This Hubble Space Telescope snapshot features three magnified images showing a distant galaxies embedded in a cluster. Gravitational lensing is a trick of nature that produces these images. Multiple images are created by the galaxy cluster's enormous gravity. It magnifies and distorts light from distant galaxies behind it. The two magnified images at the bottom right are identical copies of each other. These two bright ovals represent the cores of this galaxy. This rare phenomenon is caused by the background galaxy crossing a ripple in space's fabric. This is the area with greatest magnification due to dense dark matter.
Astronomers believe that they have finally solved a mystery discovered by the Hubble Space Telescope almost ten years ago.
The mystery was centered around a "double galaxy", a pair of streaky, mysterious objects that had previously defied explanation. Scientists now believe that the objects are actually one distant galaxie that appears to be two due to a ripple in space's fabric that magnifies and distorts its image.
The doubled objects, which are almost 11 billion light years away from Earth, look like mirror images. Astronomers first noticed them in 2013. They immediately recognized a case for gravitational lensing, a phenomenon where light from faraway objects is warped by gravity.
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This answered the how but not the why. Hubble has seen many gravitationally lensed objects over its lifetime, but this one was far more than a warp. Gravitational lensing allowed for the magnifying of the galaxy and copying it. This created two bright images as well as a fainter copy that can be seen in this image.
Astronomers finally found the answer after years of searching for the cause. A large cluster of galaxies lies between Hubble's object and Hubble, approximately 7 billion light-years away from Earth. The lensed galaxy also happens to be on a ripple in space caused by gravity of densely-packed dark matter, which is the mysterious stuff that accounts for about 85% of all the matter in our universe.
Researchers said that the extra images were created when light from the distant star passed through the cluster in the foreground, along with a ripple.
Richard Griffiths, an Astronomer at the University of Hawaii, Hilo said, "Think of the rippled pool surface on a sunny afternoon, showing patterns of bright sunlight on the bottom of it."
Griffiths, who was the lead author of the study that announced the findings, said "These bright patterns at the bottom are caused by a similar effect to gravitational lensing." "The surface ripples act as partial lenses, focusing sunlight onto bright patterns at the bottom."
Team members stated that the "ripple" could aid astronomers in better understanding how dark matter is distributed across the universe. The researchers found that dark matter was not clumpy when they compared Hubble images with computer models.
Jenny Wagner, an astronomer from Heidelberg University, Germany, stated in the same statement, "It's amazing that we only require two mirror images to get the scale on how clumpy and not dark matter can exist at these positions."
The September issue of Monthly Notices of Royal Astronomical Society featured the study.