(ORDO NEWS) — Back in 1979, astronomers spotted two almost identical quasars in the sky that seemed to be close to each other. These so-called “twin quasars” are actually separate images of the same object.
Even more intriguing, the paths of light that produced each image traveled through different parts of the cluster. One path took a little longer than the other.
This meant that the scintillation in one quasar image occurred 14 months later in the other.
Cause? The mass distribution of the cluster formed a lens that distorted the light and dramatically affected the two paths.
Fast forward to 2022. A group of astronomers from the University of Valencia reported a study of a similar effect with another distant quasar.
They spent 14 years measuring an even greater time delay between multiple images of the target quasar: 6.73 years, the longest ever found for a gravitational lens.
The galaxy cluster SDSS J1004+4112 plays a role in the delay. The combination of galaxies and dark matter in the cluster really confuses the quasar’s light as it passes through it.
This causes the light to follow different paths through the gravitational lens. The result is the same weird delay effect.
“The four quasar images we see actually correspond to one quasar whose light is bent on its way to us by the gravitational field of the galaxy cluster,” said José Antonio Muñoz Lozano, professor in the Department of Astronomy and Astrophysics and director of the Astronomical Observatory of the University of Valencia.
“Because the path that the light rays follow to form each image is different, we observe them at different times; in this case, we have to wait 6.73 years for the signal we observed in the first image to be reproduced in the fourth. one.”
The Sloan Digital Sky Survey has detected SDSS J1004+4112 for the first time. The Hubble Space Telescope took an image of it in 2006. This was the first image of a single quasar whose light was split into five images using a lens.
Gravitational lensing creates an optical effect when light passes through a region of space with a strong gravitational influence.
What do time delays tell astronomers?
The observed time delay gives astronomers some interesting insights into lensing clusters. Galaxy clusters are amazingly massive and are the largest gravitationally bound structures we know of in the universe. Some of them contain thousands of galaxies.
The combined gravity of galaxies, as well as mixed dark matter in a cluster, can entangle light from more distant objects as it passes through or near the cluster. It turns out that the mass of all “substance” 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 about the distribution of matter in the cluster. This includes dark matter. All this helps them understand how this affects the path of light from a distant quasar.
“Measuring these time delays helps to better understand the properties of galaxies and clusters of galaxies, their mass and its distribution, in addition to providing new data for estimating the Hubble constant,” said Lozano.
Understanding mass distribution in Lensing Clusters
In addition to the mass distribution, the observational data also help to understand other characteristics of the lensing cluster, says Raquel Fores Toribio, a graduate student at the university.
“In particular, it became 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,” she said.
She added that the time delay calculation also allows for other discoveries, including the distribution of stars and other objects in the region of space between the galaxies in the cluster.
It will also help astronomers calculate the size of a distant quasar’s accretion disk.
A recently published paper describes the team’s use of new light curves for four bright quasar images. gravitational lensing system SDSS J1004+4112.
The observations were carried out for 14.5 years on the 1.2-meter telescope located at the Fred Lawrence Whipple Observatory (FLWO, USA), in collaboration with scientists from Ohio State University. (USA).
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