People use the phrase "Holy Cow" to express excitement. Playing with that phrase, researchers from an international collaboration developed an acronym—H0LiCOW—for their project's name that expresses the excitement over their Hubble Space Telescope measurements of the universe's expansion rate.

Knowing the precise value for how fast the universe expands is important for determining the age, size, and fate of the cosmos. Unraveling this mystery has been one of the greatest challenges in astrophysics in recent years.

Members of the H0LiCOW (H0 Lenses in COSMOGRAIL's Wellspring) team used Hubble and a technique that is completely independent of any previous method to measure the universe's expansion, a value called the Hubble constant.

This latest value represents the most precise measurement yet using the gravitational lensing method, where the gravity of a foreground galaxy acts like a giant magnifying lens, amplifying and distorting light from background objects. The study new not rely on the traditional "cosmic distance ladder" technique to measure accurate distances to galaxies by using various types of stars as "milepost markers." Instead, the researchers employed the exotic physics of gravitational lensing to calculate the universe's expansion rate.

The researchers' result further strengthens a troubling discrepancy between the expansion rate calculated from measurements of the local universe and the rate as predicted from background radiation in the early universe, a time before galaxies and stars even existed. The new study adds evidence to the idea that new theories may be needed to explain what scientists are finding.

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