A new Hubble Space Telescope image peers into the lair of a cosmic leviathan, a monstrous cluster of galaxies located nine billion light-years away in the constellation Draco.
Like a sea monster in ancient myth submerged and waiting to snatch hapless sailors to their doom, this celestial beast can be seen from the ripples that surround it. However, this leviathan is so titanic that the waves do not travel across the surface of an ocean or lake, but are distortions in the structure of space time itself.
This particular galaxy cluster, known as eMACS J1823.1+7822, is one of five selected for observation by Hubble astronomers to determine the strength of this “warp” effect, which was first predicted by Albert Einstein’s theory of general relativity.
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Sometimes called Einstein’s geometric theory of gravity, the 1915 theory predicts that just as bowling balls placed on a springboard create a depression, objects with mass cause the very fabric of space to deform. time. This curvature gives rise to the force of gravity. And the greater the mass of a cosmic object, the more extreme the deformation of space it causes.
Light travels through the universe in straight lines, but when it encounters a deformation caused by a truly massive object, its path is curved. When the warped object is between Land and a background object, you can bend the light in such a way that the apparent position of the background object is shifted.
But when the intermediate or “lens object” is truly massive, like a monstrous group of galaxiesfor example, light from the background source takes a different amount of time to reach Earth depending on how close it passes through the natural cosmic lens.
This effect, called gravitational lensing, you can make individual objects appear at multiple points in the sky, often in surprising arrangements called Einstein rings and Einstein crosses. It can also make background objects appear magnified in the sky, a powerful effect astronomers use to observe faint, distant, early galaxies.
Distortion caused by massive clusters like eMACS J1823.1+7822 may also help astronomers study mysterious dark matter, which represents about 85% of the mass of the universe but is invisible because it does not interact with electromagnetic radiation. However, because dark matter interacts gravitationally, the lensing of light from a galaxy or a galaxy cluster can help researchers map the distribution of dark matter.
In the new Hubble image, eMACS J1823.1+7822, made up of a collection of elliptical galaxies, acts as a gravitational lens. The cluster warps the shape of the galaxies around it, giving them a slightly elongated shape, turning some into arcs and others into bright streaks.
This particular image was created using Hubble’s Advanced Camera for Surveys and its Wide Field Camera 3 instrument, both of which have the ability to see galaxies and stars in specific wavelengths of light. Observing objects at different wavelengths in this way allows for a more complete picture of the structure, the researchers say.
In turn, such observations can reveal the composition and behavior of an object that would be hidden only in visible light. When combined with the use of clusters such as eMACS J1823.1+7822, gravitational lensing makes it possible to do this for some of the oldest galaxies in the universe. Observatories as powerful as Hubble and the James Webb Space Telescope can probe for conditions encountered shortly after the big Bang and the very birth of the universe.
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