Physicists at the Leiden Institute in the Netherlands have found a way to determine the exact rate of expansion of the Universe in order to resolve the contradiction between the two methods, which gave different results. A mysterious discrepancy between the results made some scientists talk about the development of a crisis in cosmology. This is reported in an article published in the Monthly Notices of the Royal Astronomical Society, briefly about scientific work explained in a press release on Phys.org.
The researchers used a phenomenon called gravitational lensing, where a massive object like a galaxy (giving rise to a lens) bends light coming from a more distant background object like a quasar. In some cases, the gravitational lens is off-center, and as a result, some of the light rays will travel longer than others. The difference can be days, weeks or months. Thus, if a quasar changes its brightness, then a double image appears, with one part of it dimmer and the other brighter.
This time difference can be used to determine the distance to the lens and to the quasar itself. And if you compare the result with redshift, you can get an independent estimate of the Hubble constant. The researchers studied six quasars and found a value equal, on average, to about 73 kilometers per second per megaparsec. However, the error in this case remains high.
In a new work, scientists have proposed observing a thousand binary quasars using the Vera Rubin Observatory telescope, which will begin operating in 2021. Researchers have developed a method for calculating the mean effect that will give an accurate value for the Hubble constant with an error of only two percent.
According to the data obtained by the Planck Space Observatory when measuring the cosmic microwave background (this method allows us to trace the evolution of the Universe after the Big Bang), the value of the constant was 67.31 kilometers per second per megaparsec. At the same time, other methods indicate a different value for the Hubble constant – from 73.3 to 76.5 kilometers per second per megaparsec.