The sky is full of magnifying glasses that act as natural telescope lenses, allowing distant objects, normally too faint for even the most powerful telescopes, to be studied. An astronomer from the University of California, Berkeley, along with data from the Hubble Space Telescope (HST) and the Keck Observatory, has found a cluster of galaxies that are gravitationally bending and magnifying light, creating four separate images of a far-away supernova.
According to the press release from UC Berkeley, the "Einstein cross" allows the study of distant supernova and the distribution of dark matter in the bending galaxy, which is part of a known galaxy cluster called MACS J1149.6+2223.
"Basically, we get to see the supernova four times and measure the time delays between its arrival in the different images, hopefully learning something about the supernova and the kind of star it exploded from, as well as about the gravitational lenses," said UC Berkeley postdoctoral scholar Patrick Kelly, according to the press release. "That will be neat."
Kelly, a member of the Grism Lens-Amplified Survey from Space (GLASS) team led by Tommaso Treu at UCLA, discovered the supernova while looking through infrared images taken Nov. 10, 2014, by the HST.
"It's a wonderful discovery," Alex Filippenko, a UC Berkeley professor of astronomy and a member of Kelly's team, said according to the press release. "We've been searching for a strongly lensed supernova for 50 years, and now we've found one. Besides being really cool, it should provide a lot of astrophysically important information."
A bonus of the peculiar nature of the gravitational lensing is that astronomers can check back for a replay within the next five years. Since light can take many paths around and through a gravitational lens, the light arrives at Earth at different times. A computer model shows that researchers missed the exploding star in action 50 years ago and again 10 years ago, but the images should repeat in a few years.
"The longer the path length, or the stronger the gravitational field through which the light moves, the greater the time delay," Filippenko.said, according to the press release.
Kelly, Filippenko and their colleagues have named the distant supernova SN Refsdal in honor of Sjur Refsdal, the late Norwegian astrophysicist and pioneer of gravitational lensing studies. According to the press release, it is located about 9.3 billion light-years away (redshift = 1.5), near the edge of the observable universe, while the lensing galaxy is about 5 billion light-years (redshift = 0.5) from Earth.
"These gravitational lenses are like a natural magnifying glass. It's like having a much bigger telescope," Kelly said, according to the press release. "We can get magnifications of up to 100 times by looking through these galaxy clusters."
"We have seen many distant quasars appear as Einstein crosses, but this is the first time a supernova has been observed in this way," Filippenko said, according to the press release. "This short-lived object was discovered only because Pat Kelly very carefully examined the HST data and noticed a peculiar pattern. Luck comes to those who are prepared to receive it."
The results will be published in a special edition of Science magazine commemorating the centenary of Albert Einstein's general theory of relativity.
UC Berkeley co-authors of the paper, in addition to Kelly and Filippenko, are postdoctoral scholars Melissa Graham and Bradley Tucker. Other contributing authors are Steven A. Rodney, Tommaso Treu, Ryan J. Foley, Gabriel Brammer, Kasper B. Schmidt, Adi Zitrin, Alessandro Sonnenfeld, Louis-Gregory Strolger, Or Graur, Saurabh W. Jha, Adam G. Riess, Marusa Bradac, Benjamin J. Weiner, Daniel Scolnic, Matthew A. Malkan, Anja von der Linden, Michele Trenti, Jens Hjorth, Raphael Gavazzi, Adriano Fontana, Julian C. Merten, Curtis McCully, Tucker Jones, Marc Postman, Alan Dressler, Brandon Patel and S. Bradley Cenko.
The UC Berkeley work was supported by the Christopher R. Redlich Fund, the TABASGO Foundation and the National Science Foundation (grant AST-1211916).
