In 1979, astronomers spotted two nearly identical quasars that appeared close to each other in the sky. These so-called “twin quasars” are actually separate images of the same object.
Even more intriguing: the light paths that created each image ran through different parts of the cluster. One path took a little longer than the other.
This meant that a flicker in one image of the quasar occurred 14 months later in the other.
The reason? The mass distribution of the cluster formed a lens that distorted the light and significantly affected both paths.
Fast forward to 2022. A team of astronomers from the University of Valencia have reported on their study of a similar effect with another distant quasar.
They spent 14 years measuring an even longer delay between multiple images of their target quasar: 6.73 years – the longest ever detected for a gravitational lens.
Galaxy cluster SDSS J1004+4112 plays a role in the delay. The combination of galaxies and dark matter in the cluster really entangles the light from the quasar as it passes through it.
This causes the light to travel different paths through the gravitational lens. The result is the same strange delayed effect.
“The four images of the quasar we observe actually correspond to a single quasar whose light is bent on its way towards us by the gravitational field of the galaxy cluster,” said José Antonio Muñoz Lozano, a professor in the Department of astronomy and astrophysics and director of the Astronomical Observatory of the University of Valencia.
“The trajectory followed by the light rays to form each image being different, we observe them at different times; in this case, it takes 6.73 years for the signal we observed in the first image to reproduce in the fourth. a.”
The Sloan Digital Sky Survey first discovered the SDSS J1004+4112 cluster. The Hubble Space Telescope photographed it in 2006. It was the first image of a single quasar with its light split into five images per lens.
A quick graphical guide to the lens of a quasar
Gravitational lensing creates an optical effect when light passes through a region of space with a strong gravitational influence.
What do the delays tell astronomers?
The observed delay holds out some interesting clues about lens clusters before astronomers. Galaxy clusters are surprisingly massive and are the largest gravitational structures we know of in the universe. Some contain thousands of galaxies.
The combined gravity of the galaxies and the dark matter mixed in the cluster can entangle light from more distant objects as it passes through or near the cluster. It turns out that the mass of all “things” in the cluster is unevenly distributed. This can affect the path of light through the cluster.
So astronomers need all the data they can get on the distribution of matter in a cluster. This includes dark matter. All of this helps them understand how it affects the path of light from a distant quasar.
“Measuring these delays helps to better understand the properties of galaxies and galaxy clusters, their mass and its distribution, in addition to providing new data for the estimation of the Hubble constant,” Lozano said.
Understanding Mass Distribution in Lens Clusters
In addition to mass distribution, observational data also help understand other features of the lens cluster, said Raquel Fores Toribio, a postdoctoral student at the university.
“In particular, it was possible to limit the distribution of dark matter in the inner region of the cluster, since the lensing effect is sensitive not only to ordinary matter but also to dark matter,” he said. she stated.
She added that calculating the time lag also allows for other discoveries, including the distribution of stars and other objects in the area of space between the galaxies in the cluster.
Additionally, it will help astronomers calculate the size of the distant quasar’s accretion disk.
A recently published paper describes the team’s use of new light curves for the four light images of the SDSS J1004+4112 gravitational lens system.
The observations took place over 14.5 years at the 1.2-meter telescope located at the Fred Lawrence Whipple Observatory (FLWO, USA), in collaboration with scientists from Ohio State University (USA).
This article was originally published by Universe Today. Read the original article.
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