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Dark matter, the mysterious invisible matter that makes up most of the mass of galaxies, including our own Milky Way, is once again confusing scientists, with new observations of distant galaxies that conflict with current understanding of their nature.
Research published this week revealed an unexpected discrepancy between observations of dark matter concentrations in three massive galaxy clusters spanning trillions of stars and theoretical computer simulations of how dark matter should be distributed.
“Either an ingredient is missing in the simulations or we’ve made a fundamental wrong assumption about the nature of dark matter,” Yale University astrophysicist Priyamvada Natarajan, co-author of the study published in the journal Science, said on Friday.
Dark matter is the invisible glue that holds the stars together within a galaxy. It also creates an invisible scaffold that allows galaxies to form clusters. But it has very peculiar properties. It does not emit, absorb or reflect light and does not interact with any known particles.
Most of the matter in the universe, about 96 percent, is believed to be dark matter, with ordinary matter, the visible matter that makes up stars, planets, and people, just 4 percent.
The presence of dark matter is known only through its gravitational pull on visible matter in space. It differs from the equally enigmatic and invisible dark energy, which is considered a property of space and is driving the accelerating expansion of the universe. Dark energy is repulsive. Dark matter is attracted by gravity.
The new study involved observations from the Hubble Space Telescope and the Very Large Telescope of the European Southern Observatory in Chile.
When light from distant sources like distant galaxies travels through matter like another galaxy or a cluster of them, the light is deflected and bent, a phenomenon called “gravitational lensing,” said astrophysicist and lead author of the study Massimo Meneghetti of the Astrophysics Observatory. and Space Sciences in Bologna and the National Institute of Astrophysics in Italy.
The new observations showed that the gravitational lensing effects produced by galaxies residing within huge galaxy clusters were much stronger than current dark matter theory imagined, suggesting an unexpectedly large concentration of dark matter in these galaxies.
“This is quite surprising,” Meneghetti said.
© Thomson Reuters 2020
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