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  • Writer's pictureayush devak

Astronomers Witness Light Delayed by Almost 7 Years as It's Warped by a Galaxy Cluster..

Way back in 1979, astronomers spotted two nearly identical quasars that seemed close to each other in the sky. These so-called 'Twin Quasars'are separate images of the same object.
Even more intriguing: the light pathsthat created each image traveled through different parts of the cluster. One path took a little longer than the other.
That meant a flicker in one image of the quasar occurred 14 monthslater in the other.
The reason? The cluster's mass distributionformed a lens that distorted the light and drastically affected the two paths.
Fast-forward to 2022. A team of astronomers from the University of Valencia reported on their study of a similar effect with another distant quasar.
They spent 14 years measuring an even longer time delaybetween multiple images of their target quasar: 6.73 years– the longest ever detected for a gravitational lens.
The galaxy cluster SDSS J1004+4112 plays a role in the delay. The combo of galaxies and dark matter in the cluster is really entangling the quasar light as it passes through.
That's causing the light to travel on different trajectories through the gravitational lens. The result is the same strange time-delayed effect.
The Sloan Digital Sky Surveyfirst discovered cluster SDSS J1004+4112. Hubble Space Telescopeimaged it in 2006. It was the first image of a single quasarwith its light split into five imagesby lensing.
"Measuring these time delayshelps to better understand the properties of galaxies and clusters of galaxies, their mass, and its distribution, in addition to providing new data for the estimation of the Hubble constant," saidJosé Antonio Muñoz Lozano, professor of the Department of Astronomy and Astrophysicsand director of the Astronomical Observatory of the University of Valencia.
In addition to the mass distribution, observational dataalso helps understand other characteristics of the lensing cluster, said Raquel Fores Toribio, a postdoctoral student at the University.
"In particular, it has been possible to constrain the distribution of dark matter in the inner regionof the cluster, since the lensing effectis sensitive not only to ordinary matter but also to dark matter," she said.
She added that calculating the time delay also allows other discoveries, including the distribution of stars and other objects in the area of space between galaxies in the cluster.
In addition, it will help astronomers to 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 bright images of the SDSS J1004+4112 gravitational lensing system.
The observations occurred over 14.5 years at the 1.2-metertelescope located at the Fred Lawrence Whipple Observatory (FLWO, USA), in collaboration with scientists at The Ohio State University (USA).


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