b'10 Carnegie Science|Fall 2019New Method to Calculate Expansion Rate of the UniverseA team of collaborators from Carnegie andThe Hubble Constant is the the University of Chicago used red giantcosmological parameter that sets the stars to make an entirely newabsolute scale, size, and age of the measurement of how fast the universe isuniverse; it is one of the most direct ways expanding, joining the hotly contestedwe have of quantifying how the universe debate. The Astrophysical Journal evolves, said lead author Wendypublished their result, which fallsFreedman of the University of Chicago, squarely between the two previous,who began this work at Carnegie.competing values. Until now, there have been two Nearly a century ago, Carnegieprimary tools used to measure the astronomer Edwin Hubble discovered thatuniverses rate of expansion. the universe has been growing since theUnfortunately, their results dont agree Big Bang. But precisely how fast itseven as each side makes increasingly expanding, a value termed the Hubbleprecise readings. It is possible, however, Constant, has remained elusive. that the difference between the two values The Hubble Constant helpedis due to systemic inaccuracies in one or scientists determine the universesboth, which spurred the research team to history and structure; an accuratedevelop the new technique.measurement of the Constant mightOne method, pioneered at Carnegie, Carnegie astronomer Edwin Hubble discovered thatreveal any flaws in the model.uses stars called Cepheids, which pulsate the universe has been expanding since the Big Bang.at regular intervals. Because the rate at But the rate of expansion, called the Hubble Constant, has remained elusive.which they pulse is related to their Image courtesy Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino,intrinsic brightness, astronomers use California their luminosities and the period between pulses to measure their distances from Earth.The team used Edwin Hubbles namesake telescope, the Hubble Space Telescope, to measure the expansion rate of the universe using Red Giant stars. Image courtesy NASA and the Space Telescope Science Institute (STScI)'