Posted on 05/22/2024 12:04:05 PM PDT by Red Badger
Two dwarf galaxies (top and bottom) orbit the much larger Andromeda galaxy. DAVID DAYAG/WIKIMEDIA COMMONS
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When astronomers fret about the “missing satellites problem,” they’re not talking about spacecraft in Earth orbit. Their problem is much bigger: For decades, far fewer dwarf galaxies have been seen orbiting the Milky Way and other large galaxies than predicted by models of galaxy formation. But now, two groups of astronomers have found evidence for not just a sufficient number of satellite galaxies to satisfy the simulations—but too many.
“Maybe we’ve oversolved the problem,” says Marcel Pawlowski, an astronomer at the Leibniz Institute for Astrophysics Potsdam and a co-author of one of the studies. The results suggest models of galaxy formation need adjusting, perhaps by tweaking the mysterious dark matter that drives them or by adding other factors, such as primordial magnetic fields.
In the standard models of galaxy formation, dark matter—the as-yet-undetected substance that makes up 85% of the matter in the universe—provides the gravitational pull. Soon after the big bang, giant spherical “halos” of dark matter would have attracted clouds of hydrogen and helium, causing them to condense into hundreds of billions of stars that would gather in galaxies. Simulations show each giant dark matter halo would also contain hundreds or thousands of subhalos that would spawn much smaller dwarf galaxies. These satellites would contain just 100 million to 1 billion or so stars and orbit the main galaxy.
But through the 1990s and 2000s, astronomers had only detected about 10 dwarf galaxies around the Milky Way—a small fraction of the predicted number. Over time, the problem eased as bigger telescopes detected dozens of new faint dwarf galaxies. Moreover, researchers have found that galaxy formation may not be as efficient as they once thought, says Sownak Bose, an astronomer at Durham University. Updated models suggest the Milky Way should have about 220 satellites—not too far off from the 60 or so that have been detected by now.
But in April, Masashi Chiba, an astronomer at Tohoku University, and colleagues reported the results of a 7-year survey using the Subaru Telescope in Hawaii. In a relatively small portion of the sky, they found five new Milky Way satellites, the team reported in a preprint on arXiv. Extrapolating their results to the whole sky suggests the Milky Way should have about 500 satellites. “We found too many,” Chiba says.
Pawlowski and his colleagues reported evidence for a similar overabundance around other galaxies, in a study published last month in Astronomy & Astrophysics. They analyzed data from a survey undertaken by the Canada–France–Hawaii Telescope in Hawaii that included nearly 50 galaxies up to 150 million light-years from Earth. Their simulations suggested the survey should have picked up an average of three satellites per galaxy, but instead it found about 10 for each one. “Initially this was posed as a missing satellites problem,” Pawlowski says. “Now it looks like it’s going the other way.”
Modest tweaks to the galaxy formation models could be enough to explain the observations, Pawlowski says. “We must not overinterpret our simulations,” he says. “It doesn’t necessarily mean that the underlying framework of the cosmological model is wrong.”
Dwarf galaxy formation might happen at much smaller scales than anticipated, for example. “What is the smallest dark matter halo that could host a galaxy?” Bose says. “That is an open and very hotly debated question.” Even without changing any dark matter parameters, Stacy Kim, an astrophysicist at the Carnegie Institution for Science, has found that when she runs simulations at extra high resolution, dwarf galaxies form inside dark matter halos of “crazy” low mass, perhaps just 1 million times that of the Sun. “If that’s the case, that would dramatically increase the number of galaxies we expect to see around the Milky Way,” she says.
Magnetic fields that may have arisen just after the big bang could also explain a large number of small galaxies, says Mahsa Sanati, an astrophysicist at the University of Oxford. She says forces from these primordial fields could cause dark matter to clump more readily, leading to more subhalos and more dwarf galaxies. In this scenario, dwarf galaxies might be surrounded by their own, even smaller satellites, she says.
The upcoming Vera C. Rubin Observatory, under construction in Chile, could offer some answers. As it surveys the sky out to unprecedented distances, it is expected to find 40 million cosmic objects, dwarf galaxies among them. “Rubin is going to be able to detect dwarf galaxies that are way fainter than we’ve ever seen before,” Kim says. Once it begins its survey next year it’ll be “a whole new world of dwarf galaxies,” she says.
First there were not enough, now there are too many?.................
Advancing research into the cosmos is generating an increasing number of “problems” for standard theory. Gravity seems to work differently with mega galaxy clusters, dark matter still a mystery, now this; As Thomas Kuhn demonstrated years ago, when anomalies mount up, the time becomes ripe for a scientific revolution.
Gee, I thought the science was settled. /sarc
Once you create a theory, and talk about it often enough, it becomes real and everything else will stem from that theory.
Dark matter is still theoretical, but, explanations for everything that occurs or is observed in the universe. has become dependent on something that is still not proven to exist. It’s like all strange things that have no explanation in the world can be explained by the existence of ‘ghosts’.
not just a sufficient number of satellite galaxies to satisfy the simulations—but too many.
They are going to call the area Munchkinland
Here we go again. Pseudoscience.
Not just ghosts. God. Blah blah blah .... and then a miracle happens!
Many of their theories (multiverse, simulation, string, etc) are indistinguishable from theology.
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