into account that a megaparsec is three million light years.
But the H0LiCOW measurements, based on the collection of data from different telescopes located on Earth and in space – including the Hubble space observatory – indicate that the expansion speed of the universe can be up to 9% faster than what they establish the cosmological models . The same discrepancy was already revealed by another independent investigation made public last summer, which compared the brightness of Cepheid stars – which change their luminosity at regular intervals – and type IA supernovae.
As the researchers explain in a series of articles published in the Monthly Notices of the Royal Astronomical Society magazine, in the case of the H0LiCOW project, an attempt was made to establish the value of the Hubble constant with two different techniques. First, the records of the Planck satellite were analyzed, which measures the microwave background radiation , that is, the faint echo of the Big Bang that permeates the entire universe. and the results conformed to the standard cosmological model. In other words, up to here, everything is correct.
The problem arose with the second measurement, which took advantage of a phenomenon called “gravitational lensing”, discovered in 1979 . This occurs when the galactic clusters behave like a kind of magnifying glass and allow us to see very distant objects.
The H0LiCOW scientists specifically focused on pulsars, supermassive neutron stars that emit regular pulses of radiation and whose image is multiplied by gravitational lenses. It is with the subtle difference in brightness between those repeated mirror images that they made the new value of the constant, theoretically more exact .
“The expansion rate of the cosmos is beginning to be measured with such precision that the differences may point to a new physics beyond our current knowledge of the universe, ” explained Sherry Suyu, researcher at the Max Plancks Institute for Astrophysics and director of the project. H0LiCOW.
Photo: Quasar image through a gravitational lens (center). Credit: Esa / Hubble / Nasa / Suyu
