A fresh analysis of a remarkably massive yet compact galaxy from the early universe suggests that dark matter interacts with itself.
The galaxy, JWST-ER1, which formed just 3.4 billion years after the Big Bang, was first spotted last October in images snapped by NASA’s James Webb Space Telescope (JWST). At over 17 billion light-years from Earth, JWST-ER1g is the farthest-ever example of a perfect “Einstein ring” — an unbroken circle of light around the galaxy, a result of light rays from a distant, unseen galaxy being bent due to the space-warping mass of JWST-ER1.
The cosmic mirage is not just a pretty sight from a lucky alignment of galaxies; it also offers physicists a valuable probe for model-independent measurements of the mass enclosed within the ring’s radius.
By calculating just how much JWST-ER1g has warped space-time around itself, the discovery team had estimated that the galaxy weighs about 650 billion suns, which makes it a peculiarly dense galaxy for its size. By subtracting the visible stellar mass from the total inferred mass, physicists can measure how much of the galaxy is dark matter, an invisible substance thought to make up over 80% of all matter in our universe.
Despite decades of observations and heaps of circumstantial evidence, the elusive substance is yet to be directly detected. In JWST-ER1g, the discovery team determined that dark matter explains just about half the mass gap, and that “additional mass appears to be needed to explain the lensing results,” according to the discovery paper, which was published last fall.
“The value for the dark matter mass seems higher than expected,” Hai-Bo Yu, a professor of physics and astronomy at the University of California, Riverside (UCR) and a co-author of the new study, said in a statement. “This is puzzling.”
In a new paper, Yu and his colleagues suggest that JWST-ER1g’s unusually high density could be explained by a higher population of stars than currently thought. However, a contraction mechanism by which ordinary matter — the stuff that makes up gas and stars — “collapses and condenses” into JWST-ER1g’s dark matter halo could be packing “more dark matter mass in the same volume, resulting in higher density,” study lead author Demao Kong of UCR said in the same…
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