In a new study, a group of astronomers proposes a new way to determine the rate of expansion of our Universe – measuring the Hubble constant – which is based on an analysis conducted for images of distant bright galaxies with active supermassive black holes – quasars.
The Hubble constant is a number connecting the distance to the galaxy and its redshift – an indicator of how much the light moving from this galaxy in our direction, has undergone stretching as a result of passing through the expanding Universe. Estimates for the Hubble constant vary from about 67 to 73 kilometers per second per megaparsec.
The Hubble constant defines the physical scale of our universe.
-Simon Birrer, a postdoc researcher at the University of California at Los Angeles and principal author of the new work.
Without knowing the exact value of the Hubble constant, astronomers cannot accurately determine the size of distant galaxies, the age of the Universe, or the history of space expansion.
In his study, Birrer and his colleagues determined the Hubble constant using the original method, based on the fact that the light coming to us from distant quasars undergoes splitting under the influence of gravity of nearby galaxies, as a result of which we observe two images of the same quasar. . The light that forms each of the two images of the same quasar moves along different routes. Therefore, when a quasar flickers, this flicker is observed in two of its images with a delay, which, together with information about the gravitational field of the galaxy, lying in the foreground, allows you to calculate the distance to the quasar, and to this galaxy, acting as a gravitational lens. Knowledge of the redshifts of the quasar and the galaxy lens allowed astronomers to estimate the rate of expansion of the universe.
The value of the Hubble constant obtained by the Birrer team is 72.5 kilometers per second per megaparsec, which is consistent with an estimate of this constant obtained when determining the distances to supernovae, but diverges by almost 8 percent from an estimate based on the analysis of a dull sky glow called relict radiation . While scientists do not know exactly which of these two methods for determining the Hubble constant is correct, it is also possible that both approaches are correct, and the differences in the determination of this physical constant by various methods are related to the action of one or several unaccounted factors.
The snapshot of the quasar allowed for a new estimate of the Hubble constant
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