Astronomers using the James Webb Space Telescope have peered through cosmic dust and magnified space-time using massive galaxy clusters like Abell 370 and Pandora’s Cluster. By combining macrolensing with stellar microlensing, researchers uncovered dozens of previously unseen distant stars, a dark matter map of 800,000 galaxies, and thousands of early cosmic sources.
When astronomers look deep into the universe, nature occasionally provides an instrument far more powerful than any human-built mirror. The sheer mass of enormous cosmic objects warps spacetime and can magnify light from distant sources, enabling researchers to see objects that would otherwise remain invisible. This natural magnifying glass effect, known as gravitational lensing, is rooted in Einstein’s early 20th-century theories, but instruments like NASA’s James Webb Space Telescope are pushing the technique into entirely new territory.
Unlocking the Dragon Arc in Abell 370
The galaxy cluster Abell 370, located about 5 billion light-years away, serves as one of the universe’s most powerful cosmic lenses. Within this cluster sits the Dragon Arc, the first lens arc ever discovered, formed by light from a galaxy situated roughly 8.5 billion light-years away. While researchers understood the macrolensing effects of massive galaxy clusters for decades, combining that large-scale magnification with a secondary technique called microlensing changed what telescopes could resolve.
By utilizing JWST, astronomers discovered 44 individual stars within the Dragon Arc—far more than anyone expected to find. Furthermore, JWST’s ability to observe longer, redder infrared wavelengths allows it to pierce through the cosmic dust clouds that typically scatter optical light and obscure newborn stars.
Mapping Invisible Dark Matter Across Sextans
Gravitational lensing does not merely bring distant stars into view; it also exposes the invisible scaffolding of the universe. In a sprawling region of the sky located in the constellation Sextans, researchers utilized Webb data to map dark matter across an area roughly two and a half times the size of the full Moon. Because dark matter emits, reflects, and absorbs no light, scientists map its distribution by measuring its gravitational influence on regular matter.
While ground-based observatories and NASA’s Hubble Space Telescope previously mapped this region as part of the Cosmic Evolution Survey, the NASA data reveals about 10 times more galaxies than ground-based maps and twice as many as Hubble’s view. The updated map captures new clumps of dark matter at a higher resolution. To refine distance measurements for these galaxies, the research team relied on Webb’s Mid-Infrared Instrument, managed through launch by the Jet Propulsion Laboratory.
Discovering 50,000 Sources in Pandora’s Cluster
The ambition of Webb’s deep-field imaging is perhaps best illustrated in Pandora’s Cluster, also designated as Abell 2744. In this region, multiple massive galaxy clusters merge to form a megacluster whose combined gravitational pull warps spacetime on a massive scale. By combining Webb’s infrared instruments with this natural lens, astronomers compiled an image representing 50,000 sources of near-infrared light.
Many of these distant, lensed galaxies appear red and distorted into elongated arcs. Among the unconfirmed red sources is an extremely compact dot that researchers suspect could be an early supermassive black hole. Rachel Bezanson of the University of Pittsburgh is associated with the image.
Next Steps for Deep-Field Cosmic Surveys
Scientists will use Webb’s Near-Infrared Spectrograph instrument to capture distance measurements and compositional details for selected red sources. These spectroscopic analyses will determine the true nature of compact objects like potential early black holes, providing crucial data on how galaxies evolved from the early universe.
