Unveiling the Cosmos: How Gravitational Lensing Revealed 44 Hidden Stars

Gravitational lensing refers to the bending effect that massive entities positioned in space-time, such as galaxies and galaxy clusters, exert on light rays, explains McCleary, who focuses on creating instruments to quantify gravitational lensing in remote galaxies.

McCleary illustrates this with the metaphor of a large, stretched rubber sheet. When a heavy item is placed on the sheet, it creates a dip or well, altering the surface. If you attempt to roll an object like a marble from one end of the sheet to the opposite side, it can still reach the other side but will be redirected from its usual course.

“That’s precisely what occurs, but with light rays rather than marbles,” McCleary states. “It’s termed gravitational lensing because in this instance, gravity … functions as a lens, altering light, or concentrating light beams, similarly to how glass modifies the trajectory of light from the sun or a bulb, causing it to focus differently on your retina.”

Typically, the further away a galaxy is, the more challenging it becomes to capture it with any degree of fine detail. Astronomers have been studying individual stars within our own Milky Way and in nearby galaxies such as Andromeda and the Magellanic Clouds. However, “anything beyond our small cosmic neighborhood, the galaxies are too distant for us to identify individual stars,” McCleary notes.

Nevertheless, in this instance, the astronomers managed to perceive the light from 44 stars in the remote Dragon Arc galaxy by utilizing the distortion produced by the immense galaxy cluster Abell 370. This cluster effectively acted as a colossal magnifying glass, positioned between Earth and the Dragon Arc.

McCleary mentions that there was also a dual layer of gravitational lensing. By chance, smaller celestial bodies—free-floating stars that had been dislodged by the forces of the galaxy cluster—were moving past the light emanating from these stars. This occurrence of smaller, moving entities causing a subtle gravitational lensing phenomenon is referred to as microlensing.

“When those stars traverse in front of the image of this background Dragon Arc galaxy, they introduce an extra lensing effect that further amplifies the galaxy and enables us to identify individual stars near the edge of this galaxy’s disc,” McCleary explains.

This dual lensing effect has been utilized previously, but astronomers had only succeeded in capturing an image of seven individual, new stars.

The image obtained by these astronomers is thrilling not only because of the method and technology employed for its capture, McCleary asserts. It effectively opens a new “avenue of exploration” for astrophysicists keen on delving deeper into the universe’s past. While this finding was fortuitous, arising from a specific set of circumstances occurring at the right moment and place, it is not a rarity.

“They’ve discovered this, demonstrating that it’s feasible with JWST, so I anticipate many different teams of researchers will scrutinize the existing JWST observations from various years and attempt to identify whether more detections like these are concealed within the current data,” McCleary states. “I also suspect that this number [of new stars] will rapidly expand from 44 in one cluster to potentially hundreds when looking at a larger collection of clusters.”