Rare 'Carousel Lens' galaxy alignment reveals dark matter secrets

Imagine gazing into the night sky and discovering a cosmic coincidence so rare it’s like finding eight needles perfectly lined up in a haystack. That’s exactly what a team of astronomers has stumbled upon — a unique configuration of galaxies forming what they call the “Carousel Lens.”

This extraordinary find promises to deepen our understanding of the universe, shedding light on some of its most enigmatic components.

“This is an amazingly lucky ‘galactic line-up’ — a chance alignment of multiple galaxies across a line-of-sight spanning most of the observable universe,” says David Schlegel, a co-author of the study.

Finding one such alignment is tough enough, but this discovery is something else entirely. “Finding all of these is like eight needles precisely lined up inside that haystack,” he adds.

The research was conducted by scientists from Berkeley Lab’s Physics Division, utilizing state-of-the-art facilities and data sources. Their collaborative efforts have led to this remarkable discovery, opening new doors in the field of cosmology.

Understanding the Carousel Lens

Why the excitement surrounding the Carousel Lens? This phenomenon features a foreground galaxy cluster that acts as a gravitational lens, revealing seven background galaxies situated billions of light-years away.

Through the gravitationally distorted space-time around the lens, we observe a stunning visual effect that evokes the image of a cosmic carousel gracefully spinning through the expanse of space.

The lensing cluster, situated about 5 billion light-years from Earth, is represented by its four brightest and most massive galaxies, labeled La, Lb, Lc, and Ld.

These galaxies form the foreground of the image. Behind this cluster, seven unique galaxies — numbered 1 through 7 — appear. These galaxies are incredibly distant, ranging from 7.6 to 12 billion light-years away, pushing the limits of our observable universe.

Each of these background galaxies doesn’t just appear once. Due to the gravitational lensing effect, they show up multiple times in the image, labeled with letters like 1a, 1b, and so on.

Their shapes are curved and stretched, creating “fun house mirror” iterations caused by the warped space-time around the massive foreground cluster.

It’s like looking at the same galaxy through different lenses, each distorting it in a unique way.

Einstein Cross in the Carousel Lens

One of the most exciting aspects of this discovery is the identification of an Einstein Cross — the largest known to date.

This phenomenon is showcased in galaxy number 4’s multiple appearances, labeled 4a, 4b, 4c, and 4d.

An Einstein Cross occurs when a single distant galaxy appears four times around a massive foreground object due to gravitational lensing.

It’s a clear sign of the symmetrical distribution of the lens’s mass, which is dominated by invisible dark matter.

How gravitational lensing works

Gravitational lensing happens when light from distant galaxies is bent and magnified as it passes near massive objects like galaxy clusters. This effect was predicted by Albert Einstein’s general theory of relativity.

It’s not just a neat trick of nature; gravitational lensing serves as a powerful tool for astronomers. It allows us to see galaxies that would otherwise be too faint or distant, effectively acting as a natural telescope.

Such precise alignments are extremely rare. Think about it: the chances of multiple galaxies lining up in this way across billions of light-years are astronomically low.

This makes the Carousel Lens not just a visual spectacle but also a unique opportunity for scientific study. It provides an exceptional laboratory for testing theories about the universe’s structure and composition.

How the study was conducted

The research team didn’t just rely on luck; they used a wealth of data from various sources.

They tapped into the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, recent observations from NASA’s Hubble Space Telescope, and computational power from the Perlmutter supercomputer at the National Energy Research Scientific Computing Center.

By combining these resources, they built on earlier studies to identify strong lens candidates, leading to this remarkable find.

“Our team has been searching for strong lenses and modeling the most valuable systems,” explains Xiaosheng Huang, a study co-author and member of Berkeley Lab’s Supernova Cosmology Project, and a professor of physics and astronomy at 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 the galaxies appear through the lens, the multiple images of each of the background galaxies form approximately concentric circular patterns around the foreground lens, as in a carousel.

Significance for dark matter and dark energy

Why is this discovery so important? The Carousel Lens offers a new way to study dark matter and dark energy — two of the most mysterious components of our universe.

Dark matter doesn’t emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects.

By analyzing how the light from these distant galaxies is bent and distorted, scientists can map the distribution of dark matter in the lensing cluster.

Understanding dark energy is even more challenging. It’s the force believed to be driving the accelerated expansion of the universe.

The precise measurements made possible by the Carousel Lens could provide new insights into how dark energy affects the cosmos on large scales.

Looking ahead

It’s worth noting that this study also involved several student researchers. The lead author, William Sheu, was an undergraduate student intern with DESI at the beginning of this study.

Now a Ph.D. student at UCLA and a DESI collaborator, Sheu’s contributions highlight the important role that young scientists play in advancing our understanding of the universe.

“This is an extremely 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 can be leveraged for other scientific applications,” such as investigating the mysteries of dark matter and the accelerating expansion of the universe, driven by dark energy.

So, what does this mean for the future? The Carousel Lens sets the stage for new types of observations and experiments.

It could help refine our models of the universe and perhaps even lead to breakthroughs in physics. The data gathered from this unique alignment will keep astronomers and physicists busy for years to come.

The full study was published in the journal The Astrophysical Journal.

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