English: The heart of a vast cluster of galaxies called MACS J1720+35 is shown in this image, taken in visible and near-infrared light by NASA's Hubble Space Telescope.

The galaxy cluster is so massive that its gravity distorts, brightens, and magnifies light from more-distant objects behind it, an effect called gravitational lensing. The small white box at upper right marks the location of an exploding star called a supernova, located behind the cluster.

An enlarged view of the supernova, catalogued as SCP/SN-L2, is shown in the inset image at top right, taken during July 2012. An arrow marks the location of the supernova, which resides near the bright core of the host galaxy. The supernova is seen as it appeared 7.7 billion years ago. The image was taken in near-infrared light with Hubble's Wide Field Camera 3.

The inset image at top left, taken in March 2012, shows the same region before the supernova blast. This image underscores the transient nature of exploding stars. Astronomers combined observations taken in visible and near-infrared light with Hubble's Advanced Camera for Surveys and Wide Field Camera 3 to make the image. The supernova is a member of a special class of exploding star called Type Ia, prized by astronomers because it provides a consistent level of peak brightness that makes it reliable for making distance estimates.

Finding a gravitationally lensed Type Ia supernova gives astronomers a unique opportunity to check the optical "prescription" of the foreground lensing cluster. The supernova is one of three exploding stars discovered in the Cluster Lensing And Supernova survey with Hubble (CLASH), and was followed up as part of a Supernova Cosmology Project HST program. CLASH is a Hubble census that probed the distribution of dark matter in 25 galaxy clusters. Dark matter cannot be seen directly but is believed to make up most of the universe's matter.

The image of the galaxy cluster was taken between March and June 2012 by Hubble's Wide Field Camera 3 and Advanced Camera for Surveys.