Gravitational Lensing Lets Astronomers See Reruns of aSupernova Exploding

A rare phenomenon allowed astronomers to witness a perhaps once-in-a-lifetime event: reruns of a supernova exploding.

Using the Hubble Space Telescope, a team of astronomers captured the unique yet all-so-rare moment when a supernova blew itself to smithereens. Yet while some are only lucky enough to see such an event once, “gravitational lensing” allowed astronomers to watch the same supernova explode over and over again.

Gravitational lensing occurs when massive galaxies or clusters of galaxies are so large that they are able to bend the light rays passing through. When looking towards that particular spot, and the Earth is properly aligned with the objects in question, small celestial bodies can sometimes become magnified by the massive lens-like galaxy located in front of it. And while such a phenomenon in itself is exquisitely special, the universe added a bit more spice to the concoction.

As the astronomers who captured this unique event reported in Thursday’s issue of science, the exceptional lensing properties of the galaxy located between the exploding supernova and the Hubble Space Telescope allowed that the same star appear four times around the galaxy. Such an event is dubbed an Einstein Cross (as the famous physicist predicted such a phenomenon approximately a century ago).

This multiply-lensed supernova will continue to get brighter over the next decade, astronomers explain, as the cosmos will continue replaying the supernova’s explosion in different spots of the galaxy.

“Basically, we get to see the supernova four times and measure the time delays between its arrival in the different images.”

Patrick Kelly, study author and University of California astronomer said.

Astronomers explain that this supernova (located more than 9 billion light years away) would have been much to faint to have been picked up on Earth even if it would have had one galaxy acting as a lens. But in this particular case, the star’s explosions were captured by a cluster of galaxies which are believed to have produced three of the images captured. A final galaxy, astronomers added, caught the event again, bending the light yet again and producing the fourth image.

The supernova was magnified over 20 times.

While astronomers have seen gravitational lensing and supernovae before, there is one thing they hadn’t yet surprised.

“We’ve even seen lensed supernovae before. But this multiple image is what we have all been hoping to see.”

Harvard-Smithsonian Center for Astrophysics supernova expert, Robert Kirshner said.

There is yet another curious fact about this particular supernova. Despite the fact that normally, a supernova experiences a peak in brightness and then dwindles, scientists have been observing that its brightness continues to increase. Moreover, this supernova’s light spectrum isn’t like anything that astronomers had studied on any of the other known supernovae types. Which begs the question: could this gravitationally-lensed supernova harbor even more secrets? Or could it just be that at the time when this supernova was forming, nine billion years ago, stars followed other rules than astronomers have identified.

Perhaps the composition of the younger universe, where fewer metals were to be found, allowed such stars to become bigger but also die faster.

“One of the big open areas of research is determining exactly what changes with cosmic time or distance.”

study co-author, Ryan Foley mentioned, underlining the importance of continued observation of the brightening explosions.