b'Carnegie Science|Fall 2019 11New Method to CalculateThis visualization is of the tip of the red giant Expansion Rate of the Universe branch of stars, showing the distribution of stars brightness versus their color. Image courtesy Meredith DurbinDimmer BrighterFrom afar two bells may well appearThe team used the Hubble Space to be the same; listening to their tones canTelescopes sensitive cameras to search reveal that one is actually much largerfor red giants in nearby galaxies.and more distant, and the other is smallerOnce the distances to these newly and closer, explained Carnegies Barryfound red giants are known, the Hubble Madore, a coauthor. Likewise, comparingConstant can be calculated with the help how bright distant Cepheids appear to beof another standard candle, Type la against the brightness of nearby Cepheidssupernovae, to diminish the uncertainty enables us to determine how far awaycaused by the red giants relative each of the stars host galaxies are. proximity to us and extend our reach out When a celestial objects distance isinto the more-distant Hubble flow.known, a measurement of the speed atBluer Redder According to the red giant method the which it is moving away from us revealsuniverses expansion rate is 69.8, falling the universes rate of expansion. The ratioprovocatively between the two previously of these two figures, the velocity dividedThe Carnegie-Chicago Hubbledetermined numbers.by the distance, is the Hubble Constant. Program, led by Freedman and includingWere like that old song, Stuck in the The second method uses theCarnegie astronomers Madore,Middle with You, joked Madore. Is there afterglow left over from the Big Bang.Christopher Burns, Mark Phillips, Jeffa crisis in cosmology? Wed hoped to beCalled cosmic background radiation, it isRich, and Mark Seibertas well asa tiebreaker, but for now the answer is:the oldest light we can see. Patterns ofCarnegie-Princeton fellow Rachaelnot so fast. The question of whether the compression in the thick, soupy plasmaBeatondeveloped a new way to calculatestandard model of the universe is complete from the baby universe can still be seenthe Hubble Constant. or not remains to be answered.and mapped as slight temperatureTheir technique is based on very variations. These ancient ripples can beluminous stars called red giants. During modeled forward in time and predict thethese stars life cycles, the helium ignites present-day Hubble Constant. and their structures are rearranged by this The former technique says thenew source of energy in their cores.expansion rate of the universe is 74.0The peak brightness of a red giant in kilometers per second per megaparsec;this state is easily differentiated, Madore the latter says its 67.4. If its real, theexplained. This makes them excellent discrepancy could herald new physics. standard candles.Enter the third option.SUPPORT:Support for this research was provided by NASA through aCoauthor Barry Madore hoped that the teams new grant from the Space Telescope Science Institute, operatedmethod for calculating the expansion rate of the by the Association of Universities for Research in Astronomy; the U.S. National Science Foundation; the National Researchuniverse, the Hubble Constant, would confirm the value Foundation of Korea, funded by the Korean Government;calculated by one of the other two competing methods. NASA through Hubble Fellowship; the Carnegie InstitutionBut their alternative value was in between the other two, for Science; and the University of Chicago. leaving the definitive value an open question. Computing resources used for this work were made possibleImage courtesy Carnegie Institution for Scienceby a grant from the Ahmanson Foundation. This research made use of the NASA/IPAC Extragalactic Database, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes.'