Astronomers have made a groundbreaking discovery involving two galaxies aligned in such a way that their combined gravitational effects create what is known as a compound lens. This phenomenon has been explored in detail by an international team of researchers who have documented their findings and shared their work on the arXiv preprint server.
For many years, scientists have observed galaxies bending light, a phenomenon predicted by Albert Einstein’s theory of general relativity. This effect, known as gravitational lensing, occurs when a massive object, like a galaxy or a cluster of galaxies, distorts the space around it. As light from objects behind these masses passes through this distorted space, it bends, often producing magnified, stretched, or multiple images of the background object. In previous studies, astronomers have observed how individual galaxies, particularly elliptical ones, can act as gravitational lenses that brighten and distort the light from sources behind them.
In their latest research, the team has identified something that has not been observed before: two galaxies aligned in such a way that their gravitational fields combine to form a compound lens. In optics, a compound lens is a system made of two or more lenses designed to work together to correct optical distortions, such as chromatic aberration. In space, however, this effect is created naturally by the gravitational pull of the two galaxies working in tandem. For this to happen, these galaxies must align almost perfectly with one another and with a light source behind them, such as a quasar. This rare alignment results in a more complex lensing effect that can produce intricate light patterns, which are difficult to interpret without detailed analysis.
The system under investigation, known as J1721+8842, was initially believed to consist of a single elliptical galaxy acting as a gravitational lens for a quasar located behind it. The quasar’s light, bending around the foreground galaxy, was thought to be responsible for creating four distinct images—a common feature in gravitational lensing known as an “Einstein cross.” However, after collecting and analyzing data over a two-year period, the researchers noticed peculiar variations in the quasar’s light patterns that could not be fully explained by a single lens.
Upon closer examination, the team found additional, smaller bits of light that appeared to be duplicates of the main four lights seen earlier. This observation was puzzling because these smaller lights seemed to mirror the primary set. Further analysis revealed that all six observed light sources originated from the same quasar, indicating a more complex lensing structure at play.
To gain a clearer picture, the researchers integrated data from the James Webb Space Telescope (JWST), which provided much higher resolution images. This data revealed a reddish ring intertwined with the previously observed lights. Initially, this ring was assumed to be an Einstein ring, a circular image of a background source formed when light from that source is bent by a single gravitational lens. However, the enhanced clarity provided by the JWST images led to a surprising conclusion: the reddish ring was actually due to the presence of a second lensing galaxy. This discovery confirmed the presence of a natural compound lens system.
To validate their observations, the team developed a computer model to simulate the effects of gravitational lensing with two aligned galaxies. The model confirmed that the complex light patterns observed were indeed the result of the combined gravitational influence of both galaxies acting as a compound lens. This rare alignment not only magnified the light from the distant quasar but also created multiple images, some of which were duplicated and distorted in ways that would not be possible with a single lens.
This discovery has significant implications for astrophysics, particularly in refining measurements of the Hubble constant, which is a critical value used to determine the rate of expansion of the universe. For years, there has been a persistent discrepancy between measurements of the Hubble constant obtained through observations of the cosmic microwave background and those based on observations of galaxies and supernovae. A compound lens system like the one discovered could provide a new way to study gravitational lensing in more detail, potentially leading to more accurate calculations of the Hubble constant. If the measurement techniques can be refined using insights from this new compound lens system, it may help resolve the ongoing debate regarding the universe’s rate of expansion.
This finding not only expands our understanding of gravitational lensing but also opens up new avenues for exploring the cosmos. By identifying and studying more systems like J1721+8842, astronomers may be able to develop new methods for probing the structure of the universe, improving our understanding of fundamental cosmic parameters.