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This is a colour-composite of the barred spiral galaxy NGC 5584. It is based on data collected by the Paranal Science Team with the FORS1 instrument on Kueyen, the second 8.2-meter Unit Telescope of ESO's Very Large Telescope. The Type Ia supernova SN 2007af is the bright object seen slightly below and to the right of the galaxy's centre. Astronomers use Cepheid variables and Type Ia supernovae as reliable distance markers to measure the universe's expansion rate and NGC 5584 was one of eight galaxies astronomers studied to measure the universe's expansion rate. In those galaxies, astronomers analyzed more than 600 Cepheid variables, including 250 in NGC 5584. Astronomers search for Type Ia supernovae in nearby galaxies containing Cepheid variables so they can compare true brightness of both types of stars. They then use that information to calibrate the measurement of Type Ia supernovae in far-flung galaxies and calculate their distance from Earth. Once astronomers know accurate distances to galaxies near and far, they can determine the universe's expansion rate.
NGC 5584 and its bright supernova were observed on the nights of 16, 19 and 22 March 2007 through a B, V, R, H-alpha and OII filter. The total exposure time is about 28 minutes. The observers are Susana Randall, Claudio Melo and Swetlana Hubrig, and the day astronomer was Dominique Naef (all ESO). Henri Boffin (ESO) processed the data and made the colour-composite, and Haennes Heyer (ESO) made the final adjustments.
Credit: ESO
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