The Milky Way is not alone in its little corner of the universe.
Small, faint dwarf galaxies, some with fewer than a thousand stars, orbit our cosmic neighborhood in long, graceful orbits. It’s unclear exactly how many of these galaxies there are, but it’s likely to be many more. 60 or so We have found so far.
Astronomers have recently identified two more of these small planets, but that news doesn’t quite solve the problem as you might think. Now it looks like there are more of them than necessary.
This is because the two new moons, dubbed Virgo 3 and Sextance 2, were discovered in a region of space that is already crowded with more dwarf galaxies than dark matter models predict.
“Including four previously known satellites, there are a total of nine satellites in the HSC-SSP band.” Write a team led by Daisuke Homma National Astronomical Observatory of Japan.
“The detection rate of very faint dwarfs is much higher than that predicted by recent models of the Milky Way’s satellite population under cold dark matter models, suggesting that we have a ‘too many satellites’ problem.”
Dark matter is an invisible and unknown substance in the universe that contributes to an increase in gravity that cannot be attributed to ordinary matter. Galaxies, including the Milky Way, are saturated and surrounded by this mysterious substance, giving more speed to galactic rotation and more gravitational force to attract, hold and eventually devour satellite galaxies.
Based on models of dark matter in the Milky Way, astronomers predict that the galaxy should have many more dwarf galaxies than have been detected so far. That doesn’t necessarily mean that these galaxies don’t exist, and scientists are working hard to find them in the dark.
Dark matter models also give us fairly detailed predictions about how many satellite galaxies we should expect to see in particular locations, and this is where Virgo III and Sextans II pose a problem.
Homma and colleagues studied data from the Subaru Strategic Program (SSP) Hyper Suprime-Cam (HSC) to survey a portion of space, looking for satellite galaxies of the Milky Way. According to dark matter models, there should be about four dwarf satellite galaxies in that part of the sky.
With the discovery of the two new galaxies, the total number of satellites in that region has risen to nine. Even before the discovery of the two galaxies, the number of satellites there was so high that it was difficult to explain.
Moving things around—except for the classic dwarf galaxy Sextans, for example, or using a different model to predict how many moons we should see—doesn’t solve the problem either.
The best model currently predicts that there are about 220 dwarf galaxies orbiting the Milky Way. If we apply the distribution we found in the HSC-SSP fingerprint to the rest of the space around our galaxy, that total number would actually be closer to 500 satellites.
But it’s possible that the HSC-SSP footprint contains a higher concentration of satellites than the average part of space. The only way to determine whether this is the case is to continue looking at other patches of sky, and counting the dwarf galaxies we find there.
“The next step is to use a more powerful telescope that captures a wider view of the sky.” Astronomer Masashi Chiba says From Tohoku University. “Next year, Vera C. Rubin Observatory “The new satellite galaxies in Chile will be used for this purpose. I hope that many new satellite galaxies will be discovered.”
The research was published in Publications of the Japanese Astronomical Society.
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