In a rare and extraordinary discovery, researchers have identified a novel configuration of galaxies that form essentially the most exquisitely aligned gravitational lens found to this point. The Carousel Lens is a large cluster-scale gravitational lens system that may enable researchers to delve deeper into the mysteries of the cosmos, including dark matter and dark energy.
“That is an amazingly lucky ‘galactic line-up’ — a likelihood alignment of multiple galaxies across a line-of-sight spanning many of the observable universe,” said David Schlegel, a co-author of the study and a senior scientist in Berkeley Lab’s Physics Division. “Finding one such alignment is a needle within the haystack. Finding all of those is like eight needles precisely lined up inside that haystack.”
The Carousel Lens is an alignment consisting of 1 foreground galaxy cluster (the ‘lens’) and 7 background galaxies spanning immense cosmic distances and seen through the gravitationally distorted space-time across the lens. Within the dramatic image below:
- The lensing cluster, positioned 5 billion light years away from Earth, is shown by its 4 brightest and most massive galaxies (indicated by La, Lb, Lc, and Ld), and these constitute the foreground of the image.
- Seven unique galaxies (numbered 1 through 7), appear through the lens. These are positioned far beyond, at distances from 7.6 to 12 billion light years away from Earth, approaching the limit of the observable universe.
- Each galaxy’s repeated appearances (indicated by each number’s letter index, e.g., a through d) show differences in shape which are curved and stretched into multiple “fun house mirror” iterations attributable to the warped space-time across the lens.
- Of particular interest is the invention of an Einstein Cross — the biggest known to this point — shown in galaxy number 4’s multiple appearances (indicated by 4a, 4b, 4c, and 4d). This rare configuration of multiple images across the center of the lens is a sign of the symmetrical distribution of the lens’ mass (dominated by invisible dark matter) and plays a key role within the lens-modeling process.
Light traveling from far-distant space will be magnified and curved because it passes through the gravitationally distorted space-time of nearer galaxies or clusters of galaxies. In rare instances, a configuration of objects aligns nearly perfectly to form a robust gravitational lens. Using an abundance of latest data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, recent observations from NASA’s Hubble Space Telescope, and the Perlmutter supercomputer on the National Energy Research Scientific Computing Center (NERSC), the research team built on their earlier studies (in May 2020 and Feb 2021) to discover likely strong lens candidates, laying the groundwork for the present discovery.
“Our team has been looking for strong lenses and modeling the most useful systems,” explains Xiaosheng Huang, a study co-author and member of Berkeley Lab’s Supernova Cosmology Project, and a professor of physics and astronomy on the University of San Francisco. “The Carousel Lens is an incredible alignment of seven galaxies in five groupings that line up nearly perfectly behind the foreground cluster lens. As they seem through the lens, the multiple images of every of the background galaxies form roughly concentric circular patterns across the foreground lens, as in a carousel. It’s an unprecedented discovery, and the computational model generated shows a highly promising prospect for measuring the properties of the cosmos, including those of dark matter and dark energy.”
The study also involved several Berkeley Lab student researchers, including the lead writer, William Sheu, an undergraduate student intern with DESI at the start of this study, now a PhD student at UCLA and a DESI collaborator.
The Carousel Lens will enable researchers to review dark energy and dark matter in entirely recent ways based on the strength of the observational data and its computational model.
“That is an especially unusual alignment, which by itself will provide a testbed for cosmological studies,” observes Nathalie Palanque-Delabrouille, director of Berkeley Lab’s Physics Division. “It also shows how the imaging done for DESI will be leveraged for other scientific applications,” similar to investigating the mysteries of dark matter and the accelerating expansion of the universe, which is driven by dark energy.
