Astronomers typically cannot resolve individual stars at such extreme distances. They usually only observe the combined light of billions of stars blended together into a single fuzzy glow. However, a team of researchers including Dr. David Lagattuta, an astronomer at Durham University, utilized the immense gravity of the Abell 370 galaxy cluster to magnify the light from the Dragon Arc, a distorted streak of light originating from a background galaxy.
The Mechanics of Gravitational Lensing
Gravitational lensing occurs when the sheer mass of a massive cosmic object warps the fabric of spacetime. Light from a distant galaxy travels in all directions. When a massive galaxy cluster sits between the observer and the target, its gravity bends the light paths. This focuses the light toward the observer, making the distant object appear significantly brighter and larger. “Instead of the lens being a piece of glass, it’s a big galaxy,” Dr. Lagattuta explained.
The concept of gravitational lensing has been theorized since the days of Albert Einstein in the early 1900s. However, it took until 1979 for astronomers to actually find gravitational lenses. A few years later, they spotted an “odd blue arc” in Abell 370, which became known as the Dragon Arc. It was the first lens arc ever discovered.
To find the 44 individual stars, the research team employed a specialized subset of this technique called microlensing. While the massive, invisible halo of dark matter in Abell 370 acts as a “macrolens,” individual stars within the cluster function as additional “microlenses.” This compounded magnification effect multiplied the resolving power, allowing the James Webb Space Telescope to isolate individual stars within the Dragon Arc. The sheer number of stars discovered far exceeded expectations. “It was a real wow moment,” Dr. Lagattuta said.
Abell 370 and the Dragon Arc
Abell 370 sits roughly 5 billion light-years from Earth. The Dragon Arc, the target of this study, lies a few billion light-years beyond the cluster, at a distance of 8.5 billion light-years. Because galaxy clusters are so massive, they make the best natural lenses. Abell 370 is one of the most prominent lenses known to astronomers.
The scale of this observation is difficult to overstate. Looking at an individual star 8.5 billion light-years away means we are seeing light that left that star long before our own solar system formed. This provides a literal look back in time, offering a snapshot of the universe during a critical phase of its development.
Why the James Webb Space Telescope Succeeds
The Hubble Space Telescope is a fantastic instrument, but the James Webb Space Telescope possesses distinct advantages for this type of deep-space observation. The primary benefit is resolution. Where older instruments might show a fuzzy blob that could be a star, a star cluster, or a patch of gas, JWST resolves a distinct point of light. “With JWST that uncertainty goes away. You see a dot, which means it must be some kind of star,” noted Dr. Lagattuta.
Furthermore, JWST observes in longer, redder wavelengths of light. Stars are frequently surrounded by cosmic dust created during their formation. This dust scatters visible light, rendering optical telescopes ineffective. JWST pierces through these dusty regions, revealing the stars hidden within. This capability has been a “real gamechanger” for deep field astronomy.
Probing Cosmic Noon and Stellar Evolution
The newly discovered stars exist during a critical era known as Cosmic Noon. This period represents the midpoint of the Universe’s timeline, an epoch characterized by rampant star formation. During Cosmic Noon, galaxies similar to our Milky Way were producing about 1,000 new stars per year. Today, the Milky Way produces roughly one new star annually.
Studying stars from this era provides a crucial anchor point for understanding stellar evolution. The earliest stars formed right after the Big Bang from pristine hydrogen and lived and died in unique ways. Their supernova explosions injected the universe with heavier elements, altering how subsequent stars formed. Observing stars from Cosmic Noon bridges the gap between these early hydrogen-burning stars and the metal-enriched stars we see today.
Unlocking the Secrets of Dark Matter
Beyond stellar evolution, these microlensing observations offer a unique window into the nature of dark matter. Dark matter is the mysterious, invisible substance that holds galaxies together. By mapping where the microlensing events occur, astronomers can infer the position and density of the dark matter acting as the macrolens.
Researchers can take competing dark matter theories—such as whether it consists of a certain type of particle or a type of wave—and calculate what its distribution should look like. By comparing these theoretical models to the actual microlensing events observed in the data, scientists can refine or eliminate dark matter models. This work is ongoing and represents one of the most promising avenues for finally understanding the universe’s most elusive substance.
What Happens Next
Moving forward, astronomers will continue monitoring the Dragon Arc and other heavily lensed galaxies to capture transient microlensing events. As the James Webb Space Telescope accumulates more data over its lifetime, scientists hope to refine dark matter models and uncover even older stars, pushing closer to the universe’s dawn.
The success of this technique proves that combining advanced infrared optics with natural cosmic magnifying glasses will fundamentally reshape our understanding of the cosmos. Future surveys will likely target other massive galaxy clusters, turning the entire sky into a hunting ground for individual stars that were previously lost in the glare of their host galaxies.
— Priya Nair, science desk, AXO News