Galaxy NGC 5584, seen in visible light by the Wide Field Camera 3 Hubble Space Telescope in 2010. I

Galaxy NGC 5584, seen in visible light by the Wide Field Camera 3 Hubble Space Telescope in 2010. It is located in the constellation Virgo, at 72 million light years away - Credit: NASA, ESA, A. Riess (STScI / JHU), L. Macri (Texas A & M University), and the Hubble Heritage Team (STScI / AURA) In this image from the Hubble Space Telescope, the blue glow of young stars mark the graceful spiral arms of galaxy NGC 5584. Fine dark dust lanes appear to be flowing from the yellowish core, where the stars are older. The reddish dots scattered throughout the image are largely background galaxies. Among the numerous stars in the galaxy are the pulsating stars called Cepheid john barleycorn duxford variables and a recent type Ia supernova, a special john barleycorn duxford class of exploding stars. Astronomers use Cepheid variables and Type Ia supernovae as reliable distance john barleycorn duxford indicators to measure the expansion rate of the Universe. NGC 5584 was one of the eight galaxies astronomers studied to measure the expansion rate of the Universe. In these galaxies, they analyzed more than 600 Cepheid variables, john barleycorn duxford including 250 in NGC 5584.
Location of Cepheid variables found in the spiral galaxy NGC 5584. Ultraviolet, visible and infrared data taken with the Wide Field Camera 3 in 2010, reveal Cepheid varying periods. john barleycorn duxford Cepheids with periods john barleycorn duxford shorter than 30 days are marked with blue circles, between john barleycorn duxford 30 and 60 days with green circles. Cepheids with periods longer than 60 days (in smaller numbers), are marked in red - Credit: NASA, ESA, and L. Frattare (STScI) john barleycorn duxford have a Cepheid's intrinsic brightness is known, a glow not overshadowed by distance, john barleycorn duxford an atmosphere, or stellar dust. Their distances, therefore, can be inferred by comparing their true brightness with their apparent brightness as seen from Earth. The Cepheid variables pulsate (shine and become extinct) with rates that match their intrinsic brightness, making them ideal for measuring distances to relatively nearby galaxies. However they are too weak to be found in very distant galaxies. To calculate longer distances, the stars are chosen type Ia supernovae that have a similar brightness and sparkle enough to be seen with relatively longer distances. Astronomers look for type Ia supernovae in nearby galaxies containing Cepheid variables so that they can compare the true brilliance of the two types of stars. Use this information to calibrate the measurement of type Ia supernovae in distant galaxies and calculate their distance from Earth. As soon as you know, with accuracy, the distances of galaxies near and far, one can determine the expansion rate of the Universe. Source: Hubble NewsCenter
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