Missing Dwarf Galaxies Found Near The Milky Way in The Worst Place

The Milky Way is surrounded by a multitude of small, faint dwarf galaxies, some with as few as a thousand stars. Although the exact number of these galaxies is unknown, it is believed that there are significantly more than the 60 that have been discovered so far. Recently, two more of these dwarf galaxies, named Virgo III and Sextans II, were identified. However, this discovery has led to a conundrum known as the ‘too many satellites’ problem.

The issue arises because the region of space where these two new galaxies were found already contains more dwarf galaxies than models of dark matter predict. With the addition of Virgo III and Sextans II, there are now nine dwarf galaxies in this region, which is higher than the predicted number based on dark matter models.

Dark matter is an invisible, unknown substance that contributes additional gravity to galaxies, including the Milky Way. Based on models of the Milky Way’s dark matter, astronomers expect that the galaxy should have many more dwarf galaxy satellites than have been found to date. The locations of these satellites are also predicted by these models, and the discovery of Virgo III and Sextans II in a region with a higher-than-predicted number of satellites is causing confusion.

The best current model predicts that there should be around 220 dwarf galaxies orbiting the Milky Way. If the distribution found in the HSC-SSP footprint is extrapolated to the rest of the space around our galaxy, the total would be closer to 500 satellites. It is possible that the HSC-SSP footprint contains a higher concentration of satellites than the average section of space. To determine whether this is the case, astronomers plan to continue looking at other patches of the sky and counting the dwarf galaxies they find there.

The research team, led by Daisuke Homma of the National Astronomical Observatory of Japan, published their findings in the Publications of the Astronomical Society of Japan. They hope that future observations with more powerful telescopes, such as the Vera C. Rubin Observatory in Chile, will help resolve the ‘too many satellites’ problem and provide a better understanding of the distribution and nature of dwarf galaxies in the Milky Way’s neighborhood.

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