The phenomenon of “identical objects” explained with a discovery that could have implications for the understanding of dark matter.
Galaxies may have many characteristics in common, but no two are exactly alike. For this reason, in 2013, when two galaxies, at the far ends of the Universe, seemed to be surprisingly similar, side by side, the astronomers were perplexed. Now they have finally solved the mystery of this “identical object” in space, called Hamilton’s Object named after the astronomer of Shawnee State University in Portsmouth, Ohio, Timothy Hamilton who almost a decade ago accidentally discovered this pair of galaxies from data obtained from the Hubble Space Telescope. “We didn’t know what to think – Hamilton said -. The first thought was that maybe we were interacting with other galaxies, but the patterns didn’t fit very well.”.
Only in 2015 would a plausible reason emerge. Astronomer Richard Griffiths of the University of Hawaii, seeing Hamilton present his object at a meeting, suggested that the culprit could be a rare phenomenon, called gravitational lens, purely due to a random alignment of massive objects in space. When a massive object aligns between us and a more distant object, a magnification effect occurs due to the gravitational curvature of space-time around the nearby object. Any light traveling in this space-time follows this curvature and is detected as being distorted to varying degrees, but also often enlarged and duplicated.
In support of the phenomenon, Griffiths and his team began searching for detection data for an object massive enough to produce the lens effect, finding a poorly documented cluster of galaxies hiding between us and Hamilton’s object. The work of the team, published in the Monthly Notice of the Royal Astronomical Society, revealed that Hamilton’s object is located about 11 billion light years away, and work by another team indicated that the cluster is about 7 billion light years away.
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Snapshot of the Hubble Space Telescope shows magnified images of a distant galaxy embedded in a cluster of galaxies. The “identical objects” are due to a phenomenon called gravitational lensing / NASA
The galaxy itself is a barred spiral galaxy, in the process of lumpy and irregular star formation. Computer simulations then helped determine that duplicate images can only be created if the distribution of dark matter is uniform on small scales. “This already gives us an idea of how smooth the dark matter of these two locations must be”Pointed out the astronomer Jenny Wagner of the University of Heidelberg in Germany.
The researchers determined that the two identical images are created because “straddle a ripple in space-time, an area of greater magnification created by the gravity of a dark matter filament“. Such filaments are thought to link the Universe in a vast invisible cosmic web, joining galaxies and galaxy clusters, but in reality we don’t know what dark matter is, so each new discovery that allows us to map where it is, how it is distributed and how it affects the surrounding space is another piece of evidence that will ultimately help solve this mystery as well.
“We know it’s some form of matter, but we have no idea what the constituent particle isGriffiths explained -. So we don’t know how it behaves at all. We only know that it has mass and is subject to gravity. The significance of the size limits on aggregation or smoothness gives us clues as to what the particle might be. The smaller the clusters of dark matter, the more massive the particles must be”.