Astronomers using NASA’s Hubble Space Telescope have spotted, for the first time, a distant supernova split into four images. The discovery, and subsequent analysis by a research team that includes NYU Physicist Or Graur, will help scientists better understand the amount and distribution of dark matter in this part of the universe.
The four images of the supernova, or exploding star, are caused by the powerful gravity of a foreground elliptical galaxy—primarily composed of older, low-mass stars—that is embedded in a massive cluster of galaxies.
The observation, reported in the latest issue of the journal Science, spotlights an effect called “gravitational lensing”: gravity from both the elliptical galaxy and its galaxy cluster distorts and magnifies the light from the supernova behind it.
“These are new and unique data for the lensing modelers,” explains Graur, an assistant research scientist in NYU’s Department of Physics and a research associate at the American Museum of Natural History. “Once they fold these new data into their models, they will be able to generate predictions of when the supernova might appear next. In a few months or years, when hopefully we see this supernova again, we’ll know which of the modeling teams, if any, were correct.”
Gravitational lensing, first predicted by Albert Einstein, is similar to a glass lens bending light to magnify and distort the image of an object behind it. The multiple images are arranged around the elliptical galaxy in a cross-shaped pattern called an Einstein Cross. The elliptical galaxy and its cluster are 5 billion light-years from Earth. The supernova behind it is 9.3 billion light-years away.
“Scientists are studying galaxy clusters because they can use their lensing effects to map the distribution of dark matter in the cluster,” observes Graur. “These maps will hopefully offer new insights into the nature of dark matter.”
Astronomers have discovered dozens of multiply-imaged galaxies and quasars, but they have never seen a stellar explosion resulting in several images—the cosmological equivalent of discovering a four-leaf, rather than three-leaf, clover.
“It really threw me for a loop when I spotted the four images surrounding the galaxy—it was a complete surprise,” said Patrick Kelly of the University of California, Berkeley, a member of the Grism Lens Amplified Survey from Space (GLASS) collaboration and the Science paper’s lead author.
Graur and his colleagues are part of the Frontier supernova (FrontierSN) team, which is working with the GLASS group to analyze the exploding star and headed by Steve Rodney, an astronomer at Johns Hopkins University.
The Frontier Fields survey is a three-year program that uses Hubble and the gravitational-lensing effects of six massive galaxy clusters to probe not only what is inside the clusters but also what is beyond them. The three-year FrontierSN program studies supernovae that appear in and around the galaxy clusters of the Frontier Fields and GLASS surveys. The GLASS survey is using Hubble’s spectroscopic capabilities to study remote galaxies through the cosmic telescopes of 10 massive galaxy clusters, including the six in the Frontier Fields.