Hi everyone,
Here is a news item about a galaxy that does not seem to have any Dark Matter at all.
https://news.nationalgeographic.com/2018/03/dark-matter-galaxy-gravity-dragonfly-physics-space-science/**********
An unusual galaxy far, far away is stumping astronomers not because of what’s there, but because of what’s missing.
Normally, not all of a galaxy’s mass is visible. In addition to a mix of ordinary matter—like stars and planets and manatees—galaxies are expected to contain dark matter, an invisible substance that makes up most of the mass in the universe. Although we can’t directly observe it, we know dark matter is there because we can see how its gravity affects ordinary matter.
Based on the ratio in other galaxies, an isolated galaxy like NGC1052-DF2 should have about a hundred times more dark matter than ordinary matter. But this one appears to have … almost none, scientists report today in Nature.
By tracking the motion of 10 embedded star clusters, the team could determine how much mass is tucked into the galaxy. And surprisingly, it’s about the same amount of mass they’d expect to see from the galaxy’s stars alone.
One strange observation doesn’t necessarily break a theory. But finding a galaxy that’s more or less devoid of dark matter certainly suggests a few tantalizing things. First, it really challenges ideas about how galaxies form.
“There’s a pretty tight relationship between the amount of stars that formed and the dark matter there, at least when the galaxy formed.”
In other words, no dark matter, no galaxy.
....if it turns out that galaxies can form in the absence of dark matter, it would be stunning.
“I would need to rethink what a galaxy is,” she says.
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Cheers.
Sriram
