ALMA Uncovers Dark Matter Halo in Distant Galaxy HerS-3 via Rare Einstein Cross

Astronomers have made a groundbreaking discovery using the Atacama Large Millimeter/submillimeter Array (ALMA) by observing the distant galaxy HerS-3, situated an astonishing 11.6 billion light-years from Earth. The ALMA observations have revealed a rare phenomenon known as an Einstein Cross, offering unprecedented insights into the universe's hidden structures, particularly the elusive nature of dark matter.

What is an Einstein Cross?

An Einstein Cross occurs when the light from a distant background galaxy is gravitationally lensed by a massive object, such as another galaxy or a group of galaxies, situated between us and the background source. This gravitational pull warps spacetime, bending and magnifying the light, causing the background galaxy to appear as multiple distinct images. Typically, a perfect alignment can result in four images forming a cross-like pattern, with a fifth, brighter central image often present.

HerS-3: A Unique Cosmic Laboratory

The case of HerS-3 is particularly remarkable due to the presence of a bright fifth central image. Scientists were only able to explain this distinct feature by incorporating a massive halo of dark matter surrounding the lensing galaxy group. This discovery is significant because it provides tangible evidence for the distribution of dark matter, a substance that, despite making up a significant portion of the universe, remains largely invisible and undetectable by conventional means.

The ALMA observations, when superimposed on images from the Hubble Space Telescope (HST), clearly show the lensing effect. The yellow contours from ALMA highlight the millimeter continuum emission, while the HST near-infrared image identifies the four galaxies (G1 to G4) that constitute the lensing galaxy group. The yellow star in the image pinpoints the location of the inferred dark matter halo associated with this group.

Implications for Understanding the Universe

This discovery is not just about observing a beautiful cosmic arrangement; it has profound implications for our understanding of the universe's structure and evolution. Gravitational lensing systems like the Einstein Cross are invaluable tools for astrophysicists, acting as natural cosmic laboratories.

• Dark Matter Mapping: The detailed morphology of the five images of HerS-3, as revealed by ALMA, allows scientists to map the distribution of dark matter with greater precision than ever before. This helps in understanding how dark matter influences the formation and evolution of galaxies.
• Early Universe Studies: The amplification effect of gravitational lensing enables astronomers to study galaxies in the early universe, which would otherwise be too faint to detect. This provides crucial data for understanding the conditions shortly after the Big Bang.
• Measuring Cosmic Expansion: Multiply imaged systems with time-variable sources, such as quasars or supernovae, can be used to measure time delays, which in turn can be used to determine the Hubble constant – a key parameter in understanding the expansion rate of the universe.

This remarkable observation of HerS-3 by ALMA is a testament to the power of modern astronomical instruments and our ever-growing ability to probe the universe's deepest mysteries, shedding light on the invisible forces that shape our cosmos.