- 3774 - GALAXIES - light delay around galaxies. The combined gravity of the galaxies, plus the intermingled dark matter 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 the cluster is spread out unevenly. That can affect the path of light through the cluster.
--------------------- 3774 - GALAXIES - light delay around galaxies
- Astronomers see multiple images of the same “quasar“. That is because the light took different paths to reach us. They measured a time delay of 6.73 between multiple images of this same quasar. This result, obtained after 14.5 years of observation. This is the longest delay ever detected for a gravitational lens causing light taking different paths to reach us.
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- Galaxy clusters are the largest gravitationally bound structures in the universe and can contain thousands of galaxies. In addition to galaxies and gas, the clusters are mostly made up of “dark matter“, imperceptible by direct detection of light, still unknown.
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- Cosmological models often use “quasars’ , the brightest astronomical objects in the universe, and so-called ‘gravitational lenses’. Gravitational lensing occurs when a massive object is between the observer and a bright celestial body. The massive object warps space-time and modifies the path of light rays passing through it. This is just what a magnifying glass does with light.
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- When observing a distant quasar through a galaxy or cluster of galaxies, if the lensing effect is strong enough, several images of the same celestial body are formed.
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- Astronomers calculated the light curves for the four bright images of the SDSS J1004+4112 gravitational lensing system. The observations were carried out over 14.5 years with the 1.2 meter telescope.
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- The four images of the quasar that we observe actually correspond to a single quasar whose light is curved on its path towards us by the gravitational field of the galaxy cluster”. Since the trajectory followed by the light rays to form each image is different, we observe them at different instants of time; 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.
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- 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 the estimation of the Hubble constant of the universe’s expansion rate.
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- This measurement has made it possible to study the mass distribution of the galaxy cluster. The time delay malws it possible to more accurately reconstruct the mass distribution of the galaxy cluster that acts as a lens bending the light.
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- Gravity really tangled up the light from this distant Quasar. In 1979, astronomers spotted two nearly identical quasars that seemed close to each other in the sky. These “Twin Quasars” are actually separate images of the same object. Even more intriguing: the light paths that created each image traveled through different parts of the cluster.
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- One path took a little longer than the other. That meant a flicker in one image of the quasar occurred 14 months later in the other.
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- In 2022 astronomers reported of a similar effect with another distant quasar. They spent fourteen years measuring an even longer time delay between multiple images of their target quasar. The galaxy cluster SDSS J1004+4112 plays a role in the delay.
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- The galaxies and dark matter in the cluster is really entangling the quasar light as it passes through. That’s causing the light to travel different trajectories through the gravitational lens. The result is the same strange time-delayed effect.
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- The observed time delay provides some interesting clues about lensing clusters. Galaxy clusters are astonishingly massive and the largest gravitationally bound structures we know of in the universe. Some contain thousands of galaxies.
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- Understanding mass distribution in lensing clusters helps us understand 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.
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- 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. It will help astronomers to calculate the size of the distant quasar’s accretion disk.
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- See Review 3773 - CRAB NEBULA - when light can reach us to learn how these time delays are calculated to determine distance.
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December 6, 2022 GALAXIES - light delay around galaxies 3774
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