Cosmic “telescopes” –dark matter lenses– which warp light like funhouse mirrors in the form of the gravitational fields of dark matter clumps, may create “efficient lenses” that can magnify light from distant reaches of the universe revealing previously unknown objects and phenomena. Although dark matter is invisible because it does not emit light, that does not mean that it doesn’t interact with light at all and can be observed by space telescope such as the NASA/ESA Hubble observatory.
These lenses, says Massimo Meneghetti, a cosmologist at the Astrophysics and Space Science Observatory of Bologna, could help astronomers observe remote objects located behind the lenses from our perspective on Earth and test out fundamental theories about the universe. Scientists led by Meneghetti have set out to estimate how many of these small dark matter lenses might be embedded in galaxy clusters, that can contain thousands of gravitationally-bound galaxies and test predictions of the cold-dark-matter model.
Dark matter is one of the dominant constituents of the universe, which piled up in certain parts of the universe due to gravity, and in those regions, galaxies were formed. It is the unseen thing that holds the universe together, said Yale theoretical astrophysicist Priya Natarajan.
Cold Dark Matter -Tests with Flying Colors
Although the type of particle that makes up dark matter is still a mystery, in January of 2020 a NASA team using the Hubble Space Telescope made a very compelling observational test for the cold dark matter model that passes “with flying colors,” said Tommaso Treu of the University of California, Los Angeles (UCLA), a member of NASA’s team who used a new “cosmic magnifying glasses” technique that found that dark matter forms much smaller clumps than previously known, confirming one of the fundamental predictions of the widely accepted “cold dark matter” theory consisting of slow-moving, or “cold,” particles that come together to form structures ranging from hundreds of thousands of times the mass of the Milky Way galaxy to clumps no more massive than the heft of a commercial airplane.
“Although tend to think about dark-matter particles as being tiny, theoretically, there is no reason they can’t be as big as a galaxy,” says theoretical physicist Asimina Arvanitaki, at the Perimeter Institute for Theoretical Physics referring to the heated debate about the standard model for dark matter that proposes that it is ‘cold,’ meaning that the particles move slowly compared to the speed of light which is tied to the mass of dark matter particles. The lower the mass of the particle, the ‘warmer’ it is and the faster it will move.
If small dark matter lenses turn out to be abundant in galaxy clusters, it could help astronomers peer into otherwise unobservable corners of the universe. The lensing phenomena occurs when a gravitationally influential object, perhaps a dark matter clump, aligns with a source of background light, such as a distant galaxy. As the light travels through the gravitational field of the object, it can become substantially brighter, as if amplified by a cosmic telescope.
“Dark matter is colder than we knew at smaller scales,” said Anna Nierenberg of NASA’s Jet Propulsion Laboratory, leader of the Hubble survey who pioneered using strong gravitational lenses to act as tracers, providing powerful insight into the fundamental properties of dark matter. “Astronomers have carried out other observational tests of dark matter theories before, but ours provides the strongest evidence yet for the presence of small clumps of cold dark matter. By combining the latest theoretical predictions, statistical tools and new Hubble observations, we now have a much more robust result than was previously possible.”
“Often the source is magnified, meaning that we have the chance to see tiny details in the lensed images that we would not be able to detect without gravitational lensing,” said Meneghetti.
“If we can build a reliable model of how the matter is distributed in the lens, then we can use the model to correct the shape of the lenses’ sources,” Meneghetti explained about the lenses tendency to mangle the image of the background sources, which means that scientists have to figure out a way to reverse-engineer the original shapes of objects from the deformed lensed versions.. “This is very interesting! Using this effect, we can see what very distant and young galaxies look like.”
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