A galaxy floating alongside our own, some 380,000 light-years from Earth, may provide new clues in the 90-year quest to determine the nature of dark matter, the invisible glue that holds galaxies together.
The mysterious substance makes up over 80% of the mass of the universe, but has yet to be directly detected.
Scientists say that the satellite galaxycalled Crater II, may consist of self-interacting dark matter (SIDM), which is a hypothetical variety of dark matter whose particles are predicted to interact via a hitherto unknown force gravity. This hypothesis has gained attention in recent years as an alternative form of conventional “cold” dark matter.
“When we started this project, we knew roughly how SIDM would work, but we had no idea how well it would work in explaining the Crater II observations,” study co-author Hai-Bo Yu, who is a professor of physics and astronomy. at the University of California, Riverside, told Space.com.
“Our computer simulations of Crater II analogs show that the agreement between [self-interacting dark matter] The predictions and observations of Crater II are surprisingly good, and the required strength of the dark matter self-interaction is greater than we had originally predicted.”
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Discovered in 2016 in images taken from Very large telescope in Chile, the Crater II galaxy is the fourth largest satellite Milky Way – behind the Large and Small Magellanic Clouds and the Sagittarius Galaxy. If it were visible to the naked eye, it would appear twice as large as the full moon, according to Young scientist. Crater II hosts several billion old stars, which are scattered across 6,500 light-years, making the “faint giant” extremely faint – almost 100,000 times fainter than the Milky Way.
Despite numerous attempts over the years to simulate the properties of Crater II, how the galaxy formed and maintains its relatively large size remains unclear. Astronomers know that Crater II evolves over eons under the gravitational influence of the Milky Way; our galaxy exerts a tidal force on it, which stretches its profile. These pulls also affect its dark matter halo—a spherical, invisible structure surrounding Crater II—as well as the galaxy’s stars.
“A useful analogy is that the tidal force of MONDAY leads to ocean tides in earth“For Milky Way satellites, the tidal force can remove stars and dark matter, reducing the satellites’ mass over time.”
However, recent measurements of the galaxy’s orbit around the Milky Way suggest that those interactions are too weak to explain Crater II’s dark matter density—that is, if the dark matter consists of “cold,” collisionless particles, as predicted by the prevailing Lambda. The CDM (LCDM or CDM) model of cosmology. Prolonged tidal interactions with the Milky Way must also have shrunk Crater II more than observed, the scientists say.
Based on measurements of Crater II’s orbit, Yu and other team members simulated the mass loss of stars and dark matter particles due to the tidal force of the Milky Way. The team found that the observed properties of the galaxy can be explained by dark matter particles interacting with each other.
Most importantly, Crater II does not have a “peak” of high-density dark matter toward its center, as predicted by the LCDM model. On the other hand, if dark matter is indeed made of self-interacting particles, collisions in the inner regions of a dark matter halo can transfer energy between the particles “and tend to make them keep the same amount of energy,” said Yu. This would balance out Crater II’s halo and explain its lack of a central rim, according to the team. STUDYwhich was published this month in The Astrophysical Journal Letters.
SIDM also predicts that a galaxy will expand within the dark matter halo, which would explain Crater II’s large size better than CDM models, the researchers say.
“Our work shows that SIDM can well explain the unusual properties of Crater II, which challenges CDM,” said Yu. “To further confirm whether dark matter does indeed carry a new force, we hope to see more galaxies like Crater II.”
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