About 9.3 billion years ago, a supernova exploded in our universe. Since then, its light has been traveling the billions of light years it takes to get to our little planet we call home. But in between this supernova and Earth, there happens to be a massive galaxy, within a cluster of galaxies, which has had an interesting effect on the path of the light coming from this exploded star.
Astronomers using the Hubble Space Telescope have captured a picture of a distant galaxy so massive that its gravitational field is bending the light from an even more distant supernova.
The image, released Thursday, shows how the flash from the supernova’s blast has been warped into four points of light surrounding an elliptical galaxy in a cluster called MACS J1149.2+2223, which is 5 billion light-years away in the constellation Leo.
“It was predicted 50 years ago that a supernova could be gravitationally lensed like this, but it’s taken a long time for someone to find an example,” lead study author Patrick Kelly, an astronomer at the University of California, Berkeley said “It’s fun to have been able to find the first one.”
Australian National University astronomer Brad Tucker, a co-author of the paper, said the NASA telescope captured the exploding supernova by chance during a survey looking for something else. However he said the keen eye of Dr Kelly had spotted something special, particularly given the one-off explosion was seen multiple times.
“Because there are a lot of things in the universe affecting light, like dark matter, dark energy and gravity, the images will not only appear in different places but at different times,” Dr Tucker said.
The first gravitational lens was discovered in 1979 and since then, astronomers have discovered the universe is filled with them. While it was predicted that a supernova could be gravitationally lensed, Tucker and his colleagues provided the first example of it.
“It’s a relic of a simpler time, when the universe was still slowing down and dark energy was not doing crazy stuff,” Tucker said. “We can use that to work out how dark matter and dark energy have messed up the universe.”
Dark matter is an invisible substance that cannot be seen but binds galaxies together. It makes up most of the matter in the universe but its nature is unknown.
Even more mysterious, dark energy produces an “anti-gravity” force that is causing galaxies to fly apart at an accelerating rate.
Because the lensing effect also magnifies the supernova, it offers scientists a window into the distant past by uncovering light that has spent billions of years crossing the universe.
With these image copies of the supernova, Kelly says they can also learn more about the mass distribution within the galaxy, as well as measure the expansion of the universe. By comparing the times it takes for future images of the supernova to appear, scientists can calculate just how massive and dense that galaxy is, as well as how fast our universe is moving outward.
The scientists detailed their findings in the March 6 issue of the journal Science.
Bottom line: A gravitational lens is a large galaxy or group of galaxies that bends or “lenses” light from a distant source as it travels towards an observer. The effect was predicted by Einstein’s general theory of relativity and the first such lens was discovered in 1979. Sometimes, the distant light source, lensing galaxy and the observer line up precisely, and we can see an “Einstein ring” – a perfect loop of light from the source encircling the lensing mass. But if there is any misalignment along the way, we observe partial arcs or spots. Depending on the relative positions of the bodies, four such spots can be seen, forming an Einstein cross. The lensing effect serves as a “natural telescope” for astronomers, who can determine the mass of the lensing galaxy and its dark-matter content based on the amount of distortion observed.