Cosmic Fog Helps Astrophysicists Clock Just How Fast The Universe Is Expanding

At the cosmic level, dark energy is largely fueling the expansion of the universe, the rate of which is referred to as the Hubble Constant. The estimation of this rate first came from Ewdin Hubble, the astronomer after whom the Hubble Space Telescope was named. In the decades since, experts have been refining the estimate and the most recent work among that effort comes from a team of scientists led by the University of Clemson.

The original Hubble Constant estimated that the universe is expanding by 500 kilometers (310 miles) per second per megaparsec — that is, per 3.26 million light-years or thereabouts. Work to 'recalibrate' this estimate has taken place in the years since, though the Clemson researchers note that it has produced 'mixed results.'

A newly published study details the work that was put into coming up with a narrower estimate of 67.5 kilometers (42 miles) per megaparsec. The research involved data from multiple telescopes on gamma-ray attenuation and models on extragalactic background light, which is described as a sort of 'cosmic fog.'

The study's lead author Alberto Dominguez explained:

Our technique allows us to use an independent strategy – a new methodology independent of existing ones – to measure crucial properties of the universe ... The analysis that we have developed paves the way for better measurements in the future using the Cherenkov Telescope Array, which is still in development and will be the most ambitious array of ground-based high-energy telescopes ever.

The universe's expansion is compared to that of a balloon that expands as it is inflated — if two dots are drawn on the balloon, they move farther apart as it grows in size. In the case of the universe, the expansion is believed to be driven by dark energy and dark matter, which makes up the majority of the universe.