Dark matter and Einstein rings solve ancient galaxy mystery

A team of researchers led by Hai-Bo Yu has shed new light on the enigmatic nature of dark matter through the lens of an ancient galaxy.

The study focuses on JWST-ER1g, a massive ancient galaxy discovered by the James Webb Space Telescope (JWST) last September, which formed when the universe was just a quarter of its current age.

Surprisingly, JWST-ER1g is associated with an Einstein ring, a phenomenon predicted by Einstein’s theory of general relativity. The galaxy acts as a lens, bending light from a distant source, which then appears as a ring.

This phenomenon, known as strong gravitational lensing, allows researchers to calculate the total mass enclosed within the ring, which consists of both stellar and dark matter components.

Unveiling the dark matter halo

“If we subtract the stellar mass from the total mass, we get the dark matter mass within the ring,” explained Professor Yu, a professor of physics and astronomy at the University of California, Riverside.

“But the value for the dark matter mass seems higher than expected. This is puzzling. In our paper, we offer an explanation,” Yu concluded.

The team proposes that the high density of dark matter in JWST-ER1g may be due to the compression of the dark matter halo surrounding the galaxy.

As ordinary matter, such as pristine gas and stars, collapses and condenses into the dark matter halo, it may compress the halo, leading to a higher density of dark matter.

Demao Kong, a second-year graduate student at UCR who led the analysis, stated, “Our numerical studies show that this mechanism can explain the high dark matter density of JWST-ER1g — more dark matter mass in the same volume, resulting in higher density.”

Understanding Einstein rings

Einstein rings are a stunning cosmic phenomenon that occurs when a massive object, such as a galaxy or a black hole, acts as a gravitational lens.

The immense gravitational field of the object bends and magnifies the light from a more distant source, such as another galaxy or a quasar, located directly behind it. The result is a near-perfect ring of light that appears around the lensing object.

Science behind Einstein rings

Albert Einstein’s theory of general relativity predicts the existence of gravitational lensing. According to this theory, massive objects warp the fabric of spacetime, causing light to follow curved paths instead of straight lines.

When a distant light source, a massive lensing object, and an observer align perfectly, an Einstein ring forms.

The size and shape of an Einstein ring depend on various factors, such as the mass of the lensing object, the distance between the lensing object and the light source, and the alignment of the observer.

The more massive the lensing object and the more precise the alignment, the more prominent the Einstein ring appears.

Studying the universe through Einstein rings

Astronomers use Einstein rings as powerful tools to study the universe. By analyzing the light from these rings, researchers can determine the mass and distribution of both visible and dark matter within the lensing object.

This information helps scientists better understand the structure and evolution of galaxies and galaxy clusters.

Moreover, Einstein rings act as cosmic magnifying glasses, allowing astronomers to observe distant galaxies and quasars that would otherwise be too faint to detect.

By studying these amplified images, researchers can learn about the early universe and the formation of galaxies billions of years ago.

Notable examples of Einstein rings

One of the most famous Einstein rings is the Cosmic Horseshoe, discovered in 2007. This ring, created by a massive galaxy cluster, magnifies the light from a distant galaxy by a factor of 300, providing an unprecedented view of the early universe.

Another remarkable example is the Einstein ring SDSS J1038+4849, which consists of two concentric rings. This rare configuration arises when two distant galaxies align perfectly with a massive galaxy cluster in the foreground, creating a double Einstein ring.

As astronomers continue to explore the cosmos with increasingly powerful telescopes, such as the James Webb Space Telescope, they are likely to discover more Einstein rings, further expanding our understanding of the universe and its hidden wonders.

Unique opportunity for dark matter research

JWST-ER1g, formed 3.4 billion years after the Big Bang, provides a unique opportunity to study dark matter, which makes up 85% of the universe’s matter but has never been detected in laboratories.

Daneng Yang, a postdoctoral researcher at UCR and co-author on the paper, emphasized the significance of this strong lensing object.

“This strong lensing object is unique because it has a perfect Einstein ring, from which we can obtain valuable information about the total mass within the ring, a critical step for testing dark matter properties,” Yang explained.

Continuing the quest to understand dark matter

In summary, the discovery of JWST-ER1g and its associated Einstein ring by the James Webb Space Telescope has opened up new avenues for studying dark matter, a mysterious component that makes up 85% of the universe’s matter.

Through the analysis of this unique strong lensing object, the team of researchers led by Professor Hai-Bo Yu has proposed a compelling explanation for the unexpectedly high density of dark matter within the galaxy.

As the James Webb Space Telescope continues to probe the depths of the universe, revealing ancient galaxies and cosmic phenomena, we can expect more groundbreaking discoveries that will further unravel the enigmatic nature of dark matter and enhance our understanding of the cosmos.

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

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