Hubble astronomers check the prescription of a cosmic lens

[n2doc]

Two teams of astronomers using the NASA/ESA Hubble Space Telescope have discovered three distant exploding stars that have been magnified by the immense gravity of foreground galaxy clusters, which act like "cosmic lenses". These supernovae offer astronomers a powerful tool to check the prescription of these massive lenses.

Massive clusters of galaxies act as “gravitational lenses” because their powerful gravity bends light passing through them [1]. This lensing phenomenon makes faraway objects behind the clusters appear bigger and brighter — objects that might otherwise be too faint to see, even with the largest telescopes.

The new findings are the first steps towards the most precise prescription — or map — ever made for such a lens. How much a gravitationally lensed object is magnified depends on the amount of matter in a cluster — including dark matter, which we cannot see directly [2]. Astronomers develop maps that estimate the location and amount of dark matter lurking in a cluster. These maps are the lens prescriptions of a galaxy cluster and predict how distant objects behind a cluster will be magnified when their light passes through it. But how do astronomers know this prescription is accurate?

Now, two independent teams of astronomers from the Supernova Cosmology Project and the Cluster Lensing And Supernova survey with Hubble (CLASH) have found a new method to check the prescription of a gravitational lens. They analysed three supernovae — nicknamed Tiberius, Didius and Caracalla — which were each lensed by a different massive galaxy cluster — Abell 383, RXJ1532.9+3021 and MACS J1720.2+3536, respectively. Luckily, two and possibly all three of these supernovae appeared to be a special type of exploding star that can be used as a standard candle [3].

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http://www.spacetelescope.org/news/heic1409/