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Dark matter puzzle depends in part on whether our galaxy is an “outlier”

Milky Way, artist’s impression/NASA/JPL-Caltech/ESO/R

Twenty years ago, astronomers couldn’t find enough satellite galaxies orbiting the Milky Way. Now there seem to be too many. Some information seems to be missing. A possible solution is that many of these galaxies are dwarfs formed by dark matter:

Most cosmologists believe that dark-matter particles are “cold,” meaning that they move slowly. Because of this, they can coalesce into numerous tiny halos, providing scores of places where dwarf galaxies can form. But “warm” or “hot” dark matter, which by definition moves faster, cannot coalesce so easily. In fact, hot particles wouldn’t be able to form mini-halos at all. So the sheer existence of these small galaxies is a sign that warm dark matter is likely not at play. “It’s very bad news for alternative dark-matter scenarios,” Bullock said. “They’re just dead on arrival.”

And the importance of that cannot be underestimated. “This is the big Holy Grail — to try to pin down what the particle properties of dark matter are so that we can understand this missing component of the universe,” said Alex Drlica-Wagner, an astronomer at the Fermi National Accelerator Laboratory.

And it comes at a crucial time. Willman admits that she had started to wonder whether scientists would ever be able to truly use these tiny galaxies to learn something fundamental about dark matter. Shannon Hall, “Missing Galaxies? Now There’s Too Many
” at Quanta

The trouble is, as the article goes on to point out, our galaxy may be an outlier. Like ourselves, maybe.

See also: Does An Arrested Galaxy Violate The Second Law Of Thermodynamics?

Our Milky Way Galaxy Is Twice As LargeAs Previously Thought?

Experimental physicist Rob Sheldon takes issue with News’s globular clusters story Sheldon: A physics model is always incomplete. Some missing piece of trivia will turn out to be important. So always take models, even elaborate expensive super-computer models, with many grains of salt. They are only as good as the assumptions that go into them.


Are globular clusters 4 billion years younger than previously thought? It “brings into question” more than the mechanics of galaxy formation. There is considerable distance between nine billion years and thirteen billion years. An equivalent claim for life on Earth would shave a billion years off the development of life. If it’s true, it’s true. But the finding doesn’t fill onlookers with confidence about the accuracy of dating systems.

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