Astronomers have discovered two new satellite galaxies of the Milky Way, and the findings could help us better understand dark matter – the mysterious substance that makes up about 85% of the matter in the universe, yet remains virtually invisible to us.
The discoveries also bring scientists one step closer to solving a lingering problem with the Standard Model of cosmology, or the “lambda cold matter model,” also known as the “ΛCDM’, in which the word ‘cold’ assumes that dark matter consists of particles moving slower than the speed of light.
The newly found small gatherings of stars were designated Sextans II and Virgo III. They join about 60 known dwarf galaxies that swarm around our much larger home spiral galaxy at maximum distances of 1.4 million light-years. The best known and largest of these satellites of the Milky Way’s dwarf galaxies are the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC).
“How many satellite galaxies does the Milky Way have? This has been an important question for astronomers for decades,” team leader Masahi Chiba, a professor at Tohoku University, said in a statement.
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Many small satellites of the Milky Way’s dwarf galaxies remain undiscovered due to their distant and faint nature, but Chiba and colleagues were determined to begin finding these elusive objects. So they turned to the Subaru telescope. Located near the summit of Maunakea in Hawaii, this powerful ground-based telescope is well-suited to hunting dwarf galaxies, and the same team previously used it to detect three new satellites of the Milky Way.
Help! Our dwarf galaxy is missing
Dark matter is a persistent cosmological problem because it does not interact with light or with the ordinary matter that makes up stars, planets, moons, and us. And if it interacts with those things, those interactions are too weak for us to notice.
This means that dark matter could be composed of particles that are currently undiscovered, although there are potential explanations that do not require an extension of particle physics. For example, scientists have explored the idea that dark matter could be made from tiny primordial black holes left over just after the big bang.
However, dark matter does interact with gravity, which can affect the motion and dynamics of light and everyday matter. This allowed scientists to infer the presence of dark matter and ultimately determine that large galaxies are surrounded by huge halos of this mysterious substance. These halos are believed to extend far beyond the galactic disks and the halo of visible matter.
The ΛThe CDM predicts that this dark matter halo played a significant role in the evolution of galaxies. In the early universe, they created gravity wells into which the gas and dust that formed stars in galaxies were drawn. Eventually, this halo also coalesced to form large galaxies such as the Milky Way.
This model also suggests that there should indeed be hundreds of satellite galaxies around the Milky Way and other large galaxies. For example, using simulations ΛCDM predicts that our neighboring galaxy, Andromeda, should be surrounded by about 500 satellite galaxies. However, astronomers have seen only 39 dwarf galaxies swirling around Andromeda.
For the Milky Way, some simulations based on the Standard Model of Cosmology suggest that there should be about 220 dwarf galaxies orbiting our galaxy, but scientists can’t figure out where they all are. The discovery of Sextans II and Virgo III helps to redress this balance. Still, the results from these findings could present cosmologists with the opposite problem they’ve faced before.
Not enough dwarf galaxies or too many?
Although the number of Milky Way galaxies identified is still significantly lower than the predicted 220 dwarf galaxies, the team behind this research took into account the fact that Subaru cannot see the entire night sky above Earth.
They combined the distribution of dwarf galaxies that Subaru could see with its “footprint” of the night sky to calculate an estimate of the number of satellites. should, they actually surround our galaxy. This led to the calculation that 500 galaxies surround the Milky Way—more than twice the amount predicted by simulations based on ΛCDM.
So have scientists gone from a “problem of not enough dwarf galaxies” to a problem of “too many dwarf galaxies”?
Maybe not. Recently, amateur astronomer Giuseppe Donatiello discovered five new satellite galaxies around the Sculptor Galaxy, officially known as NGC 253.
When he and a team of astronomers looked at the distribution of satellite galaxies around the Sculptor Galaxy, including three previously found by Donatiello himself, they found that the distribution of these galaxies, located about 11.5 million light-years from Earth, is uneven. . In other words, the small galaxies appeared to have a “preferred direction”, with more galaxies lying on one side of the Sculptor galaxy than the other.
If there is also a favored direction for dwarf galaxies around the Milky Way, and the Subaru telescope happens to be looking in that direction, then the estimates based on the Subaru observations would be inflated.
The team behind these discoveries of Milky Way dwarf galaxies now intends to further investigate the true number of satellite galaxies surrounding us using another ground-based telescope.
“The next step is to use a more powerful telescope to capture a wider view of the sky,” Chiba concluded. “Next year, the Vera C. Rubin Observatory in Chile will be used to fulfill this purpose. I hope that many new satellite galaxies will be discovered.”
The team’s results were published June 8 in Publications of the Astronomical Society of Japan.