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EI2GYB > ASTRO 08.10.25 12:46l 41 Lines 5242 Bytes #59 (0) @ WW
BID : 46335_EI2GYB
Subj: Gravitational lenses imaged by Webb during its first run
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Gravitational lenses imaged by Webb during its first run
Periodically, the European Space Agency (ESA) releases images that provide breathtaking views of the cosmos, courtesy of its premier missions. This includes a relative newcomer to party with the ESA/Webb Picture of the Month, which showcases the high-resolution and ultra-sensitive capabilities of the James Webb Space Telescope (JWST). This month's feature: eight stunning images of gravitationally-lensed galaxies observed by Webb during its Cycle 1 General Observation (GO) surveys. The study of these lensed galaxies is providing insight into the early universe and how galaxies have evolved with time.
Gravitational lenses were first predicted by Einstein's Theory of General Relativity (GR), which states that gravity is the result of massive objects altering the curvature of spacetime around them. When galaxies and galaxy clusters align with more distant objects, the lensing effect can cause light from these sources to become warped and amplified, allowing astronomers to study objects that would otherwise be very difficult to observe. Depending on the alignment, the light from distant objects can form different shapes, such as an arc, a circle (an "Einstein ring"), or multiple images of the same source (an "Einstein Cross").
The eight lensed galaxies featured in this image were observed as part of the COSMOS-Web program, a 255 hour wide-field Cycle treasury program combining data from Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). Otherwise known as the JWST Cosmic Origins Survey, this program aimed to study galaxies that existed during the "Epoch of Reionization" (ca. 200 million-1 billion years after the Big Bang), when the first stars and galaxies reionized the neutral hydrogen that permeated the universe, causing it to become "transparent" (visible to instruments today).
Based on these observations, researchers carried out the COSMOS-Web Lens Survey (COWLS) to search for gravitational lenses. This consisted of inspecting more than 42,000 galaxies by eye, from which 400 were selected as promising lensing candidates. The eight galaxies featured in the Picture of the Month were considered especially impressive because they cover a vast range of cosmic history between the lensing and lensed galaxies. While the foreground galaxies are dated to 2.7 to 8.9 billion years after the Big Bang, the background galaxies existed when the universe was much younger.
In particular, the background galaxy in the top row, left of center (the "COSMOS-Web ring") existed when the universe was less than 1 billion years old, placing it in the Era of Reionization-a period that is impossible to observe with optical telescopes. For this reason, astronomers and cosmologists refer to this period as the "Cosmic Dark Ages," which was inaccessible until the deployment of the JWST.
Another candidate, just to the right of the COSMOS-Web ring, is also an example of an Einstein ring, but appears smaller and less discernible. This lensing system (COSJ100018+022138) was previously confirmed by the venerable Hubble Space Telescope, but revealed in greater detail by Webb. While the elliptical lensing galaxy in the foreground appears as it did roughly 4 billion years after the Big Bang, the blue-lensed galaxy existed when the universe was less than 2 billion years old.
Other galaxies appear as arcs and have an orange hue, whereas some appear reddish and compact (see image above). These latter objects could be examples of the "Little Red Dots" (LRDs) that Webb revealed, which have puzzled astronomers ever since. These images not only demonstrate Webb's capabilities as an observatory but also provide a glimpse into its primary purpose: to trace the evolution of galaxies and the cosmos from the very beginning to the modern era.
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