Single Hubble image captured supernova at three different times

Enlarge / On the left, the full Hubble image. On the right, different images of the gravitationally lensed object. (credit: NASA, ESA, STScI, Wenlei Chen, Patrick Kelly)

Over the last few decades, we've gotten much better at observing supernovae as they're happening. Orbiting telescopes can now pick up the high-energy photons emitted and figure out their source, allowing other telescopes to make rapid observations. And some automated survey telescopes have imaged the same parts of the sky night after night, allowing image analysis software to recognize new sources of light.

But sometimes, luck still plays a role. So it is with a Hubble image from 2010, where the image happened to also capture a supernova. But, because of gravitational lensing, the single event showed up at three different locations within Hubble's field of view. Thanks to the quirks of how this lensing works, all three of the locations captured different times after the star's explosion, allowing researchers to piece together the time course following the supernova, even though it had been observed over a decade earlier.

I’ll need that in triplicate

The new work is based on a search of the Hubble archives for old images that happen to capture transient events: something that's present in some images of a location but not others. In this case, the researchers were searching specifically for events that had been gravitationally lensed. These occur when a massive foreground object distorts space in a way that creates a lensing effect, bending the path of light originating behind the lens from Earth's perspective.